Abstract
Seahorses are part of the family of fish, Syngnathidae, which also includes pipefish, pipehorses and seadragons. Due to elevated morbidity and mortality rates in syngnathids at the Toronto Zoo and relatively few disease publications pertaining to this family of fish, a 12 year retrospective study of diseases in syngnathids at this institution was undertaken. This study included over 170 cases and three species of syngnathids (Hippocampus kuda, Hippocampus abdominalis, and Phyllopteryx teaniolatus). Major causes of morbidity and mortality were summarized in a case report, with the most common cause found to be an erosive to ulcerative dermatitis, occurring mainly in Hippocampus kuda species and accounting for almost 25% of all cases. This dermatitis often presented clinically as 'red-tail', a common term used to describe the hyperaemic ventral aspect of the entire length of the tail caudal to the vent. A second clinical presentation or suspected progression of 'red-tail' was multifocal epithelial ulcerations occurring anywhere along the body but usually involving the tail. The consequences of ulcerative skin lesions in fish are significant because the epidermis and dermis not only act as a barrier against external pathogens, but also limit significant shifts of water from the fish to the external environment in the case of marine fish. Histopathology of seahorses with ulcerative lesions often demonstrated filamentous bacteria associated with these lesions. While ulcerative lesions are common in syngnathids, we usually associate these with Mycobacterium, Aeromonas and Vibrio speciesand these are not filamentous bacteria.1,3,7 In other fish, filamentous bacteria associated with erosive to ulcerative lesions include many species of the Flavobacteriaceae family such as Flavobacterium psychrophilum and Tenacibaculum maritimus.2,4-6 It was therefore hypothesized that the filamentous bacterium observed under light microscopy within ulcerative lesions was the etiology of the ulcerative dermatitis. One of the objectives of this project was to culture bacteria from erosive to ulcerative lesions prospectively for bacterial identification via biochemical testing and PCR using universal 16S rRNA gene primers. These results were compared to environmental bacterial cultures and bacterial microflora from the skin of clinically normal seahorses. In attempt to link back the results of bacterial cultures to the histological lesions, PCR on formalin-fixed tissues using universal 16S rRNA gene primers was conducted to amplify bacterial DNA within lesions. Additionally, species-specific RNA probes were used for in situ hybridization to localise the bacterial RNA within lesions under light microscopy. Current results suggest that bacteria of the Flavobacteriaceae family are associated with the lesion; the evidence to this effect include the filamentous morphology of the bacterium under light microscopy, culture of the organism from lesions, absence of this bacterium in healthy animals and the environmental samples and positive PCR for Tenacibaculum species from some ulcerative tail lesions.
Acknowledgements
The authors would like to thank the Toronto Zoo staff for their help with data collection, care for the animals and discussions. Thank you to the Fish Pathology Laboratory staff for help with processing samples. Funding for V.L. was provided by the Morris Animal Foundation and the OVC Fellowship while funding for the project was provided by the OVC Pet Trust Fund and Morris Animal Foundation.
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