Evaluation of the effects of infestation by trematodes and copepods on Catla catla, an Indian carp, cultured in Sri Lanka

Abstract

Juvenile stages of Catla catla collected from Udawalawa fisheries station, National Aquaculture Development Authority were found to be infested mainly with Gyrodactylus, digenean metacercarial cysts and Lernaea. In the present study, the intensity of infestation of the parasites and preference sites of the parasites on fish, the oxygen consumption rate, blood haematocrit levels 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(s) on the host fish. All trematodes were recovered from the gills, whereas Lernaea (a copepod) were found attached to the skin and fins of the fish. All Lernaea were adult females of Lernaea cyprinacea. The intensity of Gyrodactylus ranged from 1-2368 individuals per infected fish and the intensities of metacercarial cysts and Lernaea cyprinacea ranged from 1-80 and 1-5 individuals per infected fish respectively. Statistical analysis indicates that Gyrodactylus and metacercarial cysts had no specific preference sites on the gill. Caudal peduncle region of the fish was preferred by Lernaea cyprinacea. Results show that the oxygen consumption rates and blood haematocrit values of the host fish were not affected significantly by the presence of parasites at the current infestation level in spite of histopathological changes induced by the parasites on the infected sites of the fish.