Occurrence of larval contracaecum (nematoda: heterocheilidae) in three teleostean fish species from lake Naivasha, Kenya
Occurrence of the larval nematode (Contracaecum sp.) in three teleostean species, viz: Oreochromis leucostictus (Trewavas), Micropterus salmoides (Lecepede) and Tilapia zillii (Gervais) in Lake Naivasha was investigated over a period of 12 months (September 1996 - August 1997). The/ work was carried out to establish the seasonal prevalence, variation in intensity of infection with size, sex and sampling stations and the effect of the parasite on the health status of the three hosts. Results indicate that there was no significant monthly variation in the intensity of infection in the three fish species (P>0.05) and both males and females showed no significant difference in the rate of infection by the larval nematode. Oreochromis leucostictus was observed to be the most heavily infected (Mean parasite load = 15) while Tilapia zillii was the least infected (mean parasite load = 2) Infection rate and parasitic load between length classes were very significant in 0. leucostictus (X2 3 = 212.7; P<O.OOI), M salmoides (X2 3 = 12.93; P<O.OOI) but not in T. zillii (P>0.05). There was however, a great variation in infection rate within sampling sites in all the three species; 0. leucostictus (X2 4 = 20.66; P<O.OO1), T. zillii (X2 4 = 12.10; P<0.05) and in M salmoides (X2 4 = 18.89; P< 0.0 I). The nematode had no apparent effect on the well-being of the fishes as there was no significant relationship between condition factor and parasite load (P>0.05).