1National Zoological Park, Smithsonian Institution, Washington, DC, USA; 2Mystic Aquarium, Mystic, CT, USA; 3Department of Environmental and Toxicologic Pathology, Armed Forces Institute of Pathology, Washington, DC, USA; 4Department of Hepatic Pathology, Armed Forces Institute of Pathology, Washington, DC, USA
Two female northern fur seals (Callorhinus ursinus) (NFS) and two female California sea lions (Zalophus californianus) (CSL) from the Mystic Aquarium, the Smithsonian National Zoological Park, and Seneca Park Zoo died with similar clinical and pathologic findings. Livers showed necrosis and/or nodular regeneration with cirrhosis associated with high levels of iron within hepatocytes, Kupffer cells, and macrophages. Livers from these and other captive and wild otariids were compared histologically using hematoxylin and eosin stains and Prussian blue stain for iron. Histologic iron content was subjectively graded from 0–4+ with the following results: captive adult animals with histologic and gross lesions had levels of 3+–4+. Captive seal pups had levels from 1+–3+, and wild cases had levels from 0–2+.
Paraffin-embedded liver samples analyzed for iron and copper content by atomic absorption spectrophotometry varied from 10,700–27,000 µg iron/g dry weight in captive adults. This compared with ranges of 364–872 µg iron/g dry weight in wild harvested fur seals with histologically normal livers. Copper levels ranged from 6–193 µg copper/g dry weight in captive NFS and from 61–111 µg copper/g dry weight in wild harvested NFS with histologically normal livers.
Serum iron profiles from 16 fur seals and 3 sea lions in adult females ranged from 72–341 µg/dl of iron, with total iron binding capacity (TIBC), from 100–286 µg/dl, and percent saturation from 31–100%. In males and NFS pups, serum iron levels ranged from 77–162 µg/dl; TIBC from 198–368 µg/dl; and percent saturation from 22–72%.
These data indicate that in captive female otariids iron accumulation is a pathologic process that may lead to hemochromatosis. Further evidence suggests that increased dietary bioavailability of iron may result from a higher proportion of fish fed than cephalopods in captive otariid diets.