Prevalence of parasitic infection in farmed nile tilapia, oreochromis niloticus (linnaeus, 1758) and other selected environmental factors associated with their transmission in winam gulf of lake victoria

Abstract

The general objective of the study was to assess the level of parasitic infection and farmer management practices in farmed Nile tilapia (Oreochromis niloticus) and some of the selected environmental factors associated with their transmission in Winam Gulf of Lake Victoria, Kenya. Selected water quality parameters from the 20 ponds, 30 cages and wild were measured in-situ using electronic meters and parasitological examination done according to standard procedures. A total of 96 questionnaires supplemented with direct observations were administered to fish farmers to assess the status of fish farming and management practices that could influence the occurrence of fish parasites. A total of 720 fish were purchased from fishermen, cage and pond farmers and examined for parasites. Temperature, DO, TDS and Salinity differered significantly in the different study areas (p<0.05) while pH registered an insignificant difference between the culture systems (pond and cage) and the wild (p>0.05). This was attributed to the homogeneinity of the study area experiencing the same climatic conditions. The environmental variables were within FAO’s recommended limits for fish production. The class trematoda which included: Gyrodactylus spp., Dactylogyrus spp., Tylodelphys spp., Diplostomum spp., Clinostomum spp. and Naescus spp. were the most common and prevalent parasites in both ponds and cages of the Winam Gulf while Amirthalingamia spp. and Diplostomum spp. were the most common and prevalent in the wild. This was due to the presence of piscivorous birds seen more often around and overstoking, which increases the spread and transmission of parasite from one fish to another. The parasitic infestation rate was not significantly different between the ponds and cages (p>0.05) while there was a significant difference between the two culture systems and the wild fish of Winam Gulf. Parasitism or parasitic infestation did not affect the fish condition factor in all the study areas. This was due to very low mean intensities recorded and shorter period of exposure to parasitic infestation as most farmers have not been to fish farming for a very long time especially the cage farmers. Some management practices identified as possible risk factors for occurrence of fish parasites included: overgrown vegetation, overstocking, failure to change water within a production cycle, cleaning and treatment after harvesting, poor quality feeds and feeding, sharing of farm equipments and materials, lack of awareness on fish parasitism and signs of the infected fish. For Kenyan national government to explore on blue economy and achieve the vision 2030 on food security and poverty reduction by 2030, efforts to promote commercial cage and pond fish culture enterprises in Winam Gulf of Lake Victoria and other water bodies must be enhanced on condition that the cages are sited in deep waters of the gulf with low cage concentration in a particular site and reduced stocking densities in order not to compromise the environmental quality.The farmers should also be equipped with proper management practices to maintain acceptable water quality and avoid transmission of fish parasites.