Effects of water temperature on early development of Japanese eel Anguilla japonica

To determine an optimal temperature range for efficient production of healthy eel larvae Anguilla japonica, the effect of water temperature on hatching, survival, and deformity rates was examined. The early ontogeny of morphological features in this species by incubating eggs at five different temperatures (19, 22, 25, 28 and 31 degrees C) was examined. Hatching occurred at 24, 28, 46 and 58 h after fertilization when incubated at 28, 25, 22 and 19 degrees C, respectively; no eggs hatched at 31 degrees C. The growth rate of prefeeding larvae increased as water temperature was elevated and acquisition of feeding ability was also accelerated at higher temperature. Significantly high hatching rates (76-86%, P < 0.05) and survival rates (61-86%, P < 0.05) were observed at relatively high temperatures (22-28 degrees C). The deformities were 'open lower jaw', 'pericardial edema', and 'notochordal bending', in which the mouth was deformed with a downward projecting lower jaw, the pericardial cavity was swollen, and the notochord was bent or twisted to various degrees, respectively. Open lower jaw and pericardial edema were especially predominant at 19 degrees C, with rates of 68 and 92%, respectively, compared with 31 and 10% at 25 and 28 degrees C, respectively. The occurrence of notochordal bending was not affected by temperature. The optimal temperature for incubation and rearing A. japonica eggs and prefeeding larvae is approximately 25-28 degrees C.