This study determined the haematological changes in Korean cat¢sh, Silurus asotus, experimentally infected with Edwardsiella tarda. Twenty-four or 48 h after infection with 1 Â 10 4 colony-forming units (CFU) mL À 1 of E. tarda, the ¢sh were anaesthetized and the blood was collected. The haematological and biochemical tests included haematocrit (Ht), haemoglobin (Hb), leucocyte counts (Lc), total calcium (Ca), total protein (TP) concentration, alkaline phosphatase (ALP), glucose (GLU), aspartate aminotransferase, lysozyme and di¡erential leucocyte populations. After 24-and 48-h infection, the values of Ht, Hb, Lc, TP, ALPand GLU were signi¢cantly decreased with respect to the control. Aspartate aminotransferase and lysozyme activity in both the 24-and 48-h groups exhibited higher levels compared with those in the control. However, the bacterial infection did not induce any signi¢cant alteration in the Ca concentration. After the 48-h infection, neutrophils and macrophage populations were reduced whereas lymphocytes were increased with respect to those in the control and the 24-h infection groups. The present study demonstrates that E. tarda infection causes haemato-biochemical responses that are related to the general physiological condition and defence system in cat¢sh. Haematological changes in E. tarda-infected cat¢sh J H Yu et al. Aquaculture Research, 2010, 41, 295^302 Di¡erent superscript alphabets indicate a signi¢cant di¡erence among experimental groups (Po0.05). Ht, haematocrit; Hb, haemoglobin; Ca, calcium; TP, total protein; Lc, leucocyte counts. Aquaculture Research, 2010, 41, 295^302 Haematological changes in E. tarda-infected cat¢sh J H Yu et al.

Mass mortality of Korean catfish, Silurus asotus, occurred in a culture farm situated in Jeollabukdo Province, Korea. The cumulative mortality rates reached up to 5% of the total fish in the farm per day. In clinical signs, the affected fish showed abdominal distension, vent protrusion, enteritis, liver congestion and abscess‐like lesions in enlarged spleen and kidney. Histopathologically, in the liver, hepatocytes lost fat and underwent atrophy or necrosis. The spleen showed necrotized splenocytes and a haemorrhagic pulp. In the kidney, glomerular destruction, degeneration of renal tubular epithelial cell and haemorrhage were observed. However, necrotic muscular lesions were not observed. A pure bacterial isolate was obtained from the liver, spleen and kidney lesions of affected fish. Experimental infection of normal catfish with the isolate resulted in the development of clinical signs similar to those seen on the farm. The isolates were identified as Edwardsiella tarda through biochemical tests (99.4%) and analysis of bacterial genes (16S rDNA) sequences (98%). The bacteria possessed two virulent genes: sodB and katB genes. These results suggest that E. tarda can act as a pathogen of farmed catfish. This is the first report showing that E. tarda caused mortality in cultured Korean catfish.