Zoological Studies

Vol. 43 No. 3, 2004

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

Su-Lean Chang1,2, Guang-Hsiung Kou2 and I Chiu Liao3,*

1Tungkang Marine Laboratory, Taiwan Fisheries Research Institute, Pingtung, Taiwan 928
2Department of Zoology, National Taiwan University, Taipei, Taiwan 106
3National Taiwan Ocean University, Keelung, Taiwan 202

Su-Lean Chang, Guang-Hsiung Kou and I Chiu Liao (2004) The biology and ecology of Japanese eel (Anguilla japonica) in the early developmental stages are still not clear. This study was conducted 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 23C were able to adapt to temperatures of 18~28C. However, the hatching rate was significantly lower when morula and gastrula stages were transferred to 18C. The survival rate at the eye-pigmented stage was highest at 26C for all 3 embryonic stages. Moreover, C-shaped embryos were able to tolerate a higher temperature (30C) if acclimated to 26C prior to the trial. One-day-old yolk-sac larvae, on the other hand, were able to adapt to temperatures of 3~32C. The highest survival rates at the eye-pigmented stage were observed at 26~30C. From the above results and considering other technicalities of spawning and incubation, it is suggested that water temperatures be regulated in the range of 24~26C for incubation of Japanese eel embryos, and 26~28C for incubation of yolk-sac larvae. Based on temperature adaptation and good buoyancy of eel embryos, we speculated that eel eggs may float up to the warm water layer of the sea (> 24C) which is above the putative spawning 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 phototactic behavior during the eye-pigmented stage.

Key words: Anguilla japonica, Embryo, Yolk-sac larvae, Water temperature.

*Correspondence: Tel: 886-2-24623055. Fax: 886-2-24634994. E-mail: icliao@mail.ntou.edu.tw