Microbial Load, Serum Enzyme Activity and Histopathological Alterations Induced by Aeromonas Hydrophilain in Experimentally Challenged Grass Carp

Aeromonas hydrophila is the main bacterial pathogen causing economic losses in fish during aquaculture. In this study, 587 grass carp were inoculated with the bacterial suspension of 2.5×1012 CFU/mL, and the mortality rate was 48.89% after 14 days. The fish infected with AH showed symptoms such as anal redness and swelling, eye congestion, fin hemorrhage, body surface congestion, ascites, liver and spleen hemorrhage, then died one after another 4 hours later. Within 24 hours after pectoral fin injection of AH, the microbial load in liver, spleen, kidney and gut were higher, while gill and muscle were lower. In addition, compared with the control group, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), fish C-reactive protein (CRP), fish serum amyloid A (SAA) and procalcitonin (PCT) levels were significantly changed (p<0.05). In histological sections, there were severe pathological changes in liver and kidney tissue:Significant steatosis of hepatocytes and renal cells, loss of renal tubular structure, glomerular atrophy, hepatocyte amyloidosis and intracapillary congestion occurred. This study will provide a research basis for further studies on host-pathogen interactions, therapy and epidemiology of Aeromonas hydrophila.