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 degrees C. Hatching time was shortened at higher temperatures with eggs at 28 degrees C hatching within 23-28 h after fertilization, while eggs at 19 degrees C took 48-54 h for their hatching. At 22 and 25 degrees C, eggs hatched out within 35-43 h and 27-32 h, respectively. There was no successful hatching at 16 or 31 degrees 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 degrees C differed among the lots. Eggs maintained at 25 degrees C showed a high hatching rate (mean: 69%), compared to other water temperatures (mean: 12% at 19 degrees C, 32% at 22 degrees C, 4% at 28 degrees C). The results from present study indicate that the optimal temperature for egg incubation is around 25 degrees C. similar to the likely temperatures experienced by eggs and early larvae in the spawning area. (C) 2011 Elsevier B.V. All rights reserved.