Experimental study on the ecology of Cichlidogyrus sclerosus（Monogenea）on Tilapia

The experimental study on the ecology of Cichlidogyrus sclerosus (Papema & Thurston, 1969) was carried out, including the effect of temperature on egg production, egg hatching, larval infection, size and life-sapn of adult parasite, and the susceptibilities of three different strains/species of tilapia, namely O. niloticus, O. aureus and the hybrid of them, by C. sclerosus.

Egg production and hatching speed were positively correlated with temperature when under 30℃, and the peak occurs at 30℃. Eggs hardly hatched at 35℃. Infection of oncomiracidia peaked at 25℃ with a prevalence of 78.95%, while the prevalences at 20℃ and 30℃ were 58.94% and 21.02%  respectively. The abundance and mean intensity of C. sclerosus on the gills of O. niloticus were positively correlated with temperature under 30℃, and reached a peak at 30℃. At 35℃, no parasite was found.

The life span and generation time were negatively correlated with temperature. They were 80 days and 11 days, 60 days and 5 days, 30 days and 4 days, at 20℃, 25℃, 30℃ respectively. When temperature reached 35℃，the parasites died soon. The infection of C. sclerosus on O. niloticus peaked after 6 weeks, while it peaked after 5 weeks on the other two species/strain of tilapias, O. aureus and the hybrid of O. niloticus and O. aureus, but there was no significant difference among the 3 peak values.

Key Words: Tilapia, Cichlidogyrus sclerosus, Experimental study on ecology.