Aquatic Medicine Laboratory, Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University
Blacksburg, VA, USA
Steatitis has been widely observed in mammals and only sporadically reported in fish.1 This condition has been attributed to improper nutrition, and its incidence in fish may increase because cultured foodfish are increasingly maintained on a single-source diet. Thus, fish become more susceptible to the effects of food oxidation and dietary insufficiencies. Subsequent malnutrition may be accentuated in newly cultured foodfish species, such as yellow perch (Perca flavescens), for which dietary requirements have not been fully elucidated.2
Adult yellow perch from an indoor recirculation aquaculture facility were submitted to the Aquatic Medicine Laboratory with chief complaints of chronic mortalities, external lesions, and abdominal distension. Fish exhibited diffuse petechiae and ulcerations on the skin. Skin and fin scrapes demonstrated mixed bacterial populations and rare fungal hyphae, while gill clips showed moderate telangiectasia and moderate mucus production. Internal examination exhibited over-inflated swim bladders and excessive amounts of firm, mottled reddish-brown-to-white adipose tissue filling the abdominal cavity. Bacterial culture revealed mixed isolates of Aeromonas sp., Pseudomonas sp., Shewanella sp., and Vibrio sp. from the brain, posterior kidney, and skin lesions. Histologic evaluation of sampled tissues demonstrated mild-to-moderate hyperplastic branchitis associated with filamentous bacteria among the gill lamellae. Coelomic adipose tissue had coalescing granulomatous inflammation with extensive deposition of acid-fast material (ceroid/lipofuscin) in macrophages. All other observed organs appeared normal. Based on these clinical findings, a diagnosis of granulomatous steatitis with secondary bacterial infection was made.
1. Guarda F, G Bertoja, I Zoccarato, E Tartari, B Biolatti. 1997. Spontaneous steatitis of epicardial fat in farmed white sturgeon (Acipenser transmontanus). Aquaculture 158: 167-177.
2. Speare DJ. 1998. Non-infectious disorders associated with intensive aquaculture. In: Leatherland JF, PTK Woo (eds.). Fish Diseases and Disorders, Volume 2: Noninfectious Disorders. CAB International, New York, New York, Pp. 303-333.