Effects of Light Spectrum on Growth, Retinal Morphology, and Clock Gene Expression Patterns in Takifugu rubripes Larvae

Light exhibits a significant influence on aquatic organisms. This study assessed the effects of five light spectra (blue, red, green, yellow, and full-spectrum white) on the growth and survival of Takifugu rubripes larvae. The results showed that the wet weight, body length, and specific growth rate (SGR) of fugu larvae in the green and yellow light spectra groups were significantly better than those in the other groups. The qPCR results showed that growth hormone (gh) expression was significantly higher in larvae from the yellow light spectrum group. There was a significant increase in mRNA expression of trypsinogen in the yellow light spectrum group and pepsinogen in the green light spectrum group compared with the other groups, indicating that light regimes may help regulate endocrine function and digestive efficiency. The blue light spectrum significantly decreased the thickness of the photoreceptor layer (PRos/is), accompanied by increased expression of the apoptosis marker caspase3, which may be related to decreased expression of melanin-concentrating hormone receptors (mchr1/2). Analysis of clock genes (such as per3, per1a, and cry2) revealed disrupted expression patterns under blue light, particularly at Zeitgeber time 12 (lights-off), indicating interference with circadian regulation. Our study indicated that optimizing lighting by prioritizing the green or yellow light spectrum can enhance growth efficiency and minimizing prolonged exposure to blue light is essential for retinal health during T. rubripes aquaculture.