Bluefin trevally
Encyclopedia
The bluefin trevally, Caranx melampygus (also known as the bluefin jack, bluefin kingfish, bluefinned crevalle, blue ulua, omilu and spotted trevally), is a species
of large, widely distributed marine
fish
classified in the jack family, Carangidae
. The bluefin trevally is distributed throughout the tropical waters of the Indian
and Pacific Ocean
s, ranging from Eastern Africa in the west to Central America
in the east, including Japan
in the north and Australia
in the south. The species grows to a maximum known length of 117 cm and a weight of 43.5 kg
, however is rare above 80 cm. Bluefin trevally are easily recognised by their electric blue
fins, tapered snout and numerous blue and black spots on their sides. Juveniles lack these obvious colours, and must be identified by more detailed anatomical features such as fin
ray and scute
counts. The bluefin trevally inhabits both inshore environments such as bays, lagoon
s and shallow reef
s, as well as deeper offshore reefs, atoll
s and bomboras. Juveniles prefer shallower, protected waters, even entering estuaries for short periods in some locations.
The bluefin trevally is a strong predatory fish, with a diet dominated by fish and supplemented by cephalopod
s and crustacean
s as an adult. Juveniles consume a higher amount of small crustaceans, but transfer to a more fish based diet as they grow. The species displays a wide array of hunting techniques ranging from aggressive midwater attacks, reef ambush
es and foraging
interactions with other larger species, snapping up any prey items missed by the larger animal. The bluefin trevally reproduces at different periods throughout its range, and reaches sexual maturity
at 30–40 cm in length and around 2 years of age. It is a multiple spawner
, capable of reproducing up to 8 times per year, releasing up to 6 million eggs per year in captivity. Growth is well studied, with the fish reaching 194 mm in its first year, 340 mm in the second and 456 mm in the third year. The bluefin trevally is a popular target for both commercial
and recreational fishermen
. Commercial fisheries record up to 50 tonne
s of the species taken per year in the west Indian Ocean, and around 700 lbs per year in Hawaii
. The rapid decimation of the Hawaiian population due to overfishing
has led to increased research in the aquaculture
potential of the species, with spawning achieved in captivity. Despite its popularity as a table fish, many cases of ciguatera
poisoning have been reported from the species.
, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae
, a group of percoid
fishes in the order Perciformes
.
The species was first scientifically described by the famed French naturalist
Georges Cuvier
in 1833 based on specimens collected off Waigio, Indonesia
; one of which was designated to be the holotype
. He named the species Caranx melampygus, placing the species in the jack genus Caranx which had been established by Bernard Lacépède three decades previously. The name's specific epithet is derived from the Latin translation of "black spotted". This is still currently considered the correct placement, however later authors placed in other now defunct genera (Carangus and Carangichthys) which has since been deemed incorrect, and the original classification stands. The species was independently redescribed and named seven times after Cuvier's initial description, with all of these names assigned between 1836 and 1895. The names C. bixanthopterus and C. stellatus were often used in the literature, and were variably classed as synonyms
of C. melampygus or valid individual species after their naming. This confusion culminated in Yojiro Wakiya concluding in 1924 they should be treated as separate species. The taxonomy of the species was finally revised by Frederick Berry in 1965, who resolved these two names as being synonymous with C. melampygus, and placed several other names in synonymy with C. melampygus. Under ICZN
nomenclature rules, these later names are deemed junior synonyms of C. melampygus and rendered invalid. The species hat not been included in any detailed phylogenetic studies of the Carangidae.
The species is most commonly
referred to as the 'bluefin trevally', with the species's distinctive blue fins contributing to most of its other common names. These include bluefin jack, bluefin kingfish, blue ulua, omilu, bluefinned crevalle and spotted trevally. The species has many other non-English names due to its wide distribution.
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 21 to 24 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 17 to 20 soft rays. The pelvic fins contain 1 spine and 20 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head. The lateral line
has a pronounced and moderately long anterior arch, with the curved section intersecting the straight section below the lobe of the second dorsal fin. The curved section of the lateral line contains 55-70 scales
while the straight section contains 0 to 10 scales followed by 27 to 42 strong scute
s. The chest is completely covered in scales. The upper jaw contains a series of strong outer canine
s with an inner band of smaller teeth, while the lower jaw contains a single row of widely spaced conical teeth. The species has 25 to 29 gill raker
s in total and there are 24 vertebrae present. The eye is covered by a moderately weakly developed adipose eyelid, and the posterior extremity of the jaw
is vertically under or just past the anterior margin of the eye. Despite their wide range, the only geographical variation in the species is the depth of the body in smaller specimens.
The upper body of the bluefin trevally is a silver-brassy colour, fading to silvery white on the underside of the fish, often with blue hues. After they reach lengths greater than 16 cm, blue-black spots appear on the upper flanks of the fish, with these becoming more prolific with age. There is no dark spot on the operculum
. The species takes its name from the colour of its dorsal, anal and caudal fins, which are a diagnostic electric blue
. The pelvic and pectoral fins are white, with the pectoral fin having a yellow tinge. Juvenile fish do not have the bright blue fins, instead have dark fins with the exception of a yellow pectoral fin. Some juvenile fish have also been recorded as having up to five dark vertical bars on their sides.
The bluefin trevally is widely distributed, occupying the tropical and subtropical waters of the Indian
and Pacific Ocean
s, ranging along the coasts of four continent
s and hundreds of smaller islands and archipelago
s. In the Indian Ocean, the species easternmost range is the coast of continental Africa
, being distributed from the southern tip of South Africa
north along the east African coastline to the Red Sea
and Persian Gulf
. The species' range extends eastwards along the Asia
n coastline including Pakistan
, India
and into South East Asia, the Indonesian Archipelago
and northern Australia
. The southernmost record from the west coast of Australia comes from Exmouth Gulf
. Elsewhere in the Indian Ocean, the species has been recorded from hundreds of small island groups including the Maldives
, Seychelles
, Madagascar
and the Cocos (Keeling) Islands
.
The bluefin trevally is abundant in the central Indo-Pacific region, found throughout all the archipelagos and offshore islands including Indonesia, Philippines
and Solomon Islands
. Along continental Asia, the species has been recorded from Malaysia to Vietnam
and mainland China
. Its offshore range does extend north to Hong Kong
, Taiwan
and southern Japan
in the north western Pacific. In the south, the species reaches as far south as Sydney in Australia. Its distribution continues throughout the western Pacific including Tonga
, Western Samoa and Polynesia
, and the Hawaii
an Islands. The easternmost limit of the species distribution is the Mesoamerica
n coastline between Mexico
and Ecuador
in the central eastern Pacific, including islands such as the Galapogos.
and rocky reef
s, lagoon
s, sand flats and seagrass
meadows.
Juveniles and subadults are more common in these settings, and prefer these more protected environments, where they live in water to a minimum of around 2 m depth. Adults tend to prefer more exposed, deeper settings such as outer reef slopes, outlying atoll
s and bomboras, often near drop offs, with the species reported from depths up to 183 m. Adults often enter shallower channel
s, reefs and lagoons to feed at certain periods during the day. The bluefin trevally displays some habitat partitioning with giant trevally
, Caranx ignobilis, tending to be more common outside the major bays than their relatives.
Juvenile and subadult bluefin trevally have been recorded in estuaries in several locations, and generally occupy large, open estuaries up to the middle reaches of the system. These estuaries are often lined by mudflats and mangrove
s, however the species rarely enters these shallow waters. Individuals of between 40 and 170 mm have been recorded in South African estuaries, where they are the least tolerant carangid to the brackish and freshwater conditions of these systems. Bluefin trevally can tolerate salinities
of between 6.0 to 35 ‰, and only occupy clear, low turbidity
waters. There is evidence the species is only resident in these estuaries for short periods. The species is also absent from coastal lakes that many other carangids are known from.
species as a juvenile, transitioning to a more solitary fish with well defined home range
s as an adult. Adults do school to form spawning
aggregations or temporarily while hunting, with evidence from laboratory studies indicates bluefin trevally are able to coordinate these aggregations over coral reef
s based on the release of dimethylsulfoniopropionate
(DMSP) from the reef. DMSP is a naturally occurring chemical produced by marine algae and to a lesser extent coral
s and their symbiotic zooxanthellae. The number of fish present in an area is also influenced by tidal
factors and possibly the abundance of prey and other environmental factors. Tracking studies in Hawaii have found bluefin trevally patrol
back and forth along a home range of patch reef walls during the day, only stopping for variable periods where major depth changes or discontinuities in the reef were present. Several fish patrol the same reef patch, reversing direction where the others do. While most fish patrol the one reef, some have been observed to make excursions to nearby reefs, before returning to their home reef later. Night
time movements are less extensive than daytime movements, with the trevally moving rapidly between several small reef sections, before slowing down and milling in one patch for around an hour. The fish living in a particular region congregate in one area at night, before returning to their individual daytime range during the day. The reason for this congregation is unclear, but may be important to the social structure of the species. Long term studies have found the fish may range up to 10.2 km over several months, however is much less restricted in its movements than its relative, the giant trevally. A Hawaiian biomass
study found the species to be one of the most abundant large predators in the islands, however it is less abundant in the heavily exploited Main Hawaiian Islands compared to the remote Northwest Hawaiian Islands. The main difference in these populations was the relative lack of large adult fish in the inhabited areas compared to the remote, unfished regions. A study on carangids caught during a fishing tournament
in Hawaii found the bluefin trevally is the most common trevally species taken, accounting for over 80% of the carangid catch. The authors note that this may not only reflect its abundance, but also it vulnerability to specific fishing methods used in the tournament. Apart from the typical predator-prey relationship the species shows (described later), an individual of the species has been seen to rub itself against the skin of a Galapagos shark
, apparently to rid itself of parasites. This behaviour is also observed in rainbow runner
and is a rare example of a commensal cleaner relationship where the cleaner does not gain anything.
The bluefin trevally is a fast swimming, mainly piscivorous predator which shows a wide range in hunting techniques. Two studies of adult fish in Hawaii found fish to be the dominant food type in the species, making up over 95% volume of the stomach contents by weight. Here the main fish selected were small reef dwellers, with fish from the families Labridae, Mullidae, Scaridae and Priacanthidae
being the most common. Despite the preference of several families, bluefin trevally do take a very wide variety of fish in small amounts, including various species of eel
. The species appears to have a preference for fish of a specific size, which depends on its own length and age.
Cephalopod
s (mainly octopus
or squid
) and a wide array of crustaceans are also taken in smaller quantities, with shrimp
s, stomatopods and crab
s being the most common. The diet of juveniles in Hawaiian and South African estuaries has also been determined, with these younger fish having a more crustacean based diet than the adults. In Hawaii, crustaceans make up 96% of the gut contents numerically, with tanaids and isopods dominating the diet, while fish (mainly gobioids
) only make up 4% numerically. Juveniles less than 170 mm in South African estuaries feed predominantly on mysids and paenid prawn
s, before shifting to a more fish based diet at larger sizes. Small fish are able to effectively filter these small crustaceans from the water, while adults are not. In both cases, a transition to a more fish based diet with age was found to occur, although the length at which this transition occurred varied between location. The diet overlap with the similar C. ignobilis is low in the Hawaiian Islands, suggesting there is some separation of feeding niches. Calculations suggest each individual bluefin trevally consumes around 45 kg of fish per year on average, making it one of the most effective predators in this habitat.
The bluefin trevally displays a remarkable array of hunting techniques, ranging from midwater attacks to ambush and taking advantage of larger forage fish
. The species is reported to hunt during the day, particularly at dawn
and dusk
in most locations; however it is known to be a nocturnal feeder in South Africa. The bluefin trevally hunts both as a solitary individual and in groups of up to 20, with most fish preferring an individual approach. In groups, these fish will rush their prey, and disperse the school, allowing for isolated individuals to be picked out and eaten, much in the way the related species, giant trevally have been observed to do in captivity. In some cases, only one individual in a group will attack the prey school. Where the prey is schooling reef fishes, once the prey school has been attacked, the trevally chases down the prey as they scatter back to cover in the corals, often colliding with coral as they attempt to snatch a fish. While hunting in midwater, fish swim both against and with the tide
, although significantly more fish hunt when swimming with the tide (i.e. 'downstream'), suggesting some mechanical advantage is gained when hunting in this mode. Another method of attack is ambush
; in this mode the trevally change their colour to a dark pigmentation state and hide behind large coral lumps close to where the aggregations (often spawning reef fish) occur. Once the prey is close enough to the hiding spot, the fish ram the base of the school, before chasing down individual fish. These dark fish in ambush mode vigorously drive away any other bluefin trevally that stray too close to the aggregation. Ambushes have also been observed on small midwater planktivorous fishes are moving to or from the shelter of the reef. In many cases, the species uses changes in the depth of the reef such as ledges to conceal its ambush attacks. Bluefin trevally also enter lagoons as the tide rises to hunt small baitfish in the shallow confines, leaving as the tide falls. The species is also known to follow large rays
, shark
s and other foraging fish such as goatfish
and wrasse
around sandy substrates, waiting to pounce on any disturbed crustaceans or fish which are flushed out by the larger fish.
at between 30 and 40 cm in length and around 2 years in age,
with one study Hawaii suggesting maturation occurs at a length of around 35 cm on average. There is also a difference in the length at maturation between the two sexes, with females on average reaching maturity at 32.5 cm length, while males attain maturity at 35 cm on average. Sex ratio
s in the species vary by location with population off east Africa being skewed towards males (M:F = 1.68:1), while in Hawaii the opposite is true with the M:F ratio being 1:1.48. The period of the year over which spawning
occurs is also variable by location, with African fish reproducing between September and March while in Hawaii this occurs between April and November, with a peak in May to July. Natural spawning behaviour in the species has never been observed, although large aggregations of bluefin trevally observed in Palau
consisting of over 1000 fish are believed to be for the purpose of spawning. Extensive studies on the species in captivity has revealed the species to be a multiple spawner, capable of spawning at least 8 times a year, and up to twice in 5 days. Spawning events are often clustered in a few consecutive or alternate days, usually in the third or fourth lunar phase
s. Spawning apparently occurs at night to minimise predation on egg
s. Fecundity
in the natural environment has been reported to range from around 50 000 to 4 270 000, with larger individuals releasing more eggs. Studies in captive fish show females may produce over 6 000 000 eggs per year. These eggs are pelagic and spherical, with diameter
s between 0.72 and 0.79 mm.
The development of the bluefin trevally larvae
after hatching has been briefly described in a study of changes in the digestive enzyme
s of the species. The species has depleted its storage of energy from the egg at 3 days old, with a series of transformations including coiling of the gut and fin formation occurring before flexion
at 26 days of age. Digestive enzymes active from hatching to 30 days old show an apparent shift from carbohydrate
utilisation to protein
and lipid
utilisation as the larvae grows older. Measurements from juveniles in Hawaii indicate the fish is around 70 mm by 100 days and 130 mm by 200 days. Otolith data fitted to the von Bertalanffy growth curve shows the species grows to 194 mm in its first year, 340 mm in the second and 456 mm in the third year. It reaches 75 cm by 8 years of age and 85 cm by 12 years. This model also suggests a growth of 0.45 mm/day; while laboratory feeding studies found the fish grow at an average of 0.4 mm/day in these confined conditions. The maximum theoretical size indicated from the growth curves is 89.7 cm, much less than the 117 cm reported as the known maximum size. Juveniles often enter estuaries, however the species is not estuary dependant as breeding is known to occur where no estuaries are present, suggesting the use of these habitats is facultative
. The fish move from these shallower inshore waters to deeper reefs as they grow.
Two hybridisation events in the species are known from Hawaii; the first with the giant trevally, Caranx ignobilis and the second with the bigeye trevally
, Caranx sexfasciatus. Both were initially identified as hybrids by intermediate physical characteristics, and were later confiremed by DNA sequencing
. It has been suggested these hybrids resulted from mixed species schooling during spawning periods. It is thought that hybridisation is more likely if one or both parent species is rare in an area, which is the case in much of the Main Hawaiian Islands, where overfishing
has severely depleted all trevally species populations.
s, with the popularity of the fish leading to extensive aquaculture
trials. The catch statistics for the bluefin trevally are poorly reported in most of its range, with only parts of the western Indian Ocean supplying information to the FAO
. In this region, catch levels have fluctuated between 2 and 50 tonne
s in the past decade. Hawaii also keeps catch records, with these showing the species is taken in far less numbers than the giant trevally, with only 704 pounds taken compared to 10 149 lbs of giant trevally in 1998. In Hawaii, the nearshore stocks of the species have been in decline since the early 1900s, with commercial landings dropping over 300% from 1990 to 1991, and have not recovered. Most bluefin trevally sold in Hawaii are now imported from other Indo-Pacific nations. The species is taken by a variety of netting and trapping methods, as well and by hook and line in commercial fisheries. It is usually sold fresh, as well as frozen or salted
. The rapid decline in the population has seen a focus on breeding the bluefin trevally in captivity. The species' aquaculture potential was first investigated in a 1975 experiment in French Polynesia
, where juveniles of the species were caught in the wild and transported back to a laboratory. The study found the fish grew to a commercial size of 300 g in 6 to 8 months and only suffered a 5% mortality rate
. It was concluded that such a technique carried out on a larger scale in lagoons would be promising due to the growth rate and relatively high price commanded by the species at market
. Further investigations into the potential for offshore aquaculture were conducted in Hawaii, where the species successfully spawned in captivity. The only barrier in these studies to successful production was problems with commercial food items. An in vitro
cell culture
has recently been established for the species, which will allow long term management of potential viral diseases that may arise during aquaculture of the fish.
The bluefin trevally is one of the premier gamefish of the Indo-Pacific region, although is often overshadowed by its larger cousin, the giant trevally. The fish makes long powerful runs on light tackle, and is a determined fighter. The species readily accepts both bait
and lures
, with live fish or squid often used as bait and a variety of lures also used on the species. Lures may include poppers, plugs, spoons, jigs, soft plastic lures and even saltwater flies
. The species inshore habits make it a popular target for spearfishermen
also. In Hawaii the species has bag and size limit restrictions in place to prevent further overexploitation
. It is considered to be a good to excellent food fish
, however many cases of ciguatera
poisoning have been attributed to the bluefin trevally. Laboratory tests have confirmed the presence of the toxin in the species flesh, with fish greater than 50 cm likely to be a carrier. The risk of poisoning has also affected the sales of the fish in the marketplace in recent years. Also of concern is one report of infection by a dracunculoid
parasite while preparing the fish for eating. In this case, the parasite invaded the victim's body by entering an open wound
while he was fillet
ing the species, and is believed to be one of the first records for such cross contamination. The bluefin trevally has been successfully kept in large saltwater aquaria, but require large water volumes to adapt well.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of large, widely distributed marine
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
classified in the jack family, Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
. The bluefin trevally is distributed throughout the tropical waters of the Indian
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, ranging from Eastern Africa in the west to Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
in the east, including Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
in the north and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in the south. The species grows to a maximum known length of 117 cm and a weight of 43.5 kg
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
, however is rare above 80 cm. Bluefin trevally are easily recognised by their electric blue
Electric blue (color)
Electric blue is a color close to cyan that is a representation of the color of lightning, an electric spark, and argon signs; it is named after the ionized air glow produced during electrical discharges....
fins, tapered snout and numerous blue and black spots on their sides. Juveniles lack these obvious colours, and must be identified by more detailed anatomical features such as fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
ray and scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
counts. The bluefin trevally inhabits both inshore environments such as bays, lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s and shallow reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, as well as deeper offshore reefs, atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
s and bomboras. Juveniles prefer shallower, protected waters, even entering estuaries for short periods in some locations.
The bluefin trevally is a strong predatory fish, with a diet dominated by fish and supplemented by cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s as an adult. Juveniles consume a higher amount of small crustaceans, but transfer to a more fish based diet as they grow. The species displays a wide array of hunting techniques ranging from aggressive midwater attacks, reef ambush
Ambush
An ambush is a long-established military tactic, in which the aggressors take advantage of concealment and the element of surprise to attack an unsuspecting enemy from concealed positions, such as among dense underbrush or behind hilltops...
es and foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...
interactions with other larger species, snapping up any prey items missed by the larger animal. The bluefin trevally reproduces at different periods throughout its range, and reaches sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at 30–40 cm in length and around 2 years of age. It is a multiple spawner
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
, capable of reproducing up to 8 times per year, releasing up to 6 million eggs per year in captivity. Growth is well studied, with the fish reaching 194 mm in its first year, 340 mm in the second and 456 mm in the third year. The bluefin trevally is a popular target for both commercial
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
and recreational fishermen
Angling
Angling is a method of fishing by means of an "angle" . The hook is usually attached to a fishing line and the line is often attached to a fishing rod. Fishing rods are usually fitted with a fishing reel that functions as a mechanism for storing, retrieving and paying out the line. The hook itself...
. Commercial fisheries record up to 50 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s of the species taken per year in the west Indian Ocean, and around 700 lbs per year in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. The rapid decimation of the Hawaiian population due to overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
has led to increased research in the aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
potential of the species, with spawning achieved in captivity. Despite its popularity as a table fish, many cases of ciguatera
Ciguatera
Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...
poisoning have been reported from the species.
Taxonomy and phylogeny
The bluefin trevally is classified within the genus CaranxCaranx
Caranx is a genus of tropical to subtropical marine fish in the jack family Carangidae, commonly known as jacks, trevallies and kingfishes. They are moderate to large sized, deep bodied fishes which are distinguished from other carangid genera by specific gill raker, fin ray and dentition...
, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae
Carangidae
Carangidae is a family of fish which includes the jacks, pompanos, jack mackerels, and scads.They are marine fish found in the Atlantic, Indian and Pacific Oceans...
, a group of percoid
Percoidei
Percoidei is one of eighteen suborders of bony fish in the order Perciformes. Many commercially harvested fish species are contained in this suborder, including the snappers, jacks, whitings, groupers, bass, perches and porgies.-Divisions:...
fishes in the order Perciformes
Perciformes
The Perciformes, also called the Percomorphi or Acanthopteri, is one of the largest orders of vertebrates, containing about 40% of all bony fish. Perciformes means perch-like. They belong to the class of ray-finned fish and comprise over 7,000 species found in almost all aquatic environments...
.
The species was first scientifically described by the famed French naturalist
Naturalist
Naturalist may refer to:* Practitioner of natural history* Conservationist* Advocate of naturalism * Naturalist , autobiography-See also:* The American Naturalist, periodical* Naturalism...
Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
in 1833 based on specimens collected off Waigio, Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
; one of which was designated to be the holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
. He named the species Caranx melampygus, placing the species in the jack genus Caranx which had been established by Bernard Lacépède three decades previously. The name's specific epithet is derived from the Latin translation of "black spotted". This is still currently considered the correct placement, however later authors placed in other now defunct genera (Carangus and Carangichthys) which has since been deemed incorrect, and the original classification stands. The species was independently redescribed and named seven times after Cuvier's initial description, with all of these names assigned between 1836 and 1895. The names C. bixanthopterus and C. stellatus were often used in the literature, and were variably classed as synonyms
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
of C. melampygus or valid individual species after their naming. This confusion culminated in Yojiro Wakiya concluding in 1924 they should be treated as separate species. The taxonomy of the species was finally revised by Frederick Berry in 1965, who resolved these two names as being synonymous with C. melampygus, and placed several other names in synonymy with C. melampygus. Under ICZN
International Code of Zoological Nomenclature
The International Code of Zoological Nomenclature is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals...
nomenclature rules, these later names are deemed junior synonyms of C. melampygus and rendered invalid. The species hat not been included in any detailed phylogenetic studies of the Carangidae.
The species is most commonly
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
referred to as the 'bluefin trevally', with the species's distinctive blue fins contributing to most of its other common names. These include bluefin jack, bluefin kingfish, blue ulua, omilu, bluefinned crevalle and spotted trevally. The species has many other non-English names due to its wide distribution.
Description
The bluefin trevally is a large fish, growing to a maximum known length of 117 cm and a weight of 43.5 kg, however it is rare at lengths greater than 80 cm. It is similar in shape to a number of other large jacks and trevallies, having an oblong, compressed body with the dorsal profile slightly more convex than the ventral profile, particularly anteriorly. This slight convexity leads to the species having a much more pointed snout than most other members of Caranx. The dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
is in two parts, the first consisting of 8 spines and the second of 1 spine followed by 21 to 24 soft rays. The anal fin consists of 2 anteriorly detached spines followed by 1 spine and 17 to 20 soft rays. The pelvic fins contain 1 spine and 20 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
has a pronounced and moderately long anterior arch, with the curved section intersecting the straight section below the lobe of the second dorsal fin. The curved section of the lateral line contains 55-70 scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
while the straight section contains 0 to 10 scales followed by 27 to 42 strong scute
Scute
A scute or scutum is a bony external plate or scale, as on the shell of a turtle, the skin of crocodilians, the feet of some birds or the anterior portion of the mesonotum in insects.-Properties:...
s. The chest is completely covered in scales. The upper jaw contains a series of strong outer canine
Canine tooth
In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
s with an inner band of smaller teeth, while the lower jaw contains a single row of widely spaced conical teeth. The species has 25 to 29 gill raker
Gill raker
Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch and are involved with filter feeding tiny prey. They are not to be confused with the gill filaments that compose the bony part of the gill. Rakers are usually present in two rows, projecting from both the...
s in total and there are 24 vertebrae present. The eye is covered by a moderately weakly developed adipose eyelid, and the posterior extremity of the jaw
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
is vertically under or just past the anterior margin of the eye. Despite their wide range, the only geographical variation in the species is the depth of the body in smaller specimens.
The upper body of the bluefin trevally is a silver-brassy colour, fading to silvery white on the underside of the fish, often with blue hues. After they reach lengths greater than 16 cm, blue-black spots appear on the upper flanks of the fish, with these becoming more prolific with age. There is no dark spot on the operculum
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....
. The species takes its name from the colour of its dorsal, anal and caudal fins, which are a diagnostic electric blue
Electric blue (color)
Electric blue is a color close to cyan that is a representation of the color of lightning, an electric spark, and argon signs; it is named after the ionized air glow produced during electrical discharges....
. The pelvic and pectoral fins are white, with the pectoral fin having a yellow tinge. Juvenile fish do not have the bright blue fins, instead have dark fins with the exception of a yellow pectoral fin. Some juvenile fish have also been recorded as having up to five dark vertical bars on their sides.
Distribution
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, ranging along the coasts of four continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
s and hundreds of smaller islands and archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
s. In the Indian Ocean, the species easternmost range is the coast of continental Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, being distributed from the southern tip of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
north along the east African coastline to the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
and Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
. The species' range extends eastwards along the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n coastline including Pakistan
Pakistan
Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
and into South East Asia, the Indonesian Archipelago
Malay Archipelago
The Malay Archipelago refers to the archipelago between mainland Southeastern Asia and Australia. The name was derived from the anachronistic concept of a Malay race....
and northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The southernmost record from the west coast of Australia comes from Exmouth Gulf
Exmouth Gulf
Exmouth Gulf is a gulf in the north west of Western Australia. It lies between North West Cape and the main coastline of Western Australia. It is considered to be part of the region of the North West Shelf and in the Canning Basin area.-Environment:...
. Elsewhere in the Indian Ocean, the species has been recorded from hundreds of small island groups including the Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
, Seychelles
Seychelles
Seychelles , officially the Republic of Seychelles , is an island country spanning an archipelago of 115 islands in the Indian Ocean, some east of mainland Africa, northeast of the island of Madagascar....
, Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and the Cocos (Keeling) Islands
Cocos (Keeling) Islands
The Territory of the Cocos Islands, also called Cocos Islands and Keeling Islands, is a territory of Australia, located in the Indian Ocean, southwest of Christmas Island and approximately midway between Australia and Sri Lanka....
.
The bluefin trevally is abundant in the central Indo-Pacific region, found throughout all the archipelagos and offshore islands including Indonesia, Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
and Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
. Along continental Asia, the species has been recorded from Malaysia to Vietnam
Vietnam
Vietnam – sometimes spelled Viet Nam , officially the Socialist Republic of Vietnam – is the easternmost country on the Indochina Peninsula in Southeast Asia. It is bordered by China to the north, Laos to the northwest, Cambodia to the southwest, and the South China Sea –...
and mainland China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
. Its offshore range does extend north to Hong Kong
Hong Kong
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
, Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...
and southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
in the north western Pacific. In the south, the species reaches as far south as Sydney in Australia. Its distribution continues throughout the western Pacific including Tonga
Tonga
Tonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
, Western Samoa and Polynesia
Polynesia
Polynesia is a subregion of Oceania, made up of over 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are termed Polynesians and they share many similar traits including language, culture and beliefs...
, and the Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
an Islands. The easternmost limit of the species distribution is the Mesoamerica
Mesoamerica
Mesoamerica is a region and culture area in the Americas, extending approximately from central Mexico to Belize, Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica, within which a number of pre-Columbian societies flourished before the Spanish colonization of the Americas in the 15th and...
n coastline between Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
and Ecuador
Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...
in the central eastern Pacific, including islands such as the Galapogos.
Habitat
The bluefin trevally occurs in a wide range of inshore and offshore marine settings throughout its range, including estuarine waters. The species is known to move throughout the water column; however is most often observed in a demersal setting, swimming not far from the seabed. In the inshore environment, the species is present in almost all settings including bays, harbours, coralCoral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
and rocky reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
s, lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s, sand flats and seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows.
Juveniles and subadults are more common in these settings, and prefer these more protected environments, where they live in water to a minimum of around 2 m depth. Adults tend to prefer more exposed, deeper settings such as outer reef slopes, outlying atoll
Atoll
An atoll is a coral island that encircles a lagoon partially or completely.- Usage :The word atoll comes from the Dhivehi word atholhu OED...
s and bomboras, often near drop offs, with the species reported from depths up to 183 m. Adults often enter shallower channel
Channel (geography)
In physical geography, a channel is the physical confine of a river, slough or ocean strait consisting of a bed and banks.A channel is also the natural or human-made deeper course through a reef, sand bar, bay, or any shallow body of water...
s, reefs and lagoons to feed at certain periods during the day. The bluefin trevally displays some habitat partitioning with giant trevally
Giant trevally
The giant trevally, Caranx ignobilis , is a species of large marine fish classified in the jack family, Carangidae...
, Caranx ignobilis, tending to be more common outside the major bays than their relatives.
Juvenile and subadult bluefin trevally have been recorded in estuaries in several locations, and generally occupy large, open estuaries up to the middle reaches of the system. These estuaries are often lined by mudflats and mangrove
Mangrove
Mangroves are various kinds of trees up to medium height and shrubs that grow in saline coastal sediment habitats in the tropics and subtropics – mainly between latitudes N and S...
s, however the species rarely enters these shallow waters. Individuals of between 40 and 170 mm have been recorded in South African estuaries, where they are the least tolerant carangid to the brackish and freshwater conditions of these systems. Bluefin trevally can tolerate salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
of between 6.0 to 35 ‰, and only occupy clear, low turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
waters. There is evidence the species is only resident in these estuaries for short periods. The species is also absent from coastal lakes that many other carangids are known from.
Biology and ecology
The bluefin trevally is a schoolingShoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
species as a juvenile, transitioning to a more solitary fish with well defined home range
Home range
Home range is the area where an animal lives and travels in. It is closely related to, but not identical with, the concept of "territory".The concept that can be traced back to a publication in 1943 by W. H. Burt, who constructed maps delineating the spatial extent or outside boundary of an...
s as an adult. Adults do school to form spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
aggregations or temporarily while hunting, with evidence from laboratory studies indicates bluefin trevally are able to coordinate these aggregations over coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s based on the release of dimethylsulfoniopropionate
Dimethylsulfoniopropionate
Dimethylsulfoniopropionate , is an organosulfur compound with the formula 2S+CH2CH2COO−. This zwitterionic metabolite found in marine phytoplankton, seaweeds, and some species of terrestrial and aquatic vascular plants...
(DMSP) from the reef. DMSP is a naturally occurring chemical produced by marine algae and to a lesser extent coral
Coral
Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...
s and their symbiotic zooxanthellae. The number of fish present in an area is also influenced by tidal
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
factors and possibly the abundance of prey and other environmental factors. Tracking studies in Hawaii have found bluefin trevally patrol
Patrol
A patrol is commonly a group of personnel, such as police officers or soldiers, that are assigned to monitor a specific geographic area.- Military :...
back and forth along a home range of patch reef walls during the day, only stopping for variable periods where major depth changes or discontinuities in the reef were present. Several fish patrol the same reef patch, reversing direction where the others do. While most fish patrol the one reef, some have been observed to make excursions to nearby reefs, before returning to their home reef later. Night
Night
Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...
time movements are less extensive than daytime movements, with the trevally moving rapidly between several small reef sections, before slowing down and milling in one patch for around an hour. The fish living in a particular region congregate in one area at night, before returning to their individual daytime range during the day. The reason for this congregation is unclear, but may be important to the social structure of the species. Long term studies have found the fish may range up to 10.2 km over several months, however is much less restricted in its movements than its relative, the giant trevally. A Hawaiian biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
study found the species to be one of the most abundant large predators in the islands, however it is less abundant in the heavily exploited Main Hawaiian Islands compared to the remote Northwest Hawaiian Islands. The main difference in these populations was the relative lack of large adult fish in the inhabited areas compared to the remote, unfished regions. A study on carangids caught during a fishing tournament
Fishing tournament
A fishing tournament, or derby, is an organised competition among anglers. Fishing tournaments typically take place as a series of competitive events around or on a clearly defined body of water with specific rules applying to each event...
in Hawaii found the bluefin trevally is the most common trevally species taken, accounting for over 80% of the carangid catch. The authors note that this may not only reflect its abundance, but also it vulnerability to specific fishing methods used in the tournament. Apart from the typical predator-prey relationship the species shows (described later), an individual of the species has been seen to rub itself against the skin of a Galapagos shark
Galapagos shark
The Galapagos shark is a species of requiem shark, family Carcharhinidae, found worldwide. This species favors clear reef environments around oceanic islands, where it is often the most abundant shark species...
, apparently to rid itself of parasites. This behaviour is also observed in rainbow runner
Rainbow runner
The rainbow runner , also known as the rainbow yellowtail, Spanish jack and Hawaiian salmon, is a common species of pelagic marine fish of the jack family, Carangidae. The species is widespread throughout the tropical and subtropical waters of the world, inhabiting both coastal as well as far...
and is a rare example of a commensal cleaner relationship where the cleaner does not gain anything.
Diet and feeding
Priacanthidae
Priacanthidae is a family of fish, common name bigeye, comprising 18 species of marine fishes. "Catalufa" is an alternate common name for some members of the priacanthidae family. The etymology of the scientific name refers to the family's very rough, spined scales...
being the most common. Despite the preference of several families, bluefin trevally do take a very wide variety of fish in small amounts, including various species of eel
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
. The species appears to have a preference for fish of a specific size, which depends on its own length and age.
Cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s (mainly octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
or squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
) and a wide array of crustaceans are also taken in smaller quantities, with shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s, stomatopods and crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s being the most common. The diet of juveniles in Hawaiian and South African estuaries has also been determined, with these younger fish having a more crustacean based diet than the adults. In Hawaii, crustaceans make up 96% of the gut contents numerically, with tanaids and isopods dominating the diet, while fish (mainly gobioids
Goby
The gobies form the family Gobiidae, which is one of the largest families of fish, with more than 2,000 species in more than 200 genera. Most are relatively small, typically less than 10 cm in length...
) only make up 4% numerically. Juveniles less than 170 mm in South African estuaries feed predominantly on mysids and paenid prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s, before shifting to a more fish based diet at larger sizes. Small fish are able to effectively filter these small crustaceans from the water, while adults are not. In both cases, a transition to a more fish based diet with age was found to occur, although the length at which this transition occurred varied between location. The diet overlap with the similar C. ignobilis is low in the Hawaiian Islands, suggesting there is some separation of feeding niches. Calculations suggest each individual bluefin trevally consumes around 45 kg of fish per year on average, making it one of the most effective predators in this habitat.
The bluefin trevally displays a remarkable array of hunting techniques, ranging from midwater attacks to ambush and taking advantage of larger forage fish
Forage fish
Forage fish, also called prey fish or bait fish, are small fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed near the base of the food chain on plankton, often by filter feeding...
. The species is reported to hunt during the day, particularly at dawn
Dawn
Dawn is the time that marks the beginning of the twilight before sunrise. It is recognized by the presence of weak sunlight, while the sun itself is still below the horizon...
and dusk
Dusk
Dusk is the beginning of darkness in the evening, and occurs after twilight, when the sky generally remains bright and blue. Civil dusk is when the earth has rotated enough that the center of the sun is at 6° below the local horizon...
in most locations; however it is known to be a nocturnal feeder in South Africa. The bluefin trevally hunts both as a solitary individual and in groups of up to 20, with most fish preferring an individual approach. In groups, these fish will rush their prey, and disperse the school, allowing for isolated individuals to be picked out and eaten, much in the way the related species, giant trevally have been observed to do in captivity. In some cases, only one individual in a group will attack the prey school. Where the prey is schooling reef fishes, once the prey school has been attacked, the trevally chases down the prey as they scatter back to cover in the corals, often colliding with coral as they attempt to snatch a fish. While hunting in midwater, fish swim both against and with the tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
, although significantly more fish hunt when swimming with the tide (i.e. 'downstream'), suggesting some mechanical advantage is gained when hunting in this mode. Another method of attack is ambush
Ambush
An ambush is a long-established military tactic, in which the aggressors take advantage of concealment and the element of surprise to attack an unsuspecting enemy from concealed positions, such as among dense underbrush or behind hilltops...
; in this mode the trevally change their colour to a dark pigmentation state and hide behind large coral lumps close to where the aggregations (often spawning reef fish) occur. Once the prey is close enough to the hiding spot, the fish ram the base of the school, before chasing down individual fish. These dark fish in ambush mode vigorously drive away any other bluefin trevally that stray too close to the aggregation. Ambushes have also been observed on small midwater planktivorous fishes are moving to or from the shelter of the reef. In many cases, the species uses changes in the depth of the reef such as ledges to conceal its ambush attacks. Bluefin trevally also enter lagoons as the tide rises to hunt small baitfish in the shallow confines, leaving as the tide falls. The species is also known to follow large rays
Stingray
The stingrays are a group of rays, which are cartilaginous fishes related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes, and consist of eight families: Hexatrygonidae , Plesiobatidae , Urolophidae , Urotrygonidae , Dasyatidae , Potamotrygonidae The...
, shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and other foraging fish such as goatfish
Goatfish
Goatfishes are tropical marine perciform fish of the family Mullidae. Seldom found in brackish waters, goatfish are most associated with the reefs of the Atlantic, Indian, and Pacific Oceans...
and wrasse
Wrasse
The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 82 genera, which are divided into nine subgroups or tribes....
around sandy substrates, waiting to pounce on any disturbed crustaceans or fish which are flushed out by the larger fish.
Life history
The bluefin trevally reaches sexual maturitySexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at between 30 and 40 cm in length and around 2 years in age,
with one study Hawaii suggesting maturation occurs at a length of around 35 cm on average. There is also a difference in the length at maturation between the two sexes, with females on average reaching maturity at 32.5 cm length, while males attain maturity at 35 cm on average. Sex ratio
Sex ratio
Sex ratio is the ratio of males to females in a population. The primary sex ratio is the ratio at the time of conception, secondary sex ratio is the ratio at time of birth, and tertiary sex ratio is the ratio of mature organisms....
s in the species vary by location with population off east Africa being skewed towards males (M:F = 1.68:1), while in Hawaii the opposite is true with the M:F ratio being 1:1.48. The period of the year over which spawning
Spawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
occurs is also variable by location, with African fish reproducing between September and March while in Hawaii this occurs between April and November, with a peak in May to July. Natural spawning behaviour in the species has never been observed, although large aggregations of bluefin trevally observed in Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...
consisting of over 1000 fish are believed to be for the purpose of spawning. Extensive studies on the species in captivity has revealed the species to be a multiple spawner, capable of spawning at least 8 times a year, and up to twice in 5 days. Spawning events are often clustered in a few consecutive or alternate days, usually in the third or fourth lunar phase
Lunar phase
A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
s. Spawning apparently occurs at night to minimise predation on egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s. Fecundity
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
in the natural environment has been reported to range from around 50 000 to 4 270 000, with larger individuals releasing more eggs. Studies in captive fish show females may produce over 6 000 000 eggs per year. These eggs are pelagic and spherical, with diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...
s between 0.72 and 0.79 mm.
The development of the bluefin trevally larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
after hatching has been briefly described in a study of changes in the digestive enzyme
Digestive enzyme
'Digestive enzymes' are enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption by the body. Digestive enzymes are found in the digestive tract of animals where they aid in the digestion of food as well as inside the cells,...
s of the species. The species has depleted its storage of energy from the egg at 3 days old, with a series of transformations including coiling of the gut and fin formation occurring before flexion
Flexion
In anatomy, flexion is a position that is made possible by the joint angle decreasing. The skeletal and muscular systems work together to move the joint into a "flexed" position. For example the elbow is flexed when the hand is brought closer to the shoulder...
at 26 days of age. Digestive enzymes active from hatching to 30 days old show an apparent shift from carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
utilisation to protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
and lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
utilisation as the larvae grows older. Measurements from juveniles in Hawaii indicate the fish is around 70 mm by 100 days and 130 mm by 200 days. Otolith data fitted to the von Bertalanffy growth curve shows the species grows to 194 mm in its first year, 340 mm in the second and 456 mm in the third year. It reaches 75 cm by 8 years of age and 85 cm by 12 years. This model also suggests a growth of 0.45 mm/day; while laboratory feeding studies found the fish grow at an average of 0.4 mm/day in these confined conditions. The maximum theoretical size indicated from the growth curves is 89.7 cm, much less than the 117 cm reported as the known maximum size. Juveniles often enter estuaries, however the species is not estuary dependant as breeding is known to occur where no estuaries are present, suggesting the use of these habitats is facultative
Facultative
Facultative means "optional" or "discretionary" , used mainly in biology in phrases such as:* Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production...
. The fish move from these shallower inshore waters to deeper reefs as they grow.
Two hybridisation events in the species are known from Hawaii; the first with the giant trevally, Caranx ignobilis and the second with the bigeye trevally
Bigeye trevally
The bigeye trevally, Caranx sexfasciatus , is a species of widespread large marine fish classified in the jack family Carangidae...
, Caranx sexfasciatus. Both were initially identified as hybrids by intermediate physical characteristics, and were later confiremed by DNA sequencing
DNA sequencing
DNA sequencing includes several methods and technologies that are used for determining the order of the nucleotide bases—adenine, guanine, cytosine, and thymine—in a molecule of DNA....
. It has been suggested these hybrids resulted from mixed species schooling during spawning periods. It is thought that hybridisation is more likely if one or both parent species is rare in an area, which is the case in much of the Main Hawaiian Islands, where overfishing
Overfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
has severely depleted all trevally species populations.
Relationship to humans
The bluefin trevally is an important species to both commercial fisheries and anglerAngling
Angling is a method of fishing by means of an "angle" . The hook is usually attached to a fishing line and the line is often attached to a fishing rod. Fishing rods are usually fitted with a fishing reel that functions as a mechanism for storing, retrieving and paying out the line. The hook itself...
s, with the popularity of the fish leading to extensive aquaculture
Aquaculture
Aquaculture, also known as aquafarming, is the farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants. Aquaculture involves cultivating freshwater and saltwater populations under controlled conditions, and can be contrasted with commercial fishing, which is the...
trials. The catch statistics for the bluefin trevally are poorly reported in most of its range, with only parts of the western Indian Ocean supplying information to the FAO
Fão
Fão is a town in Esposende Municipality in Portugal....
. In this region, catch levels have fluctuated between 2 and 50 tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s in the past decade. Hawaii also keeps catch records, with these showing the species is taken in far less numbers than the giant trevally, with only 704 pounds taken compared to 10 149 lbs of giant trevally in 1998. In Hawaii, the nearshore stocks of the species have been in decline since the early 1900s, with commercial landings dropping over 300% from 1990 to 1991, and have not recovered. Most bluefin trevally sold in Hawaii are now imported from other Indo-Pacific nations. The species is taken by a variety of netting and trapping methods, as well and by hook and line in commercial fisheries. It is usually sold fresh, as well as frozen or salted
Salting (food)
Salting is the preservation of food with dry edible salt. It is related to pickling . It is one of the oldest methods of preserving food, and two historically significant salt-cured foods are dried and salted cod and salt-cured meat.Salting is used because most bacteria, fungi and other potentially...
. The rapid decline in the population has seen a focus on breeding the bluefin trevally in captivity. The species' aquaculture potential was first investigated in a 1975 experiment in French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
, where juveniles of the species were caught in the wild and transported back to a laboratory. The study found the fish grew to a commercial size of 300 g in 6 to 8 months and only suffered a 5% mortality rate
Mortality rate
Mortality rate is a measure of the number of deaths in a population, scaled to the size of that population, per unit time...
. It was concluded that such a technique carried out on a larger scale in lagoons would be promising due to the growth rate and relatively high price commanded by the species at market
Market
A market is one of many varieties of systems, institutions, procedures, social relations and infrastructures whereby parties engage in exchange. While parties may exchange goods and services by barter, most markets rely on sellers offering their goods or services in exchange for money from buyers...
. Further investigations into the potential for offshore aquaculture were conducted in Hawaii, where the species successfully spawned in captivity. The only barrier in these studies to successful production was problems with commercial food items. An in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
has recently been established for the species, which will allow long term management of potential viral diseases that may arise during aquaculture of the fish.
The bluefin trevally is one of the premier gamefish of the Indo-Pacific region, although is often overshadowed by its larger cousin, the giant trevally. The fish makes long powerful runs on light tackle, and is a determined fighter. The species readily accepts both bait
Fishing bait
Fishing bait is any substance used to attract and catch fish, e.g. on the end of a fishing hook, or inside a fish trap. Traditionally, nightcrawlers, insects, and smaller bait fish have been used for this purpose...
and lures
Fishing lure
A fishing lure is an object attached to the end of a fishing line which is designed to resemble and move like the prey of a fish. The purpose of the lure is to use movement, vibration, and colour to catch the fish's attention so it bites the hook...
, with live fish or squid often used as bait and a variety of lures also used on the species. Lures may include poppers, plugs, spoons, jigs, soft plastic lures and even saltwater flies
Fly fishing
Fly fishing is an angling method in which an artificial 'fly' is used to catch fish. The fly is cast using a fly rod, reel, and specialized weighted line. Casting a nearly weightless fly or 'lure' requires casting techniques significantly different from other forms of casting...
. The species inshore habits make it a popular target for spearfishermen
Spearfishing
Spearfishing is an ancient method of fishing that has been used throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks....
also. In Hawaii the species has bag and size limit restrictions in place to prevent further overexploitation
Overexploitation
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Sustained overexploitation can lead to the destruction of the resource...
. It is considered to be a good to excellent food fish
Fish (food)
Fish is a food consumed by many species, including humans. The word "fish" refers to both the animal and to the food prepared from it. Fish has been an important source of protein for humans throughout recorded history.-Terminology:...
, however many cases of ciguatera
Ciguatera
Ciguatera is a foodborne illness caused by eating certain reef fishes whose flesh is contaminated with toxins originally produced by dinoflagellates such as Gambierdiscus toxicus which lives in tropical and subtropical waters. These dinoflagellates adhere to coral, algae and seaweed, where they are...
poisoning have been attributed to the bluefin trevally. Laboratory tests have confirmed the presence of the toxin in the species flesh, with fish greater than 50 cm likely to be a carrier. The risk of poisoning has also affected the sales of the fish in the marketplace in recent years. Also of concern is one report of infection by a dracunculoid
Camallanida
The Camallanida are an order of nematodes.* Parasites of terrestrial and aquatic vertebrates* Copepods as obligatory secondary hostsThey are sometimes included in the Spirurida as a suborderCamallanina....
parasite while preparing the fish for eating. In this case, the parasite invaded the victim's body by entering an open wound
Wound
A wound is a type of injury in which skin is torn, cut or punctured , or where blunt force trauma causes a contusion . In pathology, it specifically refers to a sharp injury which damages the dermis of the skin.-Open:...
while he was fillet
Fillet (cut)
A fillet is a cut or slice of boneless meat or fish.- Meat :In the case of beef, in the USA, the term most often refers to beef tenderloin, especially filet mignon.- Chicken :...
ing the species, and is believed to be one of the first records for such cross contamination. The bluefin trevally has been successfully kept in large saltwater aquaria, but require large water volumes to adapt well.