Photothermal control of the reproductive cycle in temperate fishes

Temperate fish species are annual spawners and mainly rely on annually cycling cues (temperature and photoperiod) to synchronise the three main phases of their reproductive cycle, that is, induction (initiation of oogenesis), vitellogenesis and the final stages (including maturation, ovulation and oviposition). This review synthesises how these three phases are controlled by specific temperature and photoperiod variations. The direction of the changes (i.e. decrease or increase) is the most important factor, although the amplitude, rates and timing of variations should also be considered to improve/optimise the quality of reproduction in aquaculture. In addition, we tentatively classified temperate fish species sharing similar temperature and/or photoperiod variation requirements for reproduction into three general functional groups. The first group (salmonids) is induced by increasing photoperiod. Vitellogenesis and the final stages are synchronised by decreasing photoperiod. The second group (percids, moronids and gadids) is induced by decreasing both temperature and photoperiod. A chilling period allows vitellogenesis. Increasing temperatures synchronise the final stages. The third group (cyprinids) is induced by decreasing either photoperiod or temperature. Vitellogenesis is faster at warm temperatures. The final stages require an increase in either photoperiod or temperature. This classification may help future research on the control of reproduction in newly cultured fish species.