Constant High Temperature Promotes Early Changes in Testis Development Associated with Sexual Maturation in Male Atlantic Salmon (Salmo salar L.) Post-Smolts

Sexual maturation of post-smolts is a concern for Atlantic salmon producers, and its occurrence dependent upon factors such as water temperature energy availability, among others. The present study was designed to investigate the effect different temperatures feeding regimes on testis development local regulation spermatogenesis in post-smolts. A 3 × 2 factorial design used, with three (8 °C, 12.5 18 °C) two feed (100% 67% ration). Salmon (1800 parr, initial mean weight 23.1 ± 7.2 g) were reared from 28 October 2018 30 May 2019 freshwater flow-through system under continuous light (LD24:0), except 5-week winter signal (LD12:12) introduced 4 February 2019. Testis histology, transcription follicle-stimulating hormone receptor (fshr) luteinizing (lhr), proteins involved gonadal-soma-derived 1 (gsdf1) (gsdf2), anti-Müllerian (amh), insulin-like growth factor-3 (igf3), analyzed. Results showed that high alone (18 °C), irrespective regime, promoted early presence type B spermatogonia reduced transcript levels proliferation-inhibitory factor amh males still considered immature, groups 18–100% 18–67% later matured proportion (~100%). This also some degree group 12.5–100% (40% maturation), absent 12.5–67%, 8–100%, 8–67% (groups little or no maturation). Later, at onset rapid growth, linked pronounced downregulation self-renewal gsdf1 gsdf2, well upregulation proliferation-stimulating igf3. Overall, findings demonstrate rearing can stimulate an activation brain–pituitary–gonad axis before actual enhancing accelerating mechanisms control initiation progression maturation, while regime has minor impact. poses challenge current aquaculture practices use sustained maximize since these increase risk post-smolt maturation.