Parasites of pike perch Stizostedion lucioperca (Linnaeus 1758) fry reared in two different types of natural food ponds in southern Finland

Abstract

Pike perch fry (<4 months old) reared in two different types of natural food ponds were examined for parasites in Rauma and at Porla, southern Finland, during June-August in 1990 and 1991. The ponds differed in size and drainage. The highest number of observed parasite species per sample was 11 at Porla and 4 in Rauma. Altogether 4 species of protozoan parasites were detected on the skin and/or gills: Ichthyobodo necator, Ambiphrya ameiuri, Trichophrya piscium and Trichodina sp. The two major species were I. necator and A. ameiuri. The intensity of I. necator infestation was mostly rather low. Infestation by A. ameiuri was very heavy at Porla in 1990. In July, the skin and particularly the fins were filled with this ciliate and the fins were frayed. Ten species of helminth parasites occurred at Porla: Diplostomum sp. (lens), Diplostomum sp. (vitreous humour), Tylodelphys clavata, Bunodera lucioperae, Proteocephalus sp., Eubothrium sp., Raphidascaris acus, Argulus foliaceus, Piscicola geometra and Nematoda sp. Only two helminth species, Diplostomum sp. in lens and Diplostomum sp. in vitreous humour, were found in the pike perch in Rauma. The composition of the parasite species and their influence on cultured pike perch in the natural food pond seemed to be connected to various environmental factors. Some indication was obtained for Ambiphrya ameiuri-induced mortality. The results of this study indicate that drainage of the pond between the growing seasons, minimizing the number of fish species in the pond and having sufficient nutrition are good methods for keeping the parasite load small.