Temperature Adaptation of the Japanese Eel (Anguilla japonica) in its Early Stages

Abstract

(Anguilla japonica) in its early stages. Zoological Studies 43(3): 571-579. The biology and ecology of Japanese eel (Anguilla japonica) in the early developmental stages are still not clear. This study was conduct-ed to determine the optimum water temperature for incubation of embryos and yolk-sac larvae of this eel. Results show that both embryos and yolk-sac larvae are able to adapt to wide ranges of water temperatures. The embryos at the morula, gastrula, and C-shaped stages initially incubated at 23°C were able to adapt totemperatures of 18~28°C. However, the hatching rate was significantly lower when morula and gastrulastages were transferred to 18°C. The survival rate at the eye-pigmented stage was highest at 26°C for all 3embryonic stages. Moreover, C-shaped embryos were able to tolerate a higher temperature (30°C) if acclimat-ed to 26°C prior to the trial. One-day-old yolk-sac larvae, on the other hand, were able to adapt to tempera-tures of 3~32°C. The highest survival rates at the eye-pigmented stage were observed at 26~30°C. From theabove results and considering other technicalities of spawning and incubation, it is suggested that water tem-peratures be regulated in the range of 24~26°C for incubation of Japanese eel embryos, and 26~28°C forincubation of yolk-sac larvae. Based on temperature adaptation and good buoyancy of eel embryos, we specu-lated that eel eggs may float up to the warm water layer of the sea (> 24°C) which is above the putative spawn-ing water layer (100 m in depth). On the other hand, hatched yolk-sac larvae may sink to the colder water layer and dim environment based on their tolerance of low temperatures, subsidence attributes, and negative photo-