Effects of water temperature on the egg-laying of the monogenean Neoheterobothrium hirame

摘要

The egg-laying rates of the monogenean Neoheterobothrium hirame, a parasite of Japanese flounder, were measured at different water temperatures. The daily egg-laying rates per worm were 203, 578, 781 and 651 eggs at 10, 15, 20 and 25degreesC, respectively. Thus the egg-laying rate increases progressively with temperature from 10 to 20degreesC, but no significant difference was detected between values at 20 and 25degreesC or between 15 and 25degreesC. While all the eggs obtained below 20degreesC appeared normal with straight appendages at both ends, 1.4% of the eggs obtained at 25degreesC appeared abnormal, suggesting that 25degreesC is at or near the upper limit for the normal egg-laying of this parasite.