Efficacy of high water temperature treatment against Pseudodactylogyrus spp. Infection in Japanese eel

Abstract

We investigated seasonal changes in the abundance of Pseudodactylogyrus spp. (Pd) in Japanese eel Anguilla japonica in culture ponds. For this purpose, the number of parasite eggs floating in the rearing water was counted as an indicator. In spring, the average number of floating eggs was 40.3 (SD=53.2) per liter of rearing water, which was maintained at 28-30°C by heating. In summer, the water temperature increased up to 30°C or higher without heating. During this period, the number of floating eggs was high at 30°C and was low at ≥ 32°C. The number of floating eggs was the highest (maximum number of eggs, 1,678 per liter) in autumn when the temperature ranged from 23°C to 30°C. In winter, the number of eggs was again low. On the basis of these results, we reared eels infected with Pd in fresh water at 29°C, 32°C and 35°C for 20 days to control this parasitic disease. Parasites did not decrease in number at 29°C, but clearly decreased at 32°C, and almost disappeared at 35°C within 5 days. When heavily infected eels were maintained at 35°C for 5 days in a greenhouse pond, mortality due to the infection clearly decreased. © 2009 The Japanese Society of Fish Pathology.