A case of ceroid deposition in the kidney of feral rainbow trout, Oncorhynchus mykiss, in Alicura impoundment, Argentina.

A severe case of ceroid deposition was observed in the kidney of a small number of feral Oncorhynchus mykiss from Alicura impoundment, Argentinian Patagonia. The pigments were observed intracellularly in the kidney tubules and in the parenchyma cells, varying from a large number of small droplets to one big droplet almost filling the cell and pushing the cytoplasm to one side of the cell. An extensive study of farmed fish, as well as wild specimens from the same impoudment, did not show any ceroid deposition. Further, no abnormal mortality rates were observed in the farms. The mechanism that caused this condition in just a small number of fish is not known.