Effects of advanced and continuous photoperiod regimes on maturation control and profiles of sex steroids in brook trout (Salvelinus fontinalis)

Maturation of salmonid species reduces growth, flesh quality and immunocompetency and has inhibited, in part, the commercial production of brook trout in Tasmania. Photoperiod manipulation is routinely used to inhibit or reduce the incidence of maturation in salmonids, so an experimental adaptation of this approach was trialled experimentally for brook trout. Mixed-sex fish (age = 14 months) were subjected to simulated natural photoperiod (NP), advanced photoperiod (AP) and continuous photoperiod (CP) to investigate the response of endogenous circannual rhythm upon sexual maturity in this species. Light treatments commenced on the first day of the last month of the southern hemisphere’s winter and concluded towards the end of autumn when fish were ovulating. Maturation was observed in 100% of females and 96% of males held under NP. Fish exposed to AP corrected their maturation cycle by advanced phase shift of their endogenous rhythm for eight weeks and achieved final maturation during March–April. Plasma profiles of testosterone and oestradiol-17β were also adjusted according to advancement of photoperiod. Exposure to AP inhibited maturation by 6% and 8% in males and females, respectively. CP treatment for 10 consecutive months failed to inhibit gonadal development; however, this regime did delay or inhibit spermiation and ovulation.