GRANULOMATOUS MYOSITIS IN RAINBOW-TROUT ONCORHYNCHUS-MYKISS AFFECTED BY PROLIFERATIVE KIDNEY-DISEASE (PKD)

A hatchery for brown (Salmo trutta) and rainbow (Oncorhynchus mykiss) trout has been repeatedly affected by proliferative kidney disease in summer. Rainbow trout was the only species affected, showing lesions p rincipally in the kidney and in the red muscle of both lateral lines. Grossly, fish had protuberances in the kidney and on the skin surface corresponding to granulomatous inflammation of the kidney and of the r ed muscle, respectively. PKX cells were observed in granulomatous tiss ues of both muscle and kidney and were composed of macrophages, lympho cytes and plasma cells. Using lectin GS-I, extrasporogonic stages of m yxosporean PKX cells were recognized in the kidney and muscle.