Aging changes in the kidneys of two poeciliid fishes, the guppy Poecilia reticulatus and the Amazon molly P. formosa.

Histological surveys of the kidneys of two poeciliid fishes, the Amazon molly Poecilia formosa and the guppy P. reticulatus, throughout their lifespans showed no regular aging trends. Few kidney lesions were found in the Amazon molly until very late in life, 60 months or more, when obsolescent glomeruli and dilated renal tubules occurred. Guppies showed involutional changes of the renal system earlier, and the lesions became more severe with age, particularly in male fish. Hemopoietic tissue was reduced in amount in older fish of both species. Guppies of a year and older had marked accumulation of melanin in the melanomacrophage centers of the kidney, and the amount present increased with age. By contrast, there was little melanin deposition in mollies until almost the end of the lifespan. Hyaline droplets were consistently seen in the renal tubules of the mollies, but were rare in guppies. The degenerative changes in the kidneys of these two teleosts are similar to those seen in the kidneys of aging mammals. Despite the loss of normal structure in older fish, it seemed unlikely that degeneration of the kidney was directly involved in aging and death.