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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 23°C were
able to adapt to temperatures of 18~28°C. However, the hatching rate
was significantly lower when morula and gastrula stages were
transferred to 18°C. The survival rate at the eye-pigmented stage was
highest at 26°C for all 3 embryonic stages. Moreover, C-shaped embryos
were able to tolerate a higher temperature (30°C) if acclimated to 26°C
prior to the trial. One-day-old yolk-sac larvae, on the other hand,
were able to adapt to temperatures of 3~32°C. The highest survival
rates at the eye-pigmented stage were observed at 26~30°C. From the
above results and considering other technicalities of spawning and
incubation, it is suggested that water temperatures be regulated in the
range of 24~26°C for incubation of Japanese eel embryos, and 26~28°C
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 (> 24°C) 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
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