Aging changes in the liver of the male annual cyprinodont fish, Nothobranchius guentheri.

Histological studies were performed on the liver of the male annual cyprinodont fish, Nothobranchius guentheri between 3 and 18 months of age. The very young, but sexually mature fish, showed few changes. Beginning at 4–6 months of age the number of fish exhibiting histological changes increased, but reamined stable to 13–14 months. The prevalent changes were: vacuolization of hepatocytes and nodular degeneration progressing to cyst like formations. At 15–18 months, three new lesions were observed: swirl formations by endothelial cell proliferation, fibrosis with melanin pigmented cells and malignant transformation. Since annual fish have a relatively short lifespan, both in nature and in the laboratory, they have been used as a model for the aging process. Histological studies are critical in establishing aging patterns and allow for broader interpretation of physiological and biochemical changes.