Suspected sodium toxicity in hand-reared great blue heron (Ardea herodias) chicks

Sodium toxicity was suspected in hand-reared great blue heron (Ardea herodias) chicks fed herring frozen in brine (seawater). Affected chicks were lethargic with stiff legs that extended to the posterior, and breathing was labored. Chicks regurgitated food or refused to eat. All chicks that were fed herring exclusively and eight of the 10 chicks fed a mixed diet (herring and salmonids) died, whereas all chicks fed only salmonids survived. Renal lesions ranged from mild to marked generalized nephrosis, which was characterized by degeneration and necrosis of the proximal convoluted tubular epithelium and dilation of the distal convoluted tubules and collecting ducts. These observations suggest that fish frozen in brine is unsuitable food for hand-rearing of young herons.