Short-finned eel | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Order: | Anguilliformes |
Family: | Anguillidae |
Genus: | Anguilla |
Species: | A. australis |
Binomial name | |
Anguilla australis J. Richardson, 1841 | |
The short-finned eel (Anguilla australis), also known as the shortfin eel, 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.
The body of the adult short-finned eel is long and snakelike, roughly tubular and the head is small, with the jaws reaching back to below the eye or further. The dorsal (top) and anal (bottom) 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. [2]
Anguillid eels are undifferentiated gonochoristic fish. [3] 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 (30 cm (12 in)) of the animal, not its age. [4]
They are common throughout the lowlands of New Zealand, including both Chatham and Stewart Island/Rakiura, but tend not to ascend as far inland as New Zealand longfin eels. [5]
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 Dividing Range, and not extending as far west as the outlet of the Murray River, they are excluded from the thousands of kilometres of waterways that drain inland eastern Australia. [5]
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 Southern Equatorial Current region (14.5–21°S, 154–179.5°E). [5]
During their life cycle however, eels migrate over huge distances to spawn. [4]
They are carnivorous, and ferocious predators, eating crustaceans, fish, frogs, birds, [6] snakes, and Australian native water rats (rakali). [4]
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 Sea 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, whereas temperate species such as the short-finned eel have strong seasonal recruitment. [7] 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. [8]
The leptocephalus ("narrow head" larvae), drift on the ocean currents (off Australia, the South Equatorial Current and eventually reach coastal waters, where they metamorphose into "glass eels" (tiny, semi-transparent eels). At this stage they are unable to eat, and can only eat after reaching an estuary or river mouth, where they metamorphose again into elvers, which are darker in colour. From there, they migrate upstream, traversing numerous obstacles — if necessary, leaving the water and travelling short distances over moist ground. They are well-suited to this task, being able to absorb some of the oxygen they need through the skin. [4]
It is only when they reach about 30 cm (12 in) in length that they hit puberty and it is only then that their sex, which depends on population density, is determined. In an area with many eels, they tend to turn into males, whereas further upstream, where there are fewer eels, they are more likely to become female. [4] Eventually, they take up residence in a lake, swamp, dam or river, typically occupying a home range of about 400 m (1,300 ft) in length, where they remain until they reach maturity at about 14 years for males and 18 to 24 years for females.[ citation needed ]
At some point, the eels start changing their shape again, to prepare for a trip back into the ocean for spawning. Their digestive system shrinks and their gonads become larger, to make room for the eggs and sperm that they will be making, and they stop eating. Their eyes get bigger, and their heads pointier, possibly an adaptation for better ocean swimming. In the case of the south-east Australian eels, they head north up the east coast, heading for the Coral Sea. A 2021 study by the Arthur Rylah Institute tracked short-finned eels that travelled 2,620 km (1,630 mi) from western Victoria up the east coast to the Coral Sea. The study did not establish where the eels spawned, but the researchers thought that it was somewhere near New Caledonia. [4]
As of 2000 [update] , 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 pubertal stage, but much less is known about the marine stage [9] Research done in 2008 identified that tropical species such as A. reinhardtii (Australian long-finned eels [4] ) have a shorter larval migration and faster corresponding growth, suggesting a water temperature effect on growth. [5]
Like other anguillids, 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 introduction of European and American species.[ citation needed ]
Short-finned eels make excellent eating and have long been esteemed as an important food. The consumption of short-finned eels is a longstanding tradition in many Pacific nations, including Japan, Australia and New Zealand.
Prior to European settlement at least two Aboriginal Australian nations, 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. The short-finned eel is known to Māori as tuna, alongside the endemic New Zealand longfin eel. [11] They had a highly developed fishery for freshwater eels before the arrival of Europeans, and an extensive knowledge of the ecology of eels, harvesting them through a variety of techniques. Present-day recreational anglers catch and eat them regularly, and New Zealand has a well-established commercial eel fishery. Māori are now concerned that the commercial fishery is compromising their ability to harvest short-finned eels for ceremonial purposes. [2]
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. [8] The increasing pressure on eels has led to reduced recruitment of juveniles of anguilid species which limits the industry and potentially leads to ecological impacts. [9] 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.[ citation needed ]
Extensive systems of aquaculture to farm the short-finned eel were developed by the Gunditjmara people of western Victoria, Australia, dating to at least 7,000 years ago in the wetlands created by the Tyrendarra lava flow of the Budj Bim volcano. Today, the areas are protected by three Budj Bim heritage areas. [12] The eel was known as kooyang in the Gunditjmara language. [13] [14]
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. [3] 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. [15]
However the main way that full growth of oocytes is achieved is by repeated injections of salmon pituitary extracts, [15] and also additions of other hormones.
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.
Eel farming was trialled in New Zealand in the 1970s [2] 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 Research) has begun developing culture and husbandry techniques in freshwater, and will also be investigating trials in saltwater.
New Zealand is in a unique position where the shortfin eel stock, despite heavy exploitation, show little evidence of decline nationally. [2] 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. [16]
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.) [3]
Water temperature has a notable effect 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 [8] 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. [8] It has been shown in the European eel that they achieve higher growth when in saline. [5] Much research continues in this area.
A major problem in the sustainability of aquaculture of these eels is controlling reproduction and larval development. Culture conditions have a skewed male sex ratio from a small body size. This size difference between sexes is seen in eels housed within a tank. Males are smaller than females and some size difference extends 3g-270g. [8] Many fisheries therefore concentrate on females, except for the Lake Ellesmere (New Zealand) fishery which consists of a two-thirds male catch. [2] The goal of many aquaculture operations is to favour female development, the most common way is by the addition of hormones however this is not favoured in all areas of the world. [3]
The Budj Bim National Park, formerly known as Mount Eccles National Park, is a national park located in the Western District of Victoria, Australia. The 5,470-hectare (13,500-acre) national park is situated approximately 270 kilometres (170 mi) west of Melbourne and approximately 15 kilometres (9.3 mi) southwest of Macarthur. It derives its name from Budj Bim, formerly Mount Eccles, which is situated in the north-east of the park.
The European eel is a species of eel. They are critically endangered due to hydroelectric dams, overfishing by fisheries on coasts for human consumption and parasites.
The American eel is a facultative catadromous fish found on the eastern coast of North America. Freshwater eels are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender, supple, snake-like body that is covered with a mucus layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fins can be found near the midline, followed by the head and gill covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was long a mystery. Of particular interest has been the search for the spawning grounds for the various species of eels, and identifying the population impacts of different stages of the life cycle.
The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Except from the genus Neoanguilla, with the only known species Neoanguilla nepalensis from Nepal, all the extant species and six subspecies in this family are in the genus Anguilla, and are elongated fish of snake-like bodies, with long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous, spending their adult lives in freshwater, but migrating to the ocean to spawn.
The eel-tailed catfish, Tandanus tandanus, is a species of catfish of the family Plotosidae. This fish is also known as dewfish, freshwater catfish, jewfish, and tandan.
A fish trap is a trap used for catching fish and other aquatic animals of value. Fish traps include fishing weirs, cage traps, fish wheels and some fishing net rigs such as fyke nets.
The New Zealand longfin eel, also known as ōrea, is a species of freshwater eel that is endemic to New Zealand. It is the largest freshwater eel in New Zealand and the only endemic species – the other eels found in New Zealand are the native shortfin eel, also found in Australia, and the naturally introduced Australian longfin eel. Longfin eels are long-lived, migrating to the Pacific Ocean near Tonga to breed at the end of their lives. They are good climbers as juveniles and so are found in streams and lakes a long way inland. An important traditional food source for Māori, who name them ōrea, longfin eel numbers are declining and they are classified as endangered, but over one hundred tonnes are still commercially fished each year.
The speckled longfin eel, Australian long-finned eel or marbled eel is one of 15 species of eel in the family Anguillidae. It has a long snake-like cylindrical body with its dorsal, tail and anal fins joined to form one long fin. It usually has a brownish green or olive green back and sides with small darker spots or blotches all over its body. Its underside is paler. It has a small gill opening on each side of its wide head, with thick lips. It is Australia's largest freshwater eel, and the female usually grows much larger than the male. It is also known as the spotted eel.
The giant kōkopu is a threatened species of ray-finned fish in the genus Galaxias, found only in New Zealand. It can reach up to 58 cm (23 in) in length and 2.7 kg (6.0 lb) in weight, making it the largest species in the family Galaxiidae. It is a mainly lowland species, commonly found in slow-flowing streams, wetlands, lakes, and lagoons. Most populations have an amphidromous life cycle, with larvae going to sea soon after hatching and returning about four months later as small juveniles, 4.5–5 cm (1.8–2.0 in). Juvenile giant kōkopu form a small part of the annual whitebait catch.
Paracalliope is a genus of amphipod crustaceans that live in Australasia. They include the most common freshwater amphipods in New Zealand, where they are particularly frequent in slow-flowing reaches of rivers. They shelter among weed beds and are important prey items for fish such as the New Zealand smelt, Retropinna retropinna, which are in turn important prey for the freshwater eels Anguilla australis and Anguilla dieffenbachii. Paracalliope acts as an intermediate host for the nematode Hedruris spinigera, which can thus reach their primary host, the eel.
The Japanese eel is a species of anguillid eel found in Japan, Korea, Taiwan, China, and Vietnam, as well as the northern Philippines. Like all the eels of the genus Anguilla and the family Anguillidae, it is catadromous, meaning it spawns in the sea but lives parts of its life in freshwater. Raised in aquaculture ponds in most countries, the Japanese eel makes up 95% of the commercially sold eel in Japan, the other 5% is shipped over by air to the country from Europe. This food in Japan is called unagi; they are an essential part of the food culture, with many restaurants serving grilled eel called kabayaki. However, presumably due to a combination of overfishing and habitat loss or changing water conditions in the ocean interfering with spawning and the transport of their leptocephali this species is endangered.
The giant mottled eel, also known as the marbled eel, is a species of tropical anguillid eel that is found in the Indo-Pacific and adjacent freshwater habitats.
Eels are ray-finned fish belonging to the order Anguilliformes, which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.
Aquaculture in Australia is the country's fastest-growing primary industry, accounting for 34% of the total gross value of production of seafood. 10 species of fish are farmed in Australia, and production is dominated by southern bluefin tuna, Atlantic salmon and barramundi. Mud crabs have also been cultivated in Australia for many years, sometimes leading to over-exploitation. Traditionally, this aquaculture was limited to table oysters and pearls, but since the early 1970s, there has been significant research and commercial development of other forms of aquaculture, including finfish, crustaceans, and molluscs.
Telogaster opisthorchis is an endoparasite in the class Trematoda within the phylum Platyhelminthes. This fluke is known for causing tumor like malformations in fishes by attaching onto its spinal region in the metacercariae form. Malformations cause fish to become more susceptible to fish eating predators allowing T. opisthorchis to continue with its lifecycle.
The Pacific shortfinned eel, also known as the Pacific shortfinned freshwater eel, the short-finned eel, and the South Pacific eel, is an eel in the family Anguillidae. It was described by Albert Günther in 1871. It is a tropical, freshwater eel which is known from western New Guinea, Queensland, Australia, the Society Islands, and possibly South Africa. The eels spend most of their lives in freshwater, but migrate to the Pacific Ocean to breed. Males can reach a maximum total length of 110 centimetres, but more commonly reach a TL of around 60 cm. The Pacific shortfinned eel is most similar to Anguilla australis, and Anguilla bicolor, but can be distinguished by the number of vertebrae.
Fish go through various life stages between fertilization and adulthood. The life of fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.
Cyvirus anguillidallo1, also known as Anguillid herpesvirus 1 (AngHV-1) is a species of virus in the genus Cyprinivirus, family Alloherpesviridae, and order Herpesvirales.
Budj Bim heritage areas includes several protected areas in Victoria, Australia, the largest two being Budj Bim National Heritage Landscape and the Budj Bim Cultural Landscape. Within the latter, there are three Indigenous Protected Areas: the Tyrendarra Indigenous Protected Area, Kurtonitj Indigenous Protected Area, and the Lake Condah Indigenous Protected Area.