Effect of water temperature on embryonic development and hatching time of the Japanese eel Anguilla japonica

To obtain information about how water temperature affects the embryonic development of Japanese eel (Anguilla japonica) eggs, the developmental rates and hatching times of three lots of eggs were quantified at 16, 19, 22, 25, 28 and 31 °C. Hatching time was shortened at higher temperatures with eggs at 28 °C hatching within 23–28 h after fertilization, while eggs at 19 °C took 48–54 h for their hatching. At 22 and 25 °C, eggs hatched out within 35–43 h and 27–32 h, respectively. There was no successful hatching at 16 or 31 °C. The developmental stages until hatching were divided into morula, blastula, gastrula, eye vesicle and ear vesicle formation and heart formation. Development of the embryos were also faster at higher temperature especially after the gastrula stage, but the morphological features of each stage were the same at all water temperatures. The final developmental stage before the eggs died at 16 and 31 °C differed among the lots. Eggs maintained at 25 °C showed a high hatching rate (mean: 69%), compared to other water temperatures (mean: 12% at 19 °C, 32% at 22 °C, 4% at 28 °C). The results from present study indicate that the optimal temperature for egg incubation is around 25 °C, similar to the likely temperatures experienced by eggs and early larvae in the spawning area.

► The effect of water temperature on the embryo of the Japanese eel was investigated. ► Embryos developed faster at higher temperature. ► Embryos showed the highest hatching rate at 25 °C. ► Eggs failed to hatch at 16 °C and 31 °C. ► Water temperature strongly affects the embryos on their development and hatching.