Effect of water quality on the parasite assemblages infecting Nile tilapia in selected fish farms in Nakuru County, Kenya

Abstract

Aquaculture has been documented as the most developing food industry in Kenya with increased production since the Government initiated Economic Stimulus Programme (ESP) in 2009. However, the production has not been to a maximum level anticipated in the country, particularly in Nakuru County. This is due to the uncontrolled addition of inputs (Inorganic fertilizers, manure and fish feeds) that deteriorate pond water quality. Poor water quality is one of the most common challenges faced by fish farmers since it impedes fish production and increases the incidences of parasite infections in cultured fish, leading to extensive losses. Therefore, this study investigated the effect of water quality on parasite assemblages infecting Oreochromis niloticus Linnaeus 1758 in selected fish farms within Nakuru County, Kenya from November 2016 to February 2017. A semi-structured questionnaire was administered in each fish farm to gather information on the farm management strategies. Selected physico-chemical parameters namely: dissolved Oxygen, temperature, pH, conductivity and turbidity were measured in situ using appropriate meters. Water samples from each fish farm were analyzed for nutrients (ammonium, nitrite, nitrate, total nitrogen, soluble reactive phosphorus and total phosphorus) using American Public Health Association (APHA) standard methods. Fish samples were killed by decapitation and examined in the laboratory for ecto- and endoparasites using a compound microscope and the parasitological parameters (prevalence, mean intensity, mean abundance and diversity) calculated. The results indicated that the water quality parameters were significantly different for all the six fish farms (P<0.05). The species of parasites also varied from one fish farm to another. The total number of parasite species recorded during this study were 15, with the highest number of species recorded in Subukia (10 species) and the lowest in Dundori (3 species). The parasite assemblages varied with the water quality parameters between fish farms. Out of 300 fish sampled, 252 were infected by parasites representing an overall prevalence of 84 % with the highest mean intensity of ectoparasites, particularly monogenean parasites compared to the endoparasites encountered during the study. Trichodina sp and Cichlidogyrus halli were found in all the studied fish farms. There was a positive correlation between water quality parameters and parasite infection levels. This study also recorded a positive correlation between fish size classes and the parasite infection levels (r² =0.3). The Fulton’s condition factors of parasitized and non-parasitized Oreochromis niloticus showed no significant differences statistically (P>0.05). The fish farms with poor water quality recorded many species of parasites infesting O. niloticus compared to others which recorded good water quality parameters. Therefore, regular monitoring and control of water quality in fish ponds is recommended to reduce levels of parasite infestations.