FAMILY: Anguillidae
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NAME: Anguilla anguilla - European eel
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Data provided courtesy of Aquaculture/Fisheries Center, University of Arkansas at Pine Bluff - (Dr. Peter Perschbacher) |
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Fresh- and brackishwater systems of Europe and north of Africa. The European eel migrates from the sea to freshwater during its larval and juvenile stages. Adult eels return to the sea to breed. HABITS: Eels are found in marine coastal waters, brackish waters (estuaries, lagoons, mangroves), and inland waters (rivers, streams, lakes, and marshes). For most of their lives (3 to 12-15 years) they are mainly sedentary, but they undertake significant marine migrations during the course of their complex biological cycle. SPAWNING: The spawning ground of the European eels partly overlaps that of the American eel and is found in the West Atlantic, in the Sargasso Sea (22-29° N, 50-70° W). Spawning has not yet been observed because of the difficulty of catching eels in the sea. It takes place at 600 m depth in darkness and under high pressures between March and July, as has been demonstrated by the appearance of eggs in plankton samples. GROWTH: After the eggs have hatched, the leptocephalus larvae (more than 7 mm long) drift northeast on the Gulf Stream. Their growth from 10 to 45 mm, and up to 75 mm, indicates the time taken for migration. The time taken for the journey is nor well known but has been estimated at several years (3-5). When the leptocephalus larva arrives on the European or African continental shelf a marked anatomical and physiological change takes place during which the leptocephalus turns into a transparent elver. It becomes cylindrical and undergoes endocrine changes. The elvers, which have developed the ability to osmoregulate, are attracted by freshwater running off the land. During the ascent of rivers and streams the transparent elvers become pigmented. The state of distribution of the melanophores allows the distinction of several precise stages. Once in brackish lagoons or in freshwater the young eels, which are yellowish to greenish brown become increasingly sedentary and territorial, adopting a large solitary existence, marked by a high rate of feeding on a wide range of animal species. Their diet is composed of copepod, amphipod, isopod, and decapod crustaceans, insect larvae, polychaetes, gastropods, and small fish. Growth is therefore rapid during the warm season, May-October, but during cold periods in the autumn, winter, and spring, when water is below 10-12° C, feeding and growth cease. After a stay of 5-15 years in inland waters the yellow eels undergo major changes which can be identified as metamorphosis. Their skin becomes darker on the back and silvery on the ventral surface, among other changes. Silver eels leave fresh water during the autumn and begin an extremely long migration through rivers and estuaries to the sea. During this migration they become sexually mature and are ready to spawn in spring or summer. It is not known whether they survive spawning. USES: An unusual feature of the eel is that it is exploited at almost all stages of development, excepting the leptocephalus stage. There are fisheries for elvers, yellow eels, and silver eels; the eel is thus of great economic importance. However, natural populations are declining due to increased pollution of rivers. On the other hand, imports are not adequate to satisfy the high demand for eels, which exists in virtually every European country. Thus, it is easily understood why interest in the culture of the native Anguilla anguilla is growing not only in Europe but in Israel and the United Arab Republic as well. CULTURE: The eel is an undomesticated species in that it has not yet been possible to produce young in a hatchery (artificial fertilization is possible, but larval mortality follows soon after hatching). Thus, culture operations are entirely dependent on catches of wild eels. Supplies are extremely variable in quantity and in quality. Their genetic make-up is unknown, so selection is impossible. Any reduction in stocks available for exploitation can have serious effects on the progress of culture. Strict health measures are imposed to prevent the introduction of pathogens and parasites. The classic rearing stages include: 1) a nursery stage where the elvers and young eels are conditioned to a particular type of diet (natural, artificial, or mixed); and 2) an on-growing stage for the 20-30% of individuals which are suitable for culture and are selected by successive grading. They are fed on artificial diets and will reach 200-250 g, market size, in 18-24 months. Overall, growth of eels in culture is generally significantly faster than that in the wild because of the improved nutritional and temperature conditions. REFERENCES:
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