This study was initiated to obtain information about the natural history of the tule perch before greater reduction in population has occurred. The studies of Hopkirk (1962) and Turner (1966) did not include information on reproduction, development, and growth of embryos within the ovarian sac, and the growth of the tule perch and, secondly, to supplement the work of Hopkirk and Turner concerning color variation and food habits.

The natural cycle of reproduction in Cymatogaster aggregata Gibbons, a viviparous teleost, has been described and investigated experimentally. Laboratory manipulations of photo-period and temperature show that both are concerned with the environmental regulation of the cycle. The role of the pituitary was studied by the use of Methallibure, a chemical inhibitor of pituitary gonadotropic function. 3β— and 17β- hydroxysteroid dehydrogenases were localized in the gonads by histochemical tests and testicular steroids were partly identified biochemically. The role of androgens was studied with gonadectomized specimens and steroid replacement therapy. These various techniques indicate that increasing daylength in March and April stimulates production and/or release of pituitary gonadotropins and that the gonadotropins in turn initiate spermatogenesis and stimulate interstitial Leydig cells. The warm temperature of intertidal waters in addition to the long period of daily illumination from May to July accelerate spermatogenesis and testicular steroidogenesis. Increased gonadal androgen production, in turn, results in a modification of the male anal fin and brings on a full display of reproductive behaviour; some of the behaviour sequence, however, is controlled by pituitary gonadotropins. Restitution of the testes occurs in fall and winter. Oocyte formation appears to be enhanced by a lowered titre of gonadotropic hormones resulting from the warm temperatures of July and August. On the other hand, oocyte maturation in late autumn and early winter and gestation during early pregnancy require pituitary gonadotropins. / Science, Faculty of / Zoology, Department of / Graduate