Responses of the Pituitary and Ovary of the Catfish, Heteropneustes fossilis (Bloch) to Accelerated Light Regimen of a Decreasing Followed by an Increasing Photoperiod During the Postspawning Period1

Abstract

Three experiments (80–98 fish/experiment) conducted during the postspawning period show that the ovaries of the catfish respond to an increasing photoperiod only if they have had prior exposure to a decreasing photoperiod. The first sign of ovarian recrudescence is seen when the photoperiod increases from 12 to 14 hours/day indicating that the catfish may be attuned to recognize the changes in day length that follow the vernal equinox. The pituitary gland is an important link in the photosexual response. In the control catfish, the pituitary has very few PAS-positive basophils in the proximal pars distalis (PPD) and this does not change during the course of the experiment; whereas, in the catfish subjected to an accelerated light regimen of a decreasing followed by an increasing photoperiod, an increase in the number and size of the basophils in the PPD is noticed contemporaneous with the appearance of stage II and stage III occytes in the ovary. Presumably, prior exposure to a decreasing photoperiod abolishes the refractoriness, so much so, the hypothalamo–hypophyseal–ovarian system responds to an increasing photoperiod. The significance of these results is discussed.