The prevalence of Crustacean parasities on Nile Perch (Lates niloticus) and Nile Tilapia (Oreochromis niloticus) in Lake Kyoga, Uganda.

Abstract

A study to investigate the prevalence and distribution of crustacean ectoparasites on the commercial fish species, Nile perch and Nile tilapia in Lake Kyoga, Uganda, was conducted through a survey for six months starting from February 2007 and ending July 2007. Crustacean ectoparasites are common parasites of fresh water fish and are known to cause detrimental effects to their hosts. Therefore the study particularly sought to provide information on the identity and intensity of the crustacean parasites infesting major commercial fish from Lake Kyoga of which little has been done and documented.

Data was collected from inshore and offshore of each of the following sampling stations: Iyingo, Bukungu and Lwampanga once a month. A total of one thousand two hundred and seventy (1270) fish were sampled and examined for copepod ectoparasite. Six hundred and twenty nine (629) fish were Nile tilapia and six hundred forty one (641) were Nile perch.

The findings showed that Oreochromis niloticus from Lake Kyoga was highly infested by crustacean ectoparasites of genus Lernaea and insignificantly infested with Dolops spp. However, Nile perch was found free of those parasites. The Lernaea parasites mostly occurred on the skin surface and rarely found on the inner lining of the operculum, gills and fins.

Generally, incidence and intensity of infestation increased with size of the host. Size class of 30 - 34.9 cm (TL) was found to be the most infested followed by size class 25 - 29.9 cm (TL). Immature fish (juveniles) were free from any ectoparasite. There was no significant difference in the levels of infestation between the fish samples taken from inshore and offshore waters, different sampling stations or in different sexes.

The study concluded that there was high parasite infestation of fish in Lake Kyoga where Oreochromis niloticus was mostly infested with crustacean ectoparasite, Lernaea sp. The level of infestation was comparable in both sexes of fish. The study recommends that the level of infestation by Lernaea and Dolops on fish in Kyoga be monitored and environmental friendly measures be adopted to control incidence of the parasites in the lake. It also recommends that the effects of these crustaceans on fish and on public health be investigated.