High occurrence rate of xanthomatosis and nephrocalcinosis in aquarium-housed Atlantic wolffish Anarhichas lupus and spotted wolffish A. minor.

The Atlantic wolffish (AW) and the spotted wolffish (SW) are long-lived fish found in the North Atlantic and Arctic oceans and are respectively classified as special concern and threatened species, mainly due to fisheries bycatch. To better understand health issues associated with the care of these species in public aquaria, reports from all necropsies performed in 2 zoological institutions between 2009 and 2019 were reviewed (31 AW and 8 SW). These wolffish were fed with a similar fish-based diet and kept in multi-species exhibits with comparable environmental parameters. The most frequent necropsy findings were the presence of xanthomas (AW: 41.9%; SW: 75.0%), nephrocalcinosis (AW: 42.9%; SW: 75.0%) and urocystoliths (AW: 6.5%; SW: 62.5%). Xanthomas were mostly located at the base of pectoral fins and were characterized by extensive granulomatous inflammation centered on accumulations of partly mineralized degenerate fatty material, mainly composed of cholesterol crystals. Nephrocalcinosis was characterized by the deposition of calcium salts within the renal tubules and was commonly associated with tubular necrosis. The aquarium-housed wolffish were fed a coldwater fish-based diet. However, the natural diet of wolffish is composed mostly of invertebrates such as urchins and crustaceans. Differences in nutrient composition between these diets, such as lipid and mineral content, may have contributed to the development of xanthomatosis, nephrocalcinosis and urocystolithiasis in wolffish housed in these institutions.

A CLUSTER OF CASES OF THYROID HYPERPLASIA IN AQUARIUM-HOUSED TROPICAL MARINE TELEOSTS FOLLOWING A CHANGE OF SALT MIX BRAND.

Follicular thyroid hyperplasia was diagnosed in nine out of 32 (28%) marine tropical teleosts housed in a public aquarium over a 9.5-mo period. These proliferative lesions were considered to be the cause of death in five of these fish. Iodine concentration was undetectable in nonozonized water (<0.005 mg/L), suggesting that an environmental iodine deficiency was the cause of these hyperplastic thyroid lesions. The only significant modification in the husbandry was a change, 18 mo before the first case, of the commercial salt mix brand used to make artificial seawater. The iodine content in this replacement salt mix was five times lower than that of the salt mix used before. This case series suggests that the iodine concentration in this new salt mix was insufficient to maintain thyroid homeostasis in reef teleosts under the husbandry provided in this institution.