Abstract:
Juvenile stages of Catla catla collected from Udawalawa Fish Breeding Station of the National Aquaculture Development Authority of Sri Lanka were found to be infested mainly with Gyrodactylus sp., digenean metacercarial cysts and Lernaea cyprinacea. In the present study, the intensities of parasite infections, preference sites of the parasites on fish, oxygen consumption rate and histological structure of the infested sites of the host fish were examined in comparison to the control fish to evaluate the effects of parasitic infestation on the host fish. Gyrodactylus sp. and digenean metacercarial cysts were recovered from the gills, whereas adult females of L. cyprinacea were found attached to the skin and fins of the fish. The intensities of Gyrodactylus sp. and the metacercarial cysts were 1-2368 individuals and 1-80 cysts per infected fish respectively. The intensity of L. cyprinacea ranged from 1 to 5 individuals per infected fish. Gyrodactylus sp. and metacercarlal cysts had no specific preference sites on the gills whereas caudal peduncle region of the fish was preferred by L. cyprinacea. Histopathological study revealed that infection of fish with Gyrodactylus, and digenean metacercarial cysts had induced moderate hyperplasia of the infected gill lamellae and deformation of part of some gill filaments of the host fish. Attachment of L. cyprinacea had triggered inflammatory tissue reaction at the infested site of the fish. In spite of these histopathological changes induced by the parasites on the infected sites, the oxygen consumption rates of the fish were not affected significantly by the presence of parasites at the current infestation level
