Photoperiod and Temperature Control in the Regulation of Reproduction in the Female Catfish Heteropneustes fossilis

Abstract

The annual reproductive cycle of the catfish Heteropneustes fossilis is divided into the preparatory period (February–April), prespawning period (May–June), spawning period (July–August), and postspawning period (September–January). Ovarian recrudescence, which normally occurs during the prespawning period, can be advanced by photothermal manipulations. During the postspawning and preparatory periods, the tempo of ovarian recrudescence is much faster at 30 C than at other temperatures (ambient, 25 or 34 C) regardless of photoperiod (14L + 10D, 12L + 12D, or 9L + 15D).Warm temperature (30 C) postpones the postspawning ovarian regression only up to the first week of October regardless of photoperiod. The ovarian cycle is regulated by a circannual rhythm which can be activated 5 mo earlier, but its activity cannot be prolonged beyond October by photoperiodic and temperature manipulations.Interruption of the night of a short day (6L + 18D) treatment by 1 h of light between 0000 and 0100 induces ovarian recrudescence that is significantly greater than that obtained in the control group exposed to 7L + 17D. Scanning of the major part of the dark period (1800–0500) to determine the duration of the photo-inducible phase shows that it lies between 0000 and 0500 with peaks from 0000 to 0100 and from 0400 to 0500. Even 1 h of light in a regimen of 1L + 23D presented between 1900 and 0500 produces significant ovarian recrudescence with peaks between 2200 and 0100. These results clearly demonstrate the possible involvement of a circadian mechanism for photoperiod measurement in the catfish.Precociously gravid catfish obtained as early as April by photothermal treatment have been induced to spawn in the laboratory by administration of ovine luteinizing hormone (LH). Ripe eggs after fertilization hatched into seemingly normal fry. Further, the spent fish when subjected to the same photothermal treatment developed a fresh crop of yolky eggs within 1 mo; such gravid females have been again induced to spawn with LH. This process has been repeated so that the same set of fish have been spawned 4 times between April and July of the same year. Thus, it is possible to get catfish fry not only early but also 2.6 times more than that usually available from each female during the spawning season. The aquacultural potentialities of this laboratory discovery are discussed.