Effects of Phase‐Shifted Photoperiod Regimes on Oocyte Growth and Hormonal Profiles in Female Striped Bass Morone saxatilis

Abstract

Abstract.— The use of 12–mo long, but phase‐shifted advanced and delayed photoperiod cycles in the regulation of the reproductive cycle was investigated in captive‐reared female striped bass Morone saxatilis during the 3‐yr study in an attempt to control the timing of sexual maturation under simulated photoperiod conditions. Phase‐shifted photoperiod cycles did not induce a full shift in oogenesis during the first year cycles, but did in the following years. Spawning time, indicated by maximum oocyte diameters, was advanced up to 4 mo in females maintained under the phase‐shifted advanced photoperiod, and delayed up to 4 mo when they exposed to the phase‐shifted delayed photoperiod, compared to the natural spawning time in Spring (March‐May). Phase‐shifted photoperiod regimes shifted the profiles of plasma testosterone (T) and estradiol (E2), corresponding to the shift of oogenesis in the respective groups. Significant increases in T and E2 levels occurred during the vitellogenic phase, and these levels peaked before the occurrence of maximum oocyte diameters. The studies demonstrate that phase‐shifted photoperiod regimes can be used to control oogenesis, and have implications for ensuring the year‐round supply of mature female striped bass, particularly in domesticated striped bass.