An overview of fish disease and parasite occurrence in the cage culture of Oreochromis niloticus: A case study in Lake Victoria, Kenya

Cage aquaculture has been on a steady rise in Lake Victoria, Kenya, since 2016, resulting in the current culturing of over 3,600 cages of Tilapia (O. niloticus) (Orina et al., 2018). Unfortunately, there has been limited, if any, focus on fish health aspects. Rise in intensification and commercialization predisposes fish stocks to disease due to rise in stress levels and consequent reduction in the fish immunity. Nutrient rich surroundings create a conducive environment for rapid proliferation of bacterial and saprophytic fungal growth leading to net clogging and consequently a low biological oxygen demand. Such conditions predispose the stocks to infections. This study was conducted to provide a baseline analysis of the health conditions/status of the cultured fish in this region. It encompassed studies from 2016 to 2018 on tilapia of the genus O. niloticus using both experimental (using standard procedures and protocols) and socio-economic studies (using structured questionnaires, see annexure 1). Results found the following occurrences; bacterial infections (10%), fungal infestations (12.5%), myxosporean parasites in the gills (5%), parasitic copepods (10%) and fin rot (2.5%) in the stocks. There were no significant differences between abiotic parameters in the cage locations and the wild (p > 0.05). Additionally, 90% of the respondents had no fish disease training or clue on the treatment action necessary whenever fish diseases struck. Findings from this study put to the fore the significance of fish diseases in a cage culture system in light of commercialization of the industry and the importance of biosecurity and maintenance of optimal environmental conditions within the scope of Blue Economy growth in this region. This study did not detect any disease or parasite of zoonotic importance.