A cross-sectional study was conducted to determine the occurrence of ecto- and endo-parasites of farmed Nile tilapia ( Oreochromis niloticus ) in Kericho, Bomet and Nakuru counties, Kenya. A total of 220 live tilapia were sampled from fish farms from Kericho (90), Bomet (60) and Nakuru (70) for postmortem examination and parasite identified using standard methods. Dissolved oxygen, pH, and temperature of water were measured in situ . Two liters of fish pond water were collected and taken to G overnment C hemist for spectrophotometry chemical analysis of phosphates , nitrites, nitrates, ammonia, salinity, turbidity, electrical conductivity, alkalinity and suspended solid particles. Over 39 % ( 39.54%, 87/220) of tilapia were infested by one or more parasite species. Ectoparasites recovered were protozoan ciliate species ; Trichodina on skin and fins; Riboscyphidia and Epistylis on the skin. Others, were monogenean Dactylogyrus species recovered from the gills and crustacean copepods recovered from the skin. Endoparasites included trematodes Diplostomum and Euclinostomum species recovered from the eyes and kidneys, respectively. In the abdominal cavity, there were Contracaecum while the intestines had the nematodes Paracamallanus and Camallanus species ; and the thorny worms ( Acanthocephalus species ) Prevalence of parasites per county were; Kericho 48.89% (44/90), Bomet 33.33% (20/60), and Nakuru 32.86% (23/70). Earthen ponds had a significantly higher (52.5%; 42/80) parasite infection relative to liner (35.45%; 39/110), plastic tank (30%, 3/10) and concrete (15%, 3/20) ponds (p<0.05). All water quality parameters were significantly different in all counties (One-way ANOVA, P<0.05) except salinity, sulphate, and nitrites (p>0.05). Sulphate had positive association of 1 (p<0.05) with Riboscyphidia , Epistylis , Trichodina , Contracaecum , Diplostomum , Dactylogyrus, Paracamallanus and Camallanus species. Electrical conductivity correlated with Trichodina , Euclinostoum , and Acanthocephalus species. Temperature , pH, nitrate, and phosphate had very strong association of (0.80-0.99, p<0.05) with most of the parasites. Phosphate and pH had moderately association of 0.6-0. 79 (p<0.05 ) and were correlated with Dactylogyrus , Camallanus, and Diplostomum species, respectively. Farmers are advised to monitor parasitism and water quality parameters and practice good aquaculture husbandry individually or through extension officers to mitigate parasitic infections.
Key words: Contracaecum , Diplostomum , monogenean, pond, tilapia, Trichodina