A quaculture is the fastest growing food production sector in the world. In Africa’s food systems, fish and other aquatic foods play a multifaceted role in generating income and providing a critical source of essential micronutrients. Kenya is ranked the fourth in aquaculture in Africa and is endowed with a vast network of aquatic resources comprising freshwater lakes, rivers, and an extensive ocean resource base. Fisheries and aquaculture sector in Kenya contributes about 0.8% to the Gross Domestic Product (GDP) but it faces severe losses due to bacterial diseases among them being Aeromonasis.
This study determined the lethal dose (LD50-240h ) of A. veronii biovar sobria and also investigated the clinicopathological changes after intraperitoneal inoculation of Nile tilapia (Oreochromis niloticus) (n=80). Post-fingerlings fish specimens (15±5g) were inoculated with 0 (control), 1.5x104, 1.5x105, 1.5x106, 1.5x107, 1.5x108 and 1.5x10 9 CFU/ml for the determination of LD50. The lethal dose (LD50-240h ) of A. veronii biovar sobria was found to be 1.5x108 CFU/ml. Typical clinicopathological changes of A. veronii biovar sobria were observed and included: darkening of the skin (16.25%), hemorrhages over the body surface (21.25% ), scale loss exposing the underlying skin at the base of caudal fin (13.75%), hemorrhages and enlargement of the liver (22.5%), congestion and enlargement of the spleen (22.5%), ascites (17.5%), distended gall bladder (20%), congestion on the operculum (20%), congested and hemorrhagic gills (15%), inflamed vent (13.75%) , erosion of the fins (6.25%), cloudiness of the eye (32.5%), exophthalmia (18.75%), increased mucus on the skin surface (13.75%), erratic movement with loss of balance (42.5%), reduced feed consumption (48.75%), swimming at the bottom of the aquarium (40%), irregular breathing (20%) and lethargy (41.25%). There was 85.71% mortality in 1.5x109 CFU/ml inoculation group within 48 hours of inoculation and 55%, 30.43%, 14.28% and 5.88% mortalities in 1.5x108, 1.5x107, 1.5x106 and 1.5x105 CFU/ml inoculation groups respectively between day 3 and day 9 of experiment. However, there was no mortality in 1.5x104 CFU/ml and 0 CFU/ml inoculation group. It is recommended that more studies should be conducted on the pathogenicity of A. veronii biovar sobria to help formulate better management protocols in fish farming.
Key words : Aeromonas veronii biovar sobria. Aquaculture. Lethal dose (LD50) . Nile tilapia. Inoculation. Clinicopathological.