EFFECTS OF TEMPERATURE AND LIGHT ON THE CYCLICAL CHANGES IN THE SPERMATOGENETIC ACTIVITY OF THE LAKE CHUB, COUESIUS PLUMBEUS (AGASSIZ)

Abstract

Lake chub obtained from their natural habitat, at three different periods of their annual reproductive cycle, were subjected to four combinations of photoperiod and temperature. Temperature is the major environmental factor controlling spermatogenesis. Higher temperatures (16–21 °C) promote prespermatocytal changes (proliferation of spermatogonia) and hasten or terminate spermiation in prespawning fish; low temperatures (5–12 °C) are essential for normal gonadal proliferation and formation of the primary spermatocytes. Temperature effects are not overridden by either of the two contrasting photoperiods, but at lower temperatures a definite, although slight, photoperiodic effect is evident in the terminal part of all three experiments, Photoperiod does not appear to dominate spermatogenetic processes at any stage. Evidence is presented that an endogenous rhythm of activity is also present and may be partly responsible for the timing of the various testicular changes.