Histological and cytological changes in the ovary of Cymatogaster aggregatus during gestation

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Abstract
Viviparity in the teleost fishes is most highly developed in the family Embiotocidae. In Cymatogaster aggregatus, a member of this family, the males are sexually mature at birth. Females born in June and July are inseminated soon after birth and carry the spermatozoa in the ovarian cavity until December when eggs are fertilized. Embryos are retained in the ovarian cavity till the following spring when they are born.The cells of the epithelium lining the ovarian cavity develop internal fluid reservoirs which reach their maximal stage in early gestation when there is an extensive sloughing of epithelial cells. The epithelium returns to its original condition in late gestation and later the cells undergo multiplication. The stroma becomes swollen and contains a large amount of fluid during early gestation and shrinks as the embryos become larger. Many of the eggs, failing to reach maturity at the time of fertilization, degenerate. Degeneration also takes place in numerous smaller ovocytes during gestation but some of them survive to grow during the next season.The cyclical changes in the ovarian tissue of Cymatogaster aggregatus are parallel to those which occur in the ovaries of the Goodeidae and the Jenynsiidae, two other families in which viviparity has been highly developed.