First detection of Erysipelothrix sp. infection in western mosquitofish, Gambusia affinis, inhabiting channel catfish, Ictalurus punctatus, production ponds in Mississippi

Authors: STILWELL, JUSTIN - University Of Georgia; GRIFFIN, MATT - Mississippi State University; ROSSER, THOMAS - Mississippi State University; LEARY, JOHN - University Of Georgia; HAGEN-FREI, KATHARINA - University Of California; MISCHKE, CHARLES - Mississippi State University; POMARANSKI, ERIC - University Of California; SOTO, ESTEBAN - University Of California; CAMUS, ALVIN - Mississippi State University

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2019
Publication Date: 2/7/2019
Citation: Stilwell, J., Griffin, M., Rosser, T., Leary, J., Hagen-Frei, K., Mischke, C., Pomaranski, E., Soto, E., Camus, A. 2019. First detection of Erysipelothrix sp. infection in western mosquitofish, Gambusia affinis, inhabiting channel catfish, Ictalurus punctatus, production ponds in Mississippi. Diseases of Aquatic Organisms. 133:39-46.

Interpretive Summary: Native and introduced fish can serve as reservoirs for pathogens of cultured fish species. In the current study, 351 western mosquitofish Gambusia affinis collected from experimental catfish production ponds in Mississippi, USA, were surveyed to evaluate their potential to host fish pathogens. In addition to multiple parasites, 8 fish had widespread colonies of small Gram-positive bacteria. This bacteria was consistent with infections in ornamental fish cultured in the USA. Given the significance of commercial catfish aquaculture in the southeastern USA and the widespread distribution of mosquitofish in catfish ponds throughout the region, infectivity trials with channel catfish Ictalurus punctatus were conducted. Catfish fingerlings were exposed to the bacteria. No mortality was observed in catfish exposed, and surviving fish demonstrated no significant wounds, suggesting channel catfish have low susceptibility to the bacteria. Further research is warranted to investigate the susceptibility of other cultured fish species to this emergent fish pathogen.

Technical Abstract: Native and introduced fish can serve as reservoirs for pathogens of cultured fish species. In the current study, 351 archived western mosquitofish Gambusia affinis collected from experimental catfish production ponds in Mississippi, USA, were surveyed histologically to evaluate their potential as vectors for fish pathogens. In addition to epitheliocystis and multiple metazoan parasites, 8 fish had widespread basophilic colonies of small Gram-positive rods associated primarily with stroma supporting the skeletal muscle and bone, as well as connective tissue components of other tissues and organ systems, such as perivascular adventitia and basement membranes. These findings were consistent with spaC-type Erysipelothrix sp. infections in ornamental fish cultured in the USA. The 16S rRNA, gyrase B (gyrB), and surface protective antigen (spa) genes were amplified and sequenced from bacterial colonies excised from paraffin-embedded tissue sections using laser capture microdissection. Molecular data confirmed the identity of a spaCtype Erysipelothrix sp., which grouped phylogenetically with spaC-type Erysipelothrix sp. from diseased ornamental fish. Given the significance of commercial catfish aquaculture in the southeastern USA and the widespread distribution of mosquitofish in catfish ponds throughout the region, infectivity trials with channel catfish Ictalurus punctatus were conducted. Catfish fingerlings were exposed to a spaC-type Erysipelothrix sp. isolate by intracoelomic injection and gavage. No mortality was observed in catfish exposed by either route, and surviving fish demonstrated no significant histopathologic lesions, suggesting channel catfish have low susceptibility to the bacteria. Further research is warranted to investigate the susceptibility of other cultured fish species to this emergent fish pathogen.