Effects of Light Color on the Growth, Feeding, Digestion, and Antioxidant Enzymes of <i>Tripneustes gratilla</i> (Linnaeus, 1758)

To study the effects of light color on sea urchin (<i>Tripneustes gratilla</i>), blue light (B, λ_450nm), yellow light (Y, λ_585–590nm), red light (R, λ_640nm), green light (G, λ_510nm), white light (W, λ_400–780nm), and darkness (H) groups were established in a recirculating seawater aquaculture system. Six different LED light color treatment groups with a photoperiod of 12 L:12 D were tested for 30 days to investigate the effects of different light colors on the feeding, growth, and enzyme activities of <i>T. gratilla</i> (142.45 ± 4.36 g). We found that using different LED light colors caused significantly different impacts on the feeding, growth, and enzyme activity of <i>T. gratilla</i>. Notably, the sea urchins in group B exhibited better growth, with a weight gain rate of 39.26%, while those in group R demonstrated poorer growth, with a weight gain rate of only 26%. The feeding status differed significantly (<i>p</i> < 0.05) between groups B and R, with group B consuming the highest daily intake (6.03 ± 1.69 g) and group R consuming the lowest (4.54 ± 1.26 g). Throughout the three phases, there was no significant change in the viability of the α-amylase (<i>p</i> > 0.05). Conversely, the pepsin viability significantly increased (<i>p</i> < 0.05) in group B. The lipase viability consistently remained at the lowest level, with no notable differences between group W and group B. In group R, both the α-amylase and pepsin viabilities remained lower, whereas the lipase viability was noticeably greater in each phase than in group B (<i>p</i> < 0.05). Among the antioxidant enzymes, group R exhibited a trend of initial increase followed by decreases in catalase, superoxide dismutase, and glutathione peroxidase activities, particularly during the third stage (15–30 days), during which a significant decrease in antioxidant enzyme activity was observed (<i>p</i> < 0.05). Taken together, these findings suggest that blue light positively affects the growth, feeding, digestion, and antioxidant capacity of <i>T. gratilla</i> in comparison with those in other light environments, whereas red light had an inhibitory effect. Furthermore, <i>T. gratilla</i> is a benthic organism that lives on shallow sandy sea beds. Thus, as short wavelengths of blue and green light are more widely distributed on the seafloor, and long wavelengths of red light are more severely attenuated on the seafloor, shorter wavelengths of light promote the growth of bait organisms of sea urchins, which provide better habitats for <i>T. gratilla</i>.