Short-finned eel
Encyclopedia
The short-finned eel, Anguilla australis, is one of the 15 species
of eel
in the family Anguillidae
. It is native to the lakes, dams and coastal rivers of south-eastern Australia
, New Zealand
, and much of the South Pacific
, including New Caledonia
, Norfolk Island
, Lord Howe Island
, Tahiti
, and Fiji
.
, but tend not to ascend as far inland as long-finned eel
s. In Australia, they are restricted to the area on the seaward side of the Great Dividing Range
, from about Mount Gambier
in the south-eastern corner of South Australia
, through Victoria, Tasmania, the Bass Strait islands and up the eastern seaboard to the Richmond River
in northern New South Wales
. Unable to scale the Great Divide, and not extending as far west as the outlet of the Murray River
, they are excluded from the thousands of miles of waterways that drain inland eastern Australia. A. Australis is the most widely distributed longitudinally of the Anguillid eels where its larvae can be found just south of Fiji to the North-west of Australia in the SEC region (14.5-21°S, 154-179.5°E) (For a comparison with northern hemisphere eels, in particular the European eel
, see eel life history
.) The larvae
drift on the ocean current
s and eventually reach coastal waters, where they metamorphose into elvers (tiny, semi-transparent eels). From there, they migrate upstream, traversing numerous obstacles — if necessary, leaving the water and travelling short distances over moist ground. They are well fitted to this task, being able to absorb 50% of the oxygen they need through the skin. Eventually, they take up residence in a lake, swamp, dam or river, typically occupying a home range of about 400 m in length, where they remain until they reach maturity at about 14 years for males and 18 to 24 years for females. They are carnivorous, eating crustacean
s, fish, frogs and even small birds.
off New Caledonia
. The larvae recruit from the sea as small adults when they lack colour and are transparent-giving them the name 'glass eel'. Tropical species have year round recruitment where temperate species such as the short-finned eel have strong seasonal recruitment. Recent evidence that has utilised analytical microchemical techniques in eel otoliths has suggested that eels are facultatively catadromous rather than obligatory. Discrete populations of ocean and estuarine residents exist, that very rarely enter freshwater.
Like other angullids, short-finned eels are remarkably hardy: they can tolerate high water temperatures and low oxygen concentrations, endure long periods without food, and bury themselves in mud or sand and enter an energy-saving torpor when the water temperature drops below 10°C
. They are one of the few Australian freshwater fish to have coped well with the wholesale introduction of European and American species.
at least two Aboriginal Australian civilisations, the Gunditjmara
and the Djab Wurrung
from Western Victoria, farmed eels on a large scale, trading smoked eel with distant communities in return for other goods. For the Māori people of New Zealand, starved of protein after the extinction of New Zealand megafauna
, the short-finned eel was a significant food resource. Present-day recreational anglers catch and eat them regularly, and New Zealand has a well-established commercial eel fishery.
) has begun developing culture and husbandry techniques in freshwater, and will also be investigating trials in saltwater.
Techniques for artificial breeding of the Japanese eel 'A. japonica' have been studied intensively since the 1960s. It is difficult to rear these animals in captivity, the main problem being incomplete techniques for inducing sexual maturation and incomplete rearing techniques of larvae.
However the main way that full growth of oocytes is achieved is by repeated injections of salmon pituitary extracts, and also additions of other hormones.
New Zealand is in a unique position where the shortfin eel stock, despite heavy exploitation, show little evidence of decline nationally. New Zealand is therefore in a position to enhance global production of shortfin eels and relieve pressure on other stocks around the world in countries such as China, Japan, Korea and Taiwan where aquaculture potential has been limited.
Most eel culture facilities utilise freshwater. However a saltwater eel farm operated in Bristol in the United Kingdom for 15 years, using warm seawater growing eels to a marketable size in 18–24 months (it was shut down for economic reasons.)
Water temperature has a notable affect on the metabolic activity of fish species. Anguillids can withstand a wide variety of temperatures but the optimum temperature in cultured species is between 22°C and 28°C- at this temperature growth is maximised Recent work has determined that the optimal water temperature is for maximal growth of short-finned eels is 26.5°C, and salinity is optimum at 17.5%. These parameters were shown to give the highest mean specific growth rate of these eels. It has been shown in the European eel that they achieve higher growth when in saline. Much research continues in this area.
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 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...
in the family Anguillidae
Anguillidae
Anguillidae is a family of fishes that contains the freshwater eels. There are 19 species/subspecies in this family, all in genus Anguilla. They are catadromous, meaning they spend their lives in freshwater rivers, lakes, or estuaries and return to the ocean to spawn...
. It is native to the lakes, dams and coastal rivers of south-eastern 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...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and much of the South Pacific
Oceania
Oceania is a region centered on the islands of the tropical Pacific Ocean. Conceptions of what constitutes Oceania range from the coral atolls and volcanic islands of the South Pacific to the entire insular region between Asia and the Americas, including Australasia and the Malay Archipelago...
, including New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
, Norfolk Island
Norfolk Island
Norfolk Island is a small island in the Pacific Ocean located between Australia, New Zealand and New Caledonia. The island is part of the Commonwealth of Australia, but it enjoys a large degree of self-governance...
, Lord Howe Island
Lord Howe Island
Lord Howe Island is an irregularly crescent-shaped volcanic remnant in the Tasman Sea between Australia and New Zealand, directly east of mainland Port Macquarie, and about from Norfolk Island. The island is about 11 km long and between 2.8 km and 0.6 km wide with an area of...
, Tahiti
Tahiti
Tahiti is the largest island in the Windward group of French Polynesia, located in the archipelago of the Society Islands in the southern Pacific Ocean. It is the economic, cultural and political centre of French Polynesia. The island was formed from volcanic activity and is high and mountainous...
, and Fiji
Fiji
Fiji , officially the Republic of Fiji , is an island nation in Melanesia in the South Pacific Ocean about northeast of New Zealand's North Island...
.
Morphology and growth
The body is long and snakelike, roughly tubular and the head is small, with the jaws reaching back to below the eye or further. The dorsal and anal fins are of roughly equal length. The colour varies considerably from one individual to another; a deep olive-green is typical but it can be much lighter; golden or even (rarely) yellowish. There are no markings of note, but the underside is pale, often silvery, and the fins greenish. When full grown, they reach about 90 cm. The short-finned eel has a typical regeneration time of 15 to 30 years for females and it reaches a maximum size of about 1.1 m and 3 kg. Males tend to be slower growing and reach a smaller adult size. Anguillid eels are undifferentiated gonochoristic fish. This means that the sex of the animal is determined from an undifferentiated gonad. Differentiation then occurs and an eel becomes male or female, and this is generally correlated to the size (20.0-22.5 cm) of the animal not its age.Distribution
They are common throughout the lowlands of New Zealand, including both Chatham and Stewart Island/RakiuraStewart Island/Rakiura
Stewart Island/Rakiura is the third-largest island of New Zealand. It lies south of the South Island, across Foveaux Strait. Its permanent population is slightly over 400 people, most of whom live in the settlement of Oban.- History and naming :...
, but tend not to ascend as far inland as long-finned eel
New Zealand longfin eel
The New Zealand Longfin eel is one of three freshwater eels found in New Zealand. The other two species of eel are the Shortfin eel which is also found in south-eastern Australia and the recently arrived Australian Longfin eel .The easiest method for identification of the New Zealand Longfin eel...
s. In Australia, they are restricted to the area on the seaward side of the Great Dividing Range
Great Dividing Range
The Great Dividing Range, or the Eastern Highlands, is Australia's most substantial mountain range and the third longest in the world. The range stretches more than 3,500 km from Dauan Island off the northeastern tip of Queensland, running the entire length of the eastern coastline through...
, from about Mount Gambier
Mount Gambier, South Australia
Mount Gambier is the largest regional city in South Australia located approximately 450 kilometres south of the capital Adelaide and just 17 kilometres from the Victorian border....
in the south-eastern corner of South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
, through Victoria, Tasmania, the Bass Strait islands and up the eastern seaboard to the Richmond River
Richmond River
The Richmond River is a river in the north-eastern corner of New South Wales, Australia. It runs for approximately 170 km from the foothills of the Border Ranges past the towns of Kyogle, Casino, Coraki, Woodburn, where it turns northward and empties into the Pacific Ocean at Ballina. It has a...
in northern New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
. Unable to scale the Great Divide, and not extending as far west as the outlet of the Murray River
Murray River
The Murray River is Australia's longest river. At in length, the Murray rises in the Australian Alps, draining the western side of Australia's highest mountains and, for most of its length, meanders across Australia's inland plains, forming the border between New South Wales and Victoria as it...
, they are excluded from the thousands of miles of waterways that drain inland eastern Australia. A. Australis is the most widely distributed longitudinally of the Anguillid eels where its larvae can be found just south of Fiji to the North-west of Australia in the SEC region (14.5-21°S, 154-179.5°E) (For a comparison with northern hemisphere eels, in particular the European eel
European eel
The European eel, Anguilla anguilla, is a species of eel, a snake-like, catadromous fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m....
, see eel life history
Eel life history
The eel is a long, thin bony fish of the order Anguilliformes. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was a mystery for a very long period of scientific history...
.) The larvae
Leptocephalus
A leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the Superorder Elopomorpha. Fishes with a leptocephalus larva stage include the most familiar eels such as the conger, moray eel, and garden eel, and the freshwater eels of the family Anguillidae, plus...
drift on the ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s and eventually reach coastal waters, where they metamorphose into elvers (tiny, semi-transparent eels). From there, they migrate upstream, traversing numerous obstacles — if necessary, leaving the water and travelling short distances over moist ground. They are well fitted to this task, being able to absorb 50% of the oxygen they need through the skin. Eventually, they take up residence in a lake, swamp, dam or river, typically occupying a home range of about 400 m in length, where they remain until they reach maturity at about 14 years for males and 18 to 24 years for females. They are carnivorous, eating 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, fish, frogs and even small birds.
Life History
Like the other anguillids, short-finned eels are catadromous: when they reach maturity, they stop feeding and migrate downstream to the sea, then anything up to three or four thousand kilometres to a spawning ground in deep water somewhere in the Coral SeaCoral Sea
The Coral Sea is a marginal sea off the northeast coast of Australia. It is bounded in the west by the east coast of Queensland, thereby including the Great Barrier Reef, in the east by Vanuatu and by New Caledonia, and in the north approximately by the southern extremity of the Solomon Islands...
off New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
. The larvae recruit from the sea as small adults when they lack colour and are transparent-giving them the name 'glass eel'. Tropical species have year round recruitment where temperate species such as the short-finned eel have strong seasonal recruitment. Recent evidence that has utilised analytical microchemical techniques in eel otoliths has suggested that eels are facultatively catadromous rather than obligatory. Discrete populations of ocean and estuarine residents exist, that very rarely enter freshwater.
Reproductive Biology
The reproductive biology of these eels has remained elusive during the marine phase. Much is known about the longer freshwater phase from the juvenile to puberal stage, but much less is known about the marine stage Newer research has identified that tropical species such as A. reinhardtii have a shorter larval migration and faster correspnding growth, suggesting a water temperature effect on growth.Like other angullids, short-finned eels are remarkably hardy: they can tolerate high water temperatures and low oxygen concentrations, endure long periods without food, and bury themselves in mud or sand and enter an energy-saving torpor when the water temperature drops below 10°C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
. They are one of the few Australian freshwater fish to have coped well with the wholesale introduction of European and American species.
Historical Background of the shortfinned eel
The consumption of short-finned eels is a longstanding tradition in many pacific nations. New Zealand’s indigenous Maori people had a highly developed fishery for freshwater eels before the arrival of Europeans. Maori people had an extensive knowledge of the ecology of eels and harvested them through a variety of techniques. Maori are now concerned that the commercial fishery is compromising their ability to harvest short-finned eels for ceremonial purposes. Prior to European settlement at least two Aboriginal Australian civilisations, the Gunditjmara and the Djab Wurrung from Western Victoria, farmed eels on a large scale, trading smoked eel with distant communities in return for other goods. For the Māori people of New Zealand, starved of protein after the extinction of New Zealand megafauna, the short-finned eel was a significant food resource. Present-day recreational anglers catch and eat them regularly, and New Zealand has a well-established commercial eel fishery.Food
Short-finned eels make excellent eating and has long been esteemed as an important food in the world. Eel or unagi is popular eating in Japan. Glazed eel or unagi-no-kabayaki is grilled and steamed where unadon includes uniagi. Prior to European settlementHistory of Australia
The History of Australia refers to the history of the area and people of Commonwealth of Australia and its preceding Indigenous and colonial societies. Aboriginal Australians are believed to have first arrived on the Australian mainland by boat from the Indonesian archipelago between 40,000 to...
at least two Aboriginal Australian civilisations, the Gunditjmara
Gunditjmara
Gunditjmara, or Gundidj for short, are an Indigenous Australian group from western Victoria . Their neighbours to the west were the Buandig people, to the north the Jardwadjali and Djab wurrung peoples, and in the east the Girai wurrung people.The name may also be spelt Gournditch-Mara...
and the Djab Wurrung
Djab Wurrung
The Djab wurrung people are Indigenous Australians who occupy the volcanic plains of central Victoria from the Mount William Range of Gariwerd in the west to the Pyrenees range in the east encompassing the Wimmera River flowing north and the headwaters of the Hopkins River flowing south. The towns...
from Western Victoria, farmed eels on a large scale, trading smoked eel with distant communities in return for other goods. For the Māori people of New Zealand, starved of protein after the extinction of New Zealand megafauna
Megafauna
In terrestrial zoology, megafauna are "giant", "very large" or "large" animals. The most common thresholds used are or...
, the short-finned eel was a significant food resource. Present-day recreational anglers catch and eat them regularly, and New Zealand has a well-established commercial eel fishery.
Eel Farming
Eel farming was trialled in New Zealand in the 1970s but had limited success. However, the implementation of new technology has made farming a viable option once more, with greater production efficiency. NIWA (National Institute of Water and Atmospheric ResearchNational Institute of Water and Atmospheric Research
The National Institute of Water and Atmospheric Research or NIWA , is a Crown Research Institute of New Zealand. Established in 1992, NIWA conducts commercial and non-commercial research across a broad range of disciplines in the environmental sciences...
) has begun developing culture and husbandry techniques in freshwater, and will also be investigating trials in saltwater.
Decline of wild seed
The main reason that the aquaculture of Anguillid eels has become more popular in recent times is that the wild seed supply cannot support the demand of the consumer. Because of declining catches of both the European and Japanese glass eels, seed from the short-finned eels is at a commercial premium. The increasing pressure on eels has led to reduced recruitment of juveniles of angullid species which limits the industry and potentially leads to ecological impacts. Supply of seed to aquaculture operations of these eels relies solely on wild stocks of glass eels. These stocks are declining and there is now pressure being placed on the development of intensive eel culture technology. Anguillid eels cannot be reared from eggs in a culture setting, it is the glass eels caught from wild stock that are reared.Aquaculture of the short-finned eel
Since short-finned eels make excellent eating, there is global demand for them. The major market is Japan with smaller markets in other parts of Asia and in Europe. Aquaculture is the single fastest growing animal food producing sector in the world, having an annual growth rate of 6.9%. The worldwide production of Anguillid eels from aquaculture is estimated to be 242 000 t per annum with a value of $US 1 billion. Chinese eel aquaculture production has increased dramatically over the last 10 years, now accounting for 75% of the total annual world production, and relies on the demand of the Japanese market.Techniques for artificial breeding of the Japanese eel 'A. japonica' have been studied intensively since the 1960s. It is difficult to rear these animals in captivity, the main problem being incomplete techniques for inducing sexual maturation and incomplete rearing techniques of larvae.
However the main way that full growth of oocytes is achieved is by repeated injections of salmon pituitary extracts, and also additions of other hormones.
Development of the industry
The important factors for developing and growing this industry are having viable and reliable seed sources, as well as understanding the basic biology of the animal. This includes an understanding of the times at which spawning in freshwater occurs as well as maintaining a sustainable catch of any given population.New Zealand is in a unique position where the shortfin eel stock, despite heavy exploitation, show little evidence of decline nationally. New Zealand is therefore in a position to enhance global production of shortfin eels and relieve pressure on other stocks around the world in countries such as China, Japan, Korea and Taiwan where aquaculture potential has been limited.
Most eel culture facilities utilise freshwater. However a saltwater eel farm operated in Bristol in the United Kingdom for 15 years, using warm seawater growing eels to a marketable size in 18–24 months (it was shut down for economic reasons.)
Water temperature has a notable affect on the metabolic activity of fish species. Anguillids can withstand a wide variety of temperatures but the optimum temperature in cultured species is between 22°C and 28°C- at this temperature growth is maximised Recent work has determined that the optimal water temperature is for maximal growth of short-finned eels is 26.5°C, and salinity is optimum at 17.5%. These parameters were shown to give the highest mean specific growth rate of these eels. It has been shown in the European eel that they achieve higher growth when in saline. Much research continues in this area.