Effects of Water Temperature on the Development of the Monogenean Neoheterobothrium hirame on Japanese Flounder Paralichthys olivaceus

Abstract

Development and growth of the monogenean Neoheterobothrium hirame on Japanese flounder Paralichthys olivaceus were investigated at 15°C, 20°C and 25°C, and production of antibodies against N. hirame was monitored in relation to the development of the parasite. After settlement on the gill filaments, hematin cells in the gut wall of N. hirame were first observed on Day 17, Day 10 and Day 7 post-exposure (PE) of oncomiracidia at 15°C, 20°C and 25°C, respectively. The parasite started to move to the buccal cavity wall from Day 38, Day 24 and Day 24 PE and eggs were observed in the uterus from Day 59, Day 38 and Day 31 PE at each temperature, respectively. Intensity of infection decreased subsequently and infection persisted until Day 122, Day 66 and Day 52 PE, respectively. Antibody titers gradually increased from Day 52 PE at 15°C, while at 20°C and at 25°C, they rapidly increased after a decrease in the intensity and prevalence of the infections was observed. This suggests that the death of the parasite induces a host reaction, resulting in the production of antibodies against N. hirame.