Flavobacterium inkyongense isolated from ornamental cichlids

Authors: SEBASTIAO, FERNANDA DE - University Of California, Davis; Lafrentz, Benjamin; Shelley, John; STEVENS, BRITTANY - Aquarium Of The Pacific; MARANCIK, DAVID - Saint Georges University; DUNKER, FREELAND - California Academy Of Sciences; REAVIL, DRURY - Zoo/exotic Pathology Service; SOTO, ESTEBAN - University Of California, Davis

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2019
Publication Date: 6/14/2019
Citation: Sebastiao, F., Lafrentz, B.R., Shelley, J.P., Stevens, B., Marancik, D., Dunker, F., Reavil, D., Soto, E. 2019. Flavobacterium inkyongense isolated from ornamental cichlids. Journal of Fish Diseases. 42:1309-1313. https://doi.org/10.1111/jfd.13043.
DOI: https://doi.org/10.1111/jfd.13043

Interpretive Summary: In this study we report the isolation and characterization of Flavobacterium inkyongense from chocolate cichlids. Two chocolate cichlids presented with de-pigmented, erosive lesions, and several areas of de-pigmented scales along the flanks. The gills were friable, and areas of dark/light discoloration were observed. The clinical signs resembled those associated with columnaris disease, caused by the bacterium F. columnare. Skin lesions and gills were swabbed and inoculated onto modified Shieh agar to isolate the bacteria responsible for the lesions. Only a few mixed environmental/normal flora bacteria were recovered from the skin lesions; however, a moderate amount of F. columnare – like organisms were recovered from the gills of one chocolate cichlid. A single colony, referred to as R17-24B, was selected and examined in further detail using phenotypic and DNA sequencing methods to identify the bacterium. Sequencing of the 16S rRNA gene and a housekeeping gene, gyrB, revealed that the DNA sequences of R17-24B shared very high identity with F. inkyongense, thus identifying it as F. inkyongense. To confirm that F. inkyongense was the causative agent of disease in the chocolate cichlids, two studies were performed in which blue and hybrid tilapia were experimentally infected with the R17-24B isolate. In both studies, only a few tilapia mortalities were noted and F. inkyongense was not recovered from the kidney from these fish. Fish appeared in overall good health with only minor histopathologic findings. The current study reports the first association of F. inkyongense and fish infection. Although few mortalities were associated with F. inkyongense in laboratory-controlled challenges, future research investigating the virulence of F. inkyongense in other fish species and at different environmental conditions is warranted to clarify the pathogenicity of this bacterium. This is particularly important in aquatic environments such public aquaria or aquaculture facilities where other environmental and anthropogenic stressors can immunosuppress the fish host and allow infection by opportunistic organisms.

Technical Abstract: In this study we report the isolation and characterization of Flavobacterium inkyongense from chocolate cichlids. Two chocolate cichlids presented with de-pigmented, erosive lesions, and several areas of de-pigmented scales along the flanks. The gills were friable, and areas of dark/light discoloration were observed. The clinical signs resembled those associated with columnaris disease, caused by the bacterium F. columnare. Skin lesions and gills were swabbed and inoculated onto modified Shieh agar to isolate the bacteria responsible for the lesions. Only a few mixed environmental/normal flora bacteria were recovered from the skin lesions; however, a moderate amount of F. columnare – like organisms were recovered from the gills of one chocolate cichlid. A single colony, referred to as R17-24B, was selected and examined in further detail using phenotypic and DNA sequencing methods to identify the bacterium. Sequencing of the 16S rRNA gene and a housekeeping gene, gyrB, revealed that the DNA sequences of R17-24B shared very high identity with F. inkyongense, thus identifying it as F. inkyongense. To confirm that F. inkyongense was the causative agent of disease in the chocolate cichlids, two studies were performed in which blue and hybrid tilapia were experimentally infected with the R17-24B isolate. In both studies, only a few tilapia mortalities were noted and F. inkyongense was not recovered from the kidney from these fish. Fish appeared in overall good health with only minor histopathologic findings. The current study reports the first association of F. inkyongense and fish infection. Although few mortalities were associated with F. inkyongense in laboratory-controlled challenges, future research investigating the virulence of F. inkyongense in other fish species and at different environmental conditions is warranted to clarify the pathogenicity of this bacterium. This is particularly important in aquatic environments such public aquaria or aquaculture facilities where other environmental and anthropogenic stressors can immunosuppress the fish host and allow infection by opportunistic organisms.