Salinity adaptation and subsidence attributes in the early stages of Japanese eel (Anguilla japonica)

Abstract

The tolerance of Japanese eel (Anguilla japonica) embryos to abrupt changes in salinity and their effect on subsidence and survival of yolk-sac larvae were investigated. Results show that the survival of normal and eye-pigmented larvae were significantly higher after transferring the embryos from 30 ppt to 25 and 30 ppt compared to the other salinity treatments tested. C- shaped embryos showed stronger ability to overcome changes in salinities than did morula embryos. The subsidence of yolk-sac larvae was positively correlated with age and the decrease in salinity. Most larvae in 30-ppt water moved to the lower water layer or lay on the bottom from 2 days old, while in the 20-ppt group, almost all larvae from 1 day old sank to the lower layer or lay on the bottom. The survival rate of eye-pigmented larvae was significantly higher at 30 ppt compared to other salinity levels in the experimental trial on larval subsidence. Moreover, decreases in survival of yolk-sac larvae were significantly affected by the presence of copepods and the bottom substrate (sand and silt).