Effects of different light conditions on growth, muscle nutrients content, and clock gene circadian expression of Takifugu rubripes

Basic knowledge about the effect of light on fish in needed to improve their development, survival, and growth to increase aquaculture efficiency. In this study, the effects of light photoperiods (light (L): dark (D) = 12:12 and 16:8) and spectrum (full spectrum (W), blue (B) and yellow (Y)) on Takifugu rubripes larvaes were assessed from 20 to 80 days after hatching (dah). At 50 dah, the body length of larvae exposed to Y16:8 and B16:8 was significantly higher than that in the W16:8 group (P < 0.05). The wet weight of larvae reared under B16:8 was significantly higher than that under B12:12 (P < 0.05). The wet weight of larvae exposed to B12:12 was significantly higher than that in the W12:12, and the wet weight of larvae exposed to B16:8 was significantly higher than that of larvae exposed to W16:8 and Y16:8 (P < 0.05). At 80 dah, the body length and wet weight of larvae reared under 12:12 were significantly higher than those of larvae reared under 16:8 in the white and yellow LEDs groups (P < 0.05). Additionally, the biochemical composition of muscle were affected, the levels of DHA and EPA+DHA were significantly higher in the W16:8 and B16:8 groups, compared to the W12:12 and B12:12 groups, respectively (P < 0.05). Since light is the predominant signal for the entrainment of circadian oscillators and controls growth as a zeitgeber, the expression of arylalkylamine N-acetyltransferase 2 (annat2), crytochrome 2 (cry2), peroid1 (per1) and per3 in the brain were also been measured. The long photoperiod 16:8 delayed the acrophases of annat2, and blue light decreased the expression of cry2 and per3. These results provide the theoretical basis for using LED lights in aquaculture production of T. rubripes larvae.