Mortality of Clarias gariepinus caused by Aeromonas caviae and nitrite toxicity in a fish farm

Abstract

In Nigeria, farming of freshwater fish, mainly that of Clarias gariepinus has gained prominence as means of improved protein supply and livelihood. Many farmers suffer untold losses in their bid to make a living from commercial fish production. Among the major causes of infectious disease outbreaks in fish farms are pathogenic bacteria of the genus Aeromonas. This is a case report of outbreak of Aeromonas caviae infection complicated by nitrite toxicity in Clarias gariepinus. Carcasses of 17 African catfish juveniles and two water samples were presented to the poultry and fish clinic of the Veterinary Teaching Hospital, University of Jos for investigation. The fishes had been on medication (Fish cure antibiotic +®) for over 5 days with cumulative mortality of 230 out of 2,500 fishes (9.2 %). Necropsy was conducted and samples were taken for microbial analysis and histopathology while water samples were subjected to chemical analysis. Gross lesions were broken barbels, cutaneous depigmentation, branchial pallor, ascites, renal and splenic congestion. Histologically, there was dissociation of hepatic cords, necrosis of hepatocytes with vacuolation and mononuclear cellular infiltrations. Also, there was renal tubular epithelial necrosis with mononuclear and heterophilic infiltration while micro abscesses were observed in the brain. Marked Zenker’s necrosis and edema were seen in the skeletal muscles. Organism isolated from livers and kidneys was identified as Aeromonas caviae and was susceptible to enrofloxacin, furaltadone and florfenicol. Nitrite in fish pond water was 1mg/L. Bath medication with enrofloxacin at 33mg/litre of water for 6 hours treatment per day was done to reduce the mortality. The farmer was advised to change the source of water for the fish pond immediately. It is recommended that to avoid losses in fish farming, farmers should check the quality of water intended for use on fish farms and ensure early health check on fingerlings purchased for rearing.