Techniques for Larval Rearing

Abstract

Techniques for artificial breeding of the Japanese eel, Anguilla japonica, have been studied intensively since the 1960s. Yamamoto and Yamauchi (1974) first succeeded in obtaining fertilized eggs and larvae of the Japanese eel by hormone treatment, and preleptocephalus larvae were reared for 2 weeks (Yamauchi et aL.1976). Thereafter, many researchers succeeded in obtaining eel larvae (Satoh 1979; Wang et al. 1980; Yu et al. 1993), but suitable larval feeds were not identified. As a result, preleptocephalus larvae could not survive beyond the depletion of their yolk and oil droplet stores. In other eel species, for example, the European eel A. anguilla (Prokhorchik 1986) and the New Zealand freshwater eels A. dieffenbachii and A. australis (Lokman and Young 2000), experimentally produced larvae survived only for a few days and, like the Japanese eel, did not develop into leptocephali. Thus, the transition from preleptocephalus, just before first feeding, into the willow leafshaped leptocephalus stage caught in the wild has never been observed. Therefore, attempts to rear captive-bred eel larvae in aquaria to observe this transition have been intensively continued, which is of obvious benefit for both clarifying the eel life history and artificial propagation programs. Tanaka et al. (2001) recently discovered that a slurry-type diet made from shark-egg powder is a suitable feed for captive-bred eel larvae. Larvae were reared on this diet for more than 200 days and raised to 31 mm in total length (TL).