An Experimental Infection of Pseudomonas fluorescens and Its Effects on Hematology and Histopathology of Nile Tilapia, Ethiopia

Nile tilapia ( Oreochromis niloticus ) one of the commercially important fast-growing and well-adapted freshwater fish is cultivated extensively worldwide (FAO 2018). The present study was conducted on 36 apparently healthy Nile Tilapia (130 ± 10 g. body weight and average 19.5 cm length) collected from the National Fisheries and Aquatic Life Research Center (NFARC), Sebeta. Fish were adapted for one week in the experimental greenhouse of NFARC before starting the experiment Fish were divided into two groups (18 fish per each), inoculated intraperitoneally using 0.2 ml of saline, and the pathogen, Pseudomonas fluorescens at a concentration of 3 x 106 CFU/ml. The inoculated fish were observed for 21 days for pathogenicity. The clinical signs observed on the second day post injection were loss of balance, excessive mucus secretions on skin and gills, ascites with slightly protruded reddish vent, hemorrhages all over the body surface, frayed fins, and an empty intestine. This study showed that Pseudomona s infection caused 55.4% (10) mortality, with severe alterations in RBC and WBC counts with severe histopathological changes in muscle, gills, liver, kidney, spleen, and intestine. The histopathological changes observed include hemorrhages, tubular cell necrosis, congestion, mononuclear cell aggregation and infiltration in the kidney; hepatocyte vacuolization in liver; lamellar fusion in gills; sloughed and mucosal necrosis in intestine; mononuclear cell aggregation and infiltration in muscle and hemosiderin accumulation in spleen.