Effects of a Long or an Increasing Photoperiod on the Initiation of Ovarian Recrudescence During the Preparatory Period in the Catfish, Heteropneustes fossilis (Bloch)1

Abstract

Three experiments (70-115 fish/experiment) were performed during the early-, mid-, and late-preparatory period (February to April) to study the effects of a long (21-35 fish/experiment) or a gradually increasing photoperiod (20-35 fish/experiment) on ovarian recrudescence. Normally, the ovary is completely regressed during this period. Both long (14-hr photoperiod/day) and gradually increasing photoperiods (11 or 12 to 14 hr/day) are equally effective in accelerating ovarian recrudescence. Further, the time taken for the first significant indication of ovarian recrudescence following exposure to a long photoperiod decreases with the increasing proximity of the experiment to the spawning period. In the early preparatory period, the first sign of ovarian recrudescence following exposure to a long photoperiod is seen 51 days later, whereas it takes only 33 and 23 days, respectively, if the experiment is conducted during the mid- and latepreparatory period. These data reveal that the ovary is responsive to a long photoperiod even in fish living at 28° N latitude where the photoperiod cycle changes seasonally by only 4 hr. The fourth experiment (50 fish) conducted during the preparatory period to determine the role of temperature in the photosexual response indicates that temperature plays only a facilitatory role. The significance of these findings is discussed.