MIGRATION OF DIPLOSTOMUM NIEDASHUI CERCARIAE IN THE RARE MINNOW GOBIOCYPRIS RARUS WITH OBSERVATION ON THE PARASITE-INDUCED OTOLITH CHECKS

The penetration and migration of the eyefluke Diplostomum niedashui,a common parasite of freshwater fish in China were investigated using the rare minnow Gobiocypris rarus as the second intermediate host. The first intermediate host,Lymnaea stagnalis was collected from a fish farm in Wuhan,Hubei province of China,and the snails shedding cercariae were maintained in the laboratory. The cercariae of D. niedashui were identified according to the original description,and used to infect the rare minnow. Infected fish were either fixed in Bouin's solution and then sectioned before being stained in H-E,or observed live under microscope. Otoliths of some infected fish were dissected out for the examination of checks. The penetration of cercariae was observed on the whole body surface of the fish,while most cercariae were found on the head region of the fish, suggesting that the head region is the main site for the penetration. Although the penetrated cercariae were observed in the notochord,no meta-cercariae were found in the optic nerve,nor to migrate to the brain and to the eye through the nervous system. The metacercariae were found frequently in muscles and connective tissues of the fish and found moving directly into the lens through the muscle and connective tissue of the fish. The examination of otolith microstructure revealed some differences between the infected and un-infected fish,and checks on the otolith were found when the infection occurred,indicating that the parasite infection may induce the formation of checks on otoliths.