ENVIRONMENTAL AND HORMONAL CORRELATES OF GONADAL FUNCTION IN THE FISH: Cyprini on watsoni

Abstract

Studies were conducted to assess role of photoperiod and temperature in regulat i on of gonadal developme nt and function during annual reproductive cycle in the fish, Cyprinion watsoni (Family: Cyprini d ae ) . In addi.tion, to seasonal variations in gonadal steroids and changes following experimental exposure of fish to photoperiod-temperature regimes were studied. Also selected stages of ovarian follicles were examined with the e l ectron microscope in an attempt to relate environmental and hormonal events in the light of ~orphologica l fea tures of the follicles. The perinucleolus stage follicle lacks d efinitive theca and granulosa. A vitelline envelope makes its appearance first in late perinucleolus stage evidently through deposition of material from the prefollicular cells surrounding the oocyte. Cortical alveoli characterize the cortical alveolar stage follicles which too lack definitive theca and granulosa layers. The prefollicular cells appear active in formation of zona radiata interna and externa. The presence of certain special cells which appear physiologically more active than other cells in prefollicular envelope has been noted in the perinucleolus and cortical alveolar stage follicles. Theca and granulosa and a fully d e v e loped vitelline envelope with three d is tinct layers are first s een in the yolk stage f ollicles. The organization of follicles and subcellular features of the theca and the granulosa cells have been discussed in relation to steroidogenesis. In order co Study effects of photoperiod and temperature the fish were exposed in the laboratory to fou~ photoperiod-temperature regimes, namely, long photoperiodwarm and low temperature o 0 (15L/9D:25 C or 15 C), short photoperiod-warm or low temperature o 0 (9L/15D:25 C or 15 C) in preparatory, prespawning, early spawning and postspawning seasons. The results snow that a long photoperiod -wa~m temperature combilaation is essential for causing gonadal recrudescence in the preparatory and prespawning seasons. Short photoperiod and warm temperature cause gonadal regression in the preparatory season whereas short photoperiod and low temperature retard gametogenesis 1Il the prespawning season. In the spawning season, warm temperature alone regardless of photoperiod stimulates spawning. Low temperature in either photoperiod supports vitellogenesis in the females and checks spawning in the male. Low temperaturelong photoperiod and low temperature-short photoperiod are important in initiating gonadal recrudescenc~ in the female and the male respectively in postspawning season. The gonadal response, thus, varies with the seasonal history of t~e fish. Both photoperiod and temperature are important 1n controlling gonadal function in Cyprinion watsoni. It was possible in this study to measure only three gonadal steroids; estradiol and progesterone in the female and testosterone in the male. Their levels varied seasonally. These steroids in the gonads increased to peak values in April (early spawning period) before declining to basal levels in the postspawning period. The levels of testosterone paralleled the variations in the testis but plasma progesterone continued to rise in the postspawning season (June) before finally declining to basal level. In the preparatory season, ovarian estradiol and progesterone increased only in the long photoperiod-warm temperature regime. Testosterone in the testis increased in long photoperiod at both warm and low temperature. In the prespawning season, ovarian estradiol increased again in the long photoperiod-warm temperature regime, progesterone increased at both warm and low temperature in long photoperiod. Testicular testosterone increased maximally in short photoperiod. In the postspawning season, highest levels of estradiol were observed in the long photoperiod-warm temperature condition. Progesterone increased but insignificantly in long and short photoperiod at both temperatures. Testosterone increase in all experimental groups with the greatest increase occurring in the long photoperiod-low temperature regime. The observations on hormone profiles have been examined in the light of information available for other species of fish, in relation to gonadal stages, other biologically active gonadal steroids and the morphological details of the ovarian follicles gleaned in the present study