Seasonal occurrence of metazoan parasites in Tigerfish, Hydrocynus vittatus Castelnau, 1861 (Characiformes: Alestidae) from Sanyati Basin, Lake Kariba, Zimbabwe

Lake Kariba is a tropical lake with slight variations in seasonal temperature. Temperature is an important physical variable in the biology of both fish and their parasites. Currently, there is no information on the seasonal occurrence of fish parasites in Lake Kariba. The objective of this study was to investigate the seasonal occurrence of metazoan parasites in Hydrocynus vittatus in Lake Kariba, Zimbabwe. Twenty fish specimens were collected by seine netting per season between October 2014 and July 2015 in the Sanyati Basin, Lake Kariba, and examined for metazoan parasites. Mean water temperatures ranged from 24.1 °C to 31.2 °C with slight variations between the seasons. Metazoan parasites consisting of Monogenea (Annulotrema pikei, Annulotrema pseudonili, Annulotrema bracteatum), Nematoda (Contracaecum larvae), Copepoda (Lamproglena hemprichii), Cestoda (larval cestodes, Ichthybothrium sp.) and Pentastomida (pentastomid larvae) were recorded. Larval cestodes were recorded in autumn and spring, while pentastome larvae were recorded in summer and spring. The Ichthybothrium sp. was recorded once in winter. Annulotrema pikei and A. pseudonili were observed on the gills and A. bracteatum on both the gills and the skin. Contracaecum larvae, L. hemprichii and A. bracteatum (from the skin) were recorded in all the seasons, with slight variations in prevalence, mean abundance and mean intensity. However, these variations were not statistically significant (analysis of variance or ANOVA, p > 0.05). The slight variations in occurrence of the parasites were probably because of the thermal stability of the lake where variation in temperature was small between seasons. Both A. bracteatum and Contracaecum larvae were aggregated on the fish host, whereas L. hemprichii exhibited a random distribution. Parasite diversity was at its highest during winter.