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Mortality and pathology of hybrid catfish, C larias macrocephalus ( G ünther) × C larias gariepinus ( B urchell), associated with E dwardsiella ictaluri infection in s outhern T hailand
Author(s) -
Suanyuk N,
Rogge M,
Thune R,
Watthanaphiromsakul M,
Champhat N,
Wiangkum W
Publication year - 2014
Publication title -
journal of fish diseases
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 85
eISSN - 1365-2761
pISSN - 0140-7775
DOI - 10.1111/jfd.12127
Subject(s) - edwardsiella ictaluri , catfish , biology , clarias gariepinus , microbiology and biotechnology , 16s ribosomal rna , histopathology , veterinary medicine , bacteria , fishery , pathology , fish <actinopterygii> , genetics , medicine , ictalurus
Abstract Enteric septicaemia of catfish ( ESC ) caused by E dwardsiella ictaluri is becoming an increasing problem in aquaculture and has been reported worldwide in a variety of fish species. This study reports ESC in hybrid catfish, C larias macrocephalus ( G ünther) × C larias gariepinus ( B urchell), cultured in s outhern T hailand. The bacteria were identified as E . ictaluri by conventional and rapid identification systems, as well as by genetic and phylogenetic characterization. Analysis of 16S r RNA indicated 100% homology to the 16S r RNA sequence of several E . ictaluri strains in G en B ank. Plasmid profiles demonstrated 4.0‐ and 5.6‐kb plasmids, compared with the 4.8‐ and 5.6‐kb plasmids in the US isolates, and representative genes of three of the four known pathogenicity islands of US isolates were present. Serologically, lipopolysaccharide ( LPS ) purified from the T hai isolates was not recognized by a monoclonal antibody against the LPS of US isolates. Fish experimentally infected with E . ictaluri showed 23–100% mortality within 14 days with a 168‐h LD 50 of 6.92 × 10 7 CFU mL −1 by immersion and a 96‐h LD 50 of 1.58 × 10 6 CFU fish −1 by intraperitoneal injection. Examination of tissue sections obtained from both naturally and experimentally infected fish indicated that infection of hybrid catfish with E . ictaluri produced lesions in several organs including liver, kidney, spleen, heart and brain. Histopathology findings included cellular necrosis, focal haemorrhage, infiltration of lymphocytes and multifocal granulomatous inflammation in the infected organs.