The effects of photothermal manipulation on reproductive development in female haddock Melanogrammus aeglefinus L.

Haddock (Melanogrammus aeglefinus L.) were maintained on either simulated natural (SNP) or advanced, phase‐shifted photoperiods (ADV) and reproductive characteristics of female fish were measured throughout two reproductive cycles. By advancing the seasonal photoperiod 8 weeks, relative to ambient conditions, follicle development, peak levels of estradiol and initiation of spawning were all accelerated compared with fish maintained on an SNP. Profiles of steroid synthesis and follicular development were similar between the two groups but the spawning period was protracted by 40 days in the fish maintained on ADV. Ultrasound imaging proved to be an effective and non‐invasive tool for accurately assessing ovarian development throughout the reproductive cycle. These results suggest that photoperiod manipulation has significant potential for extending the availability of eggs and larvae for haddock aquaculture.