A 12-year retrospective study of 172 deceased captive syngnathids (Hippcampus kuda, H. abdominalis, and Phyllopteryx teaniolatus) from the Toronto Zoo was performed. The most common cause of mortality was an ulcerative dermatitis, occurring mainly in H. kuda. The dermatitis often presented clinically as ‘red-tail’, or hyperaemia of the ventral aspect of the tail caudal to the vent, or as multifocal epidermal ulcerations occurring anywhere. Light microscopy often demonstrated filamentous bacteria associated with these lesions, and it was hypothesized that the filamentous bacteria were from the Flavobacteriaceae family. Bacteria cultured from ulcerative lesions and DNA extracted from ulcerated tissues were examined using universal bacterial 16S rRNA gene primers. A filamentous bacterial isolate and DNA sequences with high sequence identity to Cellulophaga fucicola were obtained from ulcerated tissues. Additionally, in situ hybridization using species-specific RNA probes labeled filamentous bacteria invading musculature at ulcerative skin lesions.