Glomerular mesangial fibrosis in hatchery-reared rainbow trout (Salmo gairdneri)

Light and electron microscopic studies were performed on tissues of hatchery-reared rainbow trout (Salmo gairdneri) having a disease of currently unknown etiology with external symptoms of severe edema which causes increased mortality rate. Comparison with unaffected trout tissues revealed loss of cellularity in glomerular tufts with a replacement of mesangial cells by connective tissue. Ultrastructural studies showed the material to be collagen and established the diagnosis of glomerular mesangial fibrosis. The glomerular lesion was associated with alterations in lining epithelium of proximal tubules and extensive debris within tubule lumens. The findings are compared to glomerular lesions in mammalian and amphibian kidney.