Sharptail mola
Encyclopedia
The sharptail mola, Masturus lanceolatus, is a species of mola
found circumglobally in tropical and temperate
waters. It is similar in appearance to the ocean sunfish
(Mola mola), but can be distinguished by the projection on its clavus (pseudo-tail). Other common name
s include sharpfin sunfish, point-tailed sunfish, and trunkfish. Rarely encountered, very little is known of the biology or life history of the sharptail mola. It has recently become important to commercial fisheries
operating off eastern Taiwan
.
moved an average of 10 km (6 mi) a day.
s are fused into beak
-like plates. The dorsal
and anal fins are placed posteriorly, and the base of the dorsal fin is longer than that of the anal fin. In place of a caudal fin, the dorsal and anal fins merge into a clavus, formed by 18-20 fin rays. The central rays in the clavus are supported by the last vertebra and form an elongated triangular lobe; some authors believe these rays to be remnants of the larval caudal fin, though this is disputed.
The skin
is covered with small dermal denticles that are finer than those of the ocean sunfish. The coloration is silvery with the upper parts of the sides grayish brown to blackish. The sides may bear ill-defined dark spots. The dorsal and anal fins are slaty, while the clavus may have pale blotches. This species is distinguished from the similar Masturus oxyuropterus by its prominent chin, the lack of a concavity above the eyes, and the unequal lengths of the dorsal and anal fin bases. Fraser-Brunner proposed that these two forms may represent different sexes of the same species.
Robert Collett
, who examined some of the first known specimens of sharptail mola, speculated that they might represent abnormal ocean sunfishes that had retained larval characteristics. However, it is now known that the caudal projection is a secondary development that follows the loss of the primary tail
. The swimming mode of the sharptail is similar to that of other ocean sunfishes, using sculling motions of its long dorsal and anal fins to propel itself through the water. The anal fin moves more extensively than the dorsal fin. The small pectoral fins move constantly to control pitch, while the clavus is employed as a rudder
.
Juvenile sharptail molas are known to feed on benthic annelid
s and sponges. Adults likely feed on medusa
e, siphonophores, ctenophore
s, and salp
s, as well as some fish
es, crustacean
s, and molluscs. Sharptail molas sometimes have remora
s attached to the surface of their bodies or inside the buccal cavity. In 1949, a sharptail mola off North Carolina
was found with a common remora (Remora remora) wedged inside the gill arches on its right side. This evidently impaired the respiration
of the mola, such that it foundered on the beach and was collected by fishermen.
Molas are oviparous and are amongst the most fecund of all fishes. Larva
l sharptail molas are rounded in shape and develop large pyramidal dermal spines over the body, which persist through a prejuvenile phase called the "Molacanthus" stage. In this stage, the body is deep and compressed, with a thin keel-like structure below the abdominal region. This ridge is made from skin and covered with several rows of small spines. The skin is rough, being covered with small prickles. The spines eventually diminish in size and disappear, leaving scars obvious on the sides of young fish up to 70 mm (2.8 in) long. Their coloration is dark brown on the back, becoming very light on the sides and belly. The lifespan
for this species is estimated to be 85 years for males and 105 years for females.
, Taiwan has increased demand for the meat of the sunfish (called "mambo fish" after a public vote), whereas before only the intestine
s and reproductive organs were sold while the rest of the fish was discarded. The month-long April festival draws some 120,000 visitors and features "101 ways to eat" sunfish. Consequently, catches of sunfishes off eastern Taiwan have risen sharply, with the sharptail mola comprising 90% of the catch. In 2005, 208 tonnes were landed and the annual sunfish catch was valued at one million USD. The species is caught by set net, drift net, and longline fisheries. The impact of this increased exploitation on sunfish stocks is under investigation.
Molidae
Molidae is the family of the molas or ocean sunfishes, unique fish whose bodies come to an end just behind the dorsal and anal fins, giving them a "half-a-fish" appearance...
found circumglobally in tropical and temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
waters. It is similar in appearance to the ocean sunfish
Ocean sunfish
The ocean sunfish, Mola mola, or common mola, is the heaviest known bony fish in the world. It has an average adult weight of . The species is native to tropical and temperate waters around the globe. It resembles a fish head with a tail, and its main body is flattened laterally...
(Mola mola), but can be distinguished by the projection on its clavus (pseudo-tail). Other common name
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...
s include sharpfin sunfish, point-tailed sunfish, and trunkfish. Rarely encountered, very little is known of the biology or life history of the sharptail mola. It has recently become important to commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
operating off eastern 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...
.
Distribution and habitat
The distribution of this sharptail mola is worldwide in tropical and temperate waters. They are primarily inhabitants of the epipelagic zone but are rarely sighted at the surface, many of those appearing to be ill and parasite-ridden. During the day, they spend most of their time at a depth of 5–200 meters (16–660 ft), preferring water temperatures above 20°C but making repeated dives into cooler, deeper water, possibly to feed or to avoid predators. At night, they spend most of their time between 100–250 meters (330–820 ft). They have been sighted in the mesopelagic zone to a depth of 670 meters (2,200 ft), but may descend to over 1,000 meters (3,280 ft). One tagged individual in the Gulf of MexicoGulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
moved an average of 10 km (6 mi) a day.
Description
One of the largest bony fishes, the sharptail mola can measure up to 3.4 meters (11 ft) long and weigh 2,000 kg (4,410 lbs). It has an oval body with an evenly convex forehead profile. The eyes are placed more forward on the head than in the genus Mola. The teeth in both jawJaw
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...
s are fused into beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
-like plates. The dorsal
Dorsal 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...
and anal fins are placed posteriorly, and the base of the dorsal fin is longer than that of the anal fin. In place of a caudal fin, the dorsal and anal fins merge into a clavus, formed by 18-20 fin rays. The central rays in the clavus are supported by the last vertebra and form an elongated triangular lobe; some authors believe these rays to be remnants of the larval caudal fin, though this is disputed.
The skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
is covered with small dermal denticles that are finer than those of the ocean sunfish. The coloration is silvery with the upper parts of the sides grayish brown to blackish. The sides may bear ill-defined dark spots. The dorsal and anal fins are slaty, while the clavus may have pale blotches. This species is distinguished from the similar Masturus oxyuropterus by its prominent chin, the lack of a concavity above the eyes, and the unequal lengths of the dorsal and anal fin bases. Fraser-Brunner proposed that these two forms may represent different sexes of the same species.
Biology and ecology
Robert Collett
Robert Collett was a Norwegian zoologist. He worked with vertebrates, primarily fishes. From 1864 he was curator at the Zoological Museum in Oslo. In 1882 he became its director and from 1884 was a professor there...
, who examined some of the first known specimens of sharptail mola, speculated that they might represent abnormal ocean sunfishes that had retained larval characteristics. However, it is now known that the caudal projection is a secondary development that follows the loss of the primary tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
. The swimming mode of the sharptail is similar to that of other ocean sunfishes, using sculling motions of its long dorsal and anal fins to propel itself through the water. The anal fin moves more extensively than the dorsal fin. The small pectoral fins move constantly to control pitch, while the clavus is employed as a rudder
Rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
.
Juvenile sharptail molas are known to feed on benthic annelid
Annelid
The annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
s and sponges. Adults likely feed on medusa
Medusa (biology)
In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, in contrast with polyps. Medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below...
e, siphonophores, ctenophore
Ctenophore
The Ctenophora are a phylum of animals that live in marine waters worldwide. Their most distinctive feature is the "combs", groups of cilia that they use for swimming, and they are the largest animals that swim by means of cilia – adults of various species range from a few millimeters to in size...
s, and salp
Salp
A salp or salpa is a barrel-shaped, planktonic tunicate. It moves by contracting, thus pumping water through its gelatinous body...
s, as well as some 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...
es, 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, and molluscs. Sharptail molas sometimes have remora
Remora
The remora , sometimes called a suckerfish or sharksucker, is an elongated, brown fish in the order Perciformes and family Echeneidae...
s attached to the surface of their bodies or inside the buccal cavity. In 1949, a sharptail mola off North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
was found with a common remora (Remora remora) wedged inside the gill arches on its right side. This evidently impaired the respiration
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
of the mola, such that it foundered on the beach and was collected by fishermen.
Molas are oviparous and are amongst the most fecund of all fishes. Larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l sharptail molas are rounded in shape and develop large pyramidal dermal spines over the body, which persist through a prejuvenile phase called the "Molacanthus" stage. In this stage, the body is deep and compressed, with a thin keel-like structure below the abdominal region. This ridge is made from skin and covered with several rows of small spines. The skin is rough, being covered with small prickles. The spines eventually diminish in size and disappear, leaving scars obvious on the sides of young fish up to 70 mm (2.8 in) long. Their coloration is dark brown on the back, becoming very light on the sides and belly. The lifespan
Life expectancy
Life expectancy is the expected number of years of life remaining at a given age. It is denoted by ex, which means the average number of subsequent years of life for someone now aged x, according to a particular mortality experience...
for this species is estimated to be 85 years for males and 105 years for females.
Relationship to humans
Since 2002, promotion of an ocean sunfish festival in Hualien CountyHualien County
Hualien County is the largest county in Taiwan and is located on the mountainous eastern coast of Taiwan. It contains the island's largest port. It is the starting point of the Hualien-Taitung Line and the terminal point of North-Link Line of TRA...
, Taiwan has increased demand for the meat of the sunfish (called "mambo fish" after a public vote), whereas before only the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s and reproductive organs were sold while the rest of the fish was discarded. The month-long April festival draws some 120,000 visitors and features "101 ways to eat" sunfish. Consequently, catches of sunfishes off eastern Taiwan have risen sharply, with the sharptail mola comprising 90% of the catch. In 2005, 208 tonnes were landed and the annual sunfish catch was valued at one million USD. The species is caught by set net, drift net, and longline fisheries. The impact of this increased exploitation on sunfish stocks is under investigation.