Effects of different photoperiod conditions on survival, growth, and gonadal development of Takifugu rubripes adults

Photoperiod has a significant influence on fish. In this study, 2.5-year-old Takifugu rubripes (tiger puffer) adults were selected to evaluate the photoperiod impacts (8 h light (L):16 h dark (D), 12L:12D, 16L:8D) from September to January at 15–17 °C on their growth, gonadal development, and survival for a 100-day. The mortality rate of males and females tiger puffer differed among the different photoperiods, and the 8L:16D photoperiod was not suitable for survival of males. At the end of the experiment, the body length, weight gain rate, specific growth rate and condition factor of both males and females tiger puffer were similar among the three photoperiods (P > 0.05). Higher percentage of females had developed to later developing phase and males had developed to spawning capable phase in the 12L:12D treatment, respectively. In particular, 100% of males had testis at the spawning capable phase. The gonadosomatic index values of males and females in the 12L:12D group were significantly higher than those in the 16L:8D group (P < 0.05), but no significant differences between the 8L:16D and 12L:12D groups (P > 0.05). The serum testosterone (T) content of males and the serum estradiol-17β (E2) content of females were highest in the 12L:12D group. The expression of aralkylamine N-acetyltransferase 1a (aanat1a) in the diencephalon/midbrain (D/M) was elevated under 12L:12D treatment in both sex (P < 0.05). The expression level of iodothyronine deiodinase type 2 (dio2) in the saccus vasculosus in males was elevated under the 12L:12D photoperiod (P < 0.05). The levels of gonadotropin-releasing hormone 1 (gnrh1) and gnrh3 mRNA in the D/M of females at later developing stages in the 12L:12D treatment were significantly higher than those in of other treatment groups, and the level of gnrh3 in males under this photoperiod was significantly elevated (P < 0.05). The levels of gonadotropin-inhibiting hormone (gnih) mRNA under 12L:12D were significantly elevated in both males and females (P < 0.05). Under this photoperiod, the levels of follicle stimulating hormone b-subunit (fshb) and luteinizing hormone b-subunit (lhb) in the pituitary gland of females at later developing stages were significantly higher than those of the other two groups (P < 0.05). The expression levels of lhb in males in the 12L:12D and 8L:16D photoperiods were significantly higher than that at 16L:8D (P < 0.05). These results indicated that culture under the 12L:12D photoperiod from September prior to the spawning season could result in accelerated gonadal development of both male and female tiger puffer.