A histological assessment of damage in rainbow trout, Salmo gairdneri Richardson, fed rations containing erythromycin

Abstract. Rainbow trout fed prepared rations containing therapeutic levels of erythromycin (110 mg/kg daily) developed lesions in epithelial cells of the first proximal segment of the nephron. Pathological changes which developed within 24 h were characteristic of congestive overloading of lysosomes. Treated fish became anorexic within 2–3 weeks. Affected epithelial cells offish after 14 days of anorexia contained residual bodies in an otherwise normal appearing cytoplasm. Cell injury was reversible. Since the onset of anorexia corresponded with the completion of the recommended treatment period and damaged cells repair rapidly, erythromycin should nevertheless be retained as the treatment of choice for bacterial kidney disease.