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

Abstract

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 25°C, respectively. Thus the egg-laying rate increases progressively with temperature from 10 to 20°C, but no significant difference was detected between values at 20 and 25°C or between 15 and 25°C. While all the eggs obtained below 20°C appeared normal with straight appendages at both ends, 1.4% of the eggs obtained at 25°C appeared abnormal, suggesting that 25°C is at or near the upper limit for the normal egg-laying of this parasite.