Age and growth of the shiner perch, Cymatogaster aggregata Gibbons, were analysed with the aid of scales taken from fish obtained at Keates Island, British Columbia, in 1963 and 1964. Cymatogaster exhibits a relatively constant relationship between scale growth and increment of body length throughout its life and based on this observation a new method of back-calculation was developed. The scales of Cymatogaster may have up to three different types of checks, birth checks or metamorphic annuli, spawning checks, and annuli. The highest levels of instantaneous growth rates occurred during the spring and early summer, between the time of formation of an annulus and the following spawning check. It is during this period that water temperatures reach a maximum and food is most abundant. The lowest instantaneous growth rates occurred during the fall and winter months between the formation of a spawning check and the following annulus. Seasonal and diurnal movement patterns exhibited by Cymatogaster were studied by means of extensive gill net sets in 1963 and 1964 at the Keates Island study area. The fish first moved into the area in early June and left again by mid-October. In June, just prior to spawning, Cymatogaster exhibited a pattern of diurnal movement that involved migration from deep to shallow water during the day, and from shallow to deeper water at night. After the spawning period there was a complete reversal of the diurnal movement pattern. Light intensity appeared to be the most important factor governing the onshore and offshore movements of Cymatogaster. Stomach content analysis indicated that by volume, mussels and algae were the most important items in the diet of Cymatogaster, although barnacles and zooplankton were sometimes eaten in large quantities. Yearling Cymatogaster fed actively throughout the time they were present in the study area but mature fish exhibited a marked reduction of feeding during the spawning period. The initiation of feeding was governed primarily by an increase in light intensity associated with sunrise, and little or no feeding occurred during the hours of darkness. Data indicated that the rate of passage of food through the digestive tract varied between adults and yearlings, as well as seasonally. The relationships between age and growth, seasonal and diurnal movement patterns, and feeding habits and food preferences of Cymatogaster were correlated and related to factors of the physical and biotic environment. / Science, Faculty of / Zoology, Department of / Graduate

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