The thymus of aging annual, cyprinodont fish, Nothobranchius guentheri and Cynolebias adloffi begins to undergo senescent changes at approximately four months. At this time, the histopathology reveals increased amounts of connective tissue, epithelial cysts and myoid cells, but decreased numbers of thymocytes. At 12 months, of the 50 fish observed at 10 stages from day 15 and 1, 2, 4, 6, 8, 9, 10, 11, 12 months the maximum time of senescence, there was an increased incidence of tumors in the oral cavity, connective tissue, kidney and liver in all 5 fish. At least in the kidney, the malignant transformation was classified as nodular-type histiocytic lymphoma. It is of interest that development of these tumors occurs during peak senescent changes in the thymus, supporting the view that as fish age, accompanied by atrophy of the thymus, the immune system is less vigorous and there is an increase in the incidence of cancer.
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The ultrastructure of prolactin cells in the annual cyprinodont Cynolebias whitei during its life cycle. A morphometric study in freshwater- and saltwater-reared fish.
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Department of Anatomy and Embryology, University of Nijmegen.
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Cell Tissue Res
September 1987
Department of Anatomy and Embryology, Catholic University, Nijmegen, The Netherlands.
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