title: Responses of the regressed ovary of the catfish, Heteropneustes fossils (Bloch), to interrupted-night photoperiods.
abstract: Interrupted-night photoperiod schedules were used to explore the possibility of the involvement of a ciradian rhythm in photosensitivity in ovarian recrudescence in the catfish, Heteropneustes fossilis. Interruption of the night of a basic short day (L/D 6:18) treatment by 1-h of light between 00(00) and 01(00) induced ovarian recrudescence which was significantly higher than that in the control group exposed to L/D 7:17. Scanning of the major part of the dark period (20(00-05(00)) to determine the duration of the photo-inducible phase shows that the photo-inducible phase lies between 20(00) and 03(00) with a peak from 00(00) to 01(00). Even 1-h of light in a regimen of L/D 1:23 presented between 20(00)-21(00), 22(00)-23(00), 00(00)-01(00), 02(00)-03(00), or 04(00)-05(00), produced significant ovarian recrudescence with a peak between 22(00) and 23(00). These results provide a clear demonstration of the possible involvement of a circadian mechanism for photoperiod measurement in the catfish.
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D005399:Fishes / Q000502:physiology*; D009929:Organ Size; D010053:Ovary / Q000254:growth & development*