Pathogenicity and infectivity of Saprolegniaceae species in Cage Aquaculture Establishments of Oreochromis niloticus in the Nyanza gulf of Lake Victoria Kenya

Lake Victoria Kenya has recorded a steady decrease of the capture fishery in the past two decades which has conversely led to an increase in investments in the cage aquaculture in equal measure probably to fill the gap. Regrettably, reports of massive fish kills and associated huge economic losses through decreased quality and quantity of yields has not been infrequent. Leading suspects have been water quality, inadequate biosecurity measures, and mixed bacterial and fungal pathogens. The aim of this investigation was to inspect and identify the fungal pathogens present in the fresh carcass as well as in the dying fish during a reported mass mortality of Oreochromis niloticus. Samples were collected mainly in the small-scale establishments that were comparatively adversely affected in the four Counties; Siaya, Kisumu, Homa Bay and Migori with the cooperation of the fish cage owners and the beach management officials at the said sites. The images of the observed fungal patches, greyish in colour likely due to the presence of additional secondary bacterial contaminants and debris were taken using a Nikon D7500 DSLR Camera. Mortality range (minimum – maximum) was 40% to 95%. Identification and characterization of the fungus which focused on the most common Saprolegniaceae, was done in the laboratory by use of authentic manuals. Mortality of fish due to osmoregulatory failure and the possible role of release of Saprolegnia toxin in producing internal organs pathology has been discussed.