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.

Isotopic Discrimination (δ15N, δ13C) in Captive and Wild Common Murres (Uria aalge) and Atlantic Puffins (Fratercula arctica).

Studying the diet of consumers using stable isotopes provides insight into the foraging ecology of individuals and species. To accurately reconstruct the integrated diet of animals using stable isotope values, we must quantify diet-tissue discrimination factors (DTDFs), or the way in which stable isotopes in prey are incorporated into the tissues of consumers. To quantify DTDFs, controlled experiments are needed, whereby consumers are fed a constant diet. However, relatively few controlled-diet studies have been conducted for seabirds. In this study, captive adult Atlantic puffins (Fratercula arctica) and common murres (Uria aalge) were fed a two-source diet of capelin (Mallotus villosus) and Atlantic silverside (Menidia menidia) to determine the DTDFs for the cellular component of blood and plasma for both δ15N and δ13C. The DTDFs for the cellular component (Δ15N: 2.80±0.28; Δ13C: 1.21±0.22) and plasma (Δ15N: 1.72±1.03; Δ13C: -0.18±0.56) of puffins were similar to those for the cellular component (Δ15N: 2.91±0.18; Δ13C: 1.09±0.23) and plasma (Δ15N: 2.18±0.77; Δ13C: -0.70±0.18) of murres. We reconstructed the diet of wild murres and puffins breeding on the northeastern coast of Newfoundland using previously published DTDFs and estimated DTDFs from our feeding experiment. Reconstructed dietary proportions supported a priori knowledge of diet, although outputs were sensitive to the DTDF used. Despite the similarity of our DTDFs for puffins and murres, along with the similarity of our DTDFs with those of other seabird species, our sensitivity analysis revealed considerable differences among resultant dietary contributions from mixing models, further highlighting the importance of using species- and tissue-specific DTDFs to enhance knowledge in the foraging ecology of seabirds using stable isotopes.