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In the present study, we explored the effects of seven light treatments (white, violet, blue, cyan, green, yellow, and red) on juvenile Sinonovacula constricta (length, 693.79 ± 82.91 μm), employing dark treatment as a control. A rearing experiment was conducted for one week in which the feeding rate was examined daily, e.g., one, two and three h after feeding. At the conclusion of the experiment, overall growth was calculated, and enzymatic activity related to digestion, superoxide dismutase, catalase, and glutathione peroxidase pertaining to antioxidant biomarkers, as well as expression levels of genes related to antioxidation and stress response, were examined. The results showed that the highest growth rates were observed in the yellow light group, while the lowest growth rates were found in the violet and blue light groups; on the other hand, no significant differences were found among the other groups. Meanwhile, when exposed to white, yellow, or green light, juveniles exhibited high feeding rates, while those in the violet and blue light groups showed low feeding rates. Regarding enzymatic activity related to digestion, those of α -amylase, lipase, pepsin, and trypsin were relatively higher in the yellow light group than in the other groups. Regarding oxidative stress, the yellow light group showed higher superoxide dismutase, catalase, and glutathione peroxidase activities than the other groups. In contrast, the lowest malonaldehyde level was found in the white light group, followed by yellow light, while there were no significant differences among the other groups. In addition, the expression levels of genes related to antioxidation and stress response (heat shock protein 70 and glucose-regulated protein 78) in juveniles generally exhibited higher levels in the red light group, whereas they showed relatively lower levels in the yellow light group. Collectively, these results suggest that the application of yellow light may facilitate the growth of juvenile S. constricta , while red and violet light have opposite effects. • Light spectrum differently influenced the growth of juvenile S. constricta. • Yellow light facilitated the growth of juvenile S. constricta. • Yellow light induced less stress to S. constricta. • Red and violet lights impaired the growth of juvenile S. constricta. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to explore the optimal light intensity for the breeding of Sinonovacula constricta , and the effect of light intensity on the growth of S. constricta at different developmental stages was studied. Four developmental stages (spawning, fertilized eggs, planktonic larvae, and juveniles) and different light intensities were set up in our current experiments. The results showed that various light intensities had significantly different effects on spawning amount and initial spawning time, while it had little influence on the hatchability of fertilized eggs (P > 0.05). The spawning amount of the razor clam peaked at a light intensity of 44–250 lx (P < 0.05). In the planktonic larvae experiment, the highest survival rate appeared at 487 ± 31 lx (58.61 ± 4.0%).For juvenile S. constricta , two substratum thicknesses (1 and 5 mm) and four light intensities, including L 1 (14 ± 11 lx), L 2 (380 ± 145 lx), L 3 (3792 ± 2105 lx), and L 4 (12,244 ± 5290 lx), were set up in a 10-day experiment. When the substratum thickness of 1 mm was applied, the body length and survival rate of S. constricta juveniles (0.26 ± 0.02 mm) in the L 2 group were found to be the largest, which were significantly different compared with the other groups. When the substratum thickness was changed to 5 mm, the body length and survival rate among those groups showed no significant difference. However, when the shellfish samples were changed to a larger size of razor clam (1.45 ± 0.16 mm), a more obvious effect of light intensity on the growth was observed in a 1-mm substratum group compared with the 5-mm group. These results indicated that light intensity exerted a significant effect on the growth of S. constricta at different stages, and each stage exhibited a distinct sensitivity to light intensity. Further study from the aspects of photoreceptors and relevant genes is currently in progress in our laboratory. • Spawning, hatching and growth of S. constricta were affected by light intensity. • All developmental stages of S. constricta were photosensitive, except zygote. • Optimal light intensity is critical for S. constricta breeding and farming. [ABSTRACT FROM AUTHOR]