ASPECTS OF AGEING IN GUPPY, LEBISTES RETICULATUS (PETERS) .4. OVARY

Histological study of the changes in the ovary of a laboratory population of virgin guppies throughout their life cycle has distinguished three phases. The youngest fish had immature ovaries, with oocytes in various stages of development, but no ripe eggs were present. Sexual maturity and full reproductive capacity were reached between the ages of 8 and 12 months, when the numbers and size of ripe eggs achieved their maximum values. After this there was a gradual decline in the activity of the ovary, which was characterized by a decrease in the number of ripe eggs, by gradual infiltration of the ovary by connective tissue, and by thickening of the ovary wall. The number of atretic eggs present in the ovary increased with advancing age. The regression of the ovary was marked after the age of 30 months. Some of the ageing changes seen in the ovary of the guppy paralleled changes observed after the removal of the pituitary gland. However, other prominent features found in the senile ovary of Lebistes have not been commonly observed after hypophysectomy. The decrease in the functional activity of the ovary of the guppy with advancing age appeared to result from both a progressive decline in the function of the pituitary gland and autonomous ageing processes within the ovary itself.The findings are discussed in relation to the problem of the metabolic expenditure on reproduction in fish. © 1969.