Atlantic salmon are increasing being reared on-land to larger sizes, but this is associated with an increased risk of unwanted sexual maturation. This is especially true of post-smolt maturation, a phenotype not typically observed in wild salmon. The environment plays a significant role in regulating the timing of maturation in salmon, especially temperature and photoperiod. Here, we present data from two experiments exploring the use of constant temperatures and photoperiods, methods often used in land-based facilities. In the first, we reared 200g post-smolts in seawater at one of eight temperatures ranging from 3 to 20.5°C (in increments of 2.5°C) on constant light for 140 days. The occurrence of pubertal fish was lower in females compared to males, but both increased with rearing temperature (Figure 1A). Female puberty was evident at 13.0°C and above, while male puberty was evident from 5.5°C and above. At the end of the trial, there was 75 and 100% female and male puberty, respectively, at 20.5°C. This was not associated with growth rate, as the quickest growth was found in those reared at 10.5°C. In the second experiment, 120g salmon in freshwater were exposed to a square wave (long-short-long) photoperiod to trigger smoltification (seawater adaptation). After the period of short daylength, salmon were exposed to 16°C and one of three “long” photoperiods; constant light (24:0 light/dark), 21:3, or 18:6. The idea being to see if a short scotophase could be used to impede maturation. Indicators of puberty were assessed for six weeks. At the end of the trial, the total prevalence of male puberty was 33, 10, and 12% in the 24:0, 21:3 and 18:6 treatments, respectively (Figure 1B), whereas no females showed any signs of sexual maturation. Again, the prevalence of puberty was not associated with growth rate in the different photoperiods. In conclusion, both temperature and photoperiod have a regulatory effect on the prevalence of post-smolt maturation. As such, salmon producers are advised to use lower rearing temperatures (e.g. ≤8°C) and avoid the use of constant light when rearing fish over 100g.