Light plays a critical role in the physiology and pigmentation of aquatic animals. Regulating the light environment of aquatic animals offers insights into healthy aquaculture practices. In this study, Procambarus clarkii were reared under four different light colors—white (WL), red (RL), blue (BL), and green (GL)—for 21 days, with four replicates per light color. Morphological characteristics did not differ among light treatments. However, significant differences were observed in hemolymph cortisol levels and tyrosinase activity across different tissues (hemolymph, muscle, hepatopancreas) among groups (RL > BL > GL > WL). Hepatopancreatic CAT activity in WL was significantly higher than that in GL and BL, whereas hepatopancreatic MDA content was highest in BL. Regarding chromatic parameters, the yellow color of the RL cephalothorax cuticle and the red color of the muscle were more pronounced than in WL, The chela cuticle of GL is darker than RL, while the red color of the chela cuticle was more pronounced than in WL.. For pigment content, cephalothorax cuticle astaxanthin content in BL was significantly higher than that in other light color groups, while abdominal cuticle astaxanthin content was lowest in BL. Chela cuticle astaxanthin content in RL was significantly higher than that in WL, and chela cuticle astaxanthin and lutein contents in WL were significantly lower than those in BL and GL. Compared with WL, hepatopancreatic glutathione S-transferase P1 (GSTP1) mRNA expression significantly decreased under colored light, whereas NinaB mRNA expression significantly increased under RL and BL. These results indicate that light color does not affect the morphological characteristics of P. clarkii but significantly modulates oxidative stress responses, physiological status and energy metabolism. Different light colors may mediate carotenoid transport and deposition by regulating the expression of GSTP1, NinaB, leading to specific chromatic differences in different body parts of P. clarkii. Comprehensive analysis revealed that the red light environment exerted a more positive effect on enhancing the body color of P. clarkii. This study provides a reference for revealing the mechanism of light color regulating crustacean physiological function and pigmentation and optimizing aquaculture model.

Crayfish with cyan soft-carapace and red hard-carapace differ considerably in market value. To investigate the causes underlying this difference in shell color, we selected 120 healthy Procambarus clarkii of similar size (9–10 cm), equally divided by shell color and sex. Muscle quality, pigment deposition, and DGAT2 mRNA expression were compared between the two shell-color types. The results showed that: (1) Muscle hardness was significantly higher in red hard-carapace crayfish than in cyan soft-carapace crayfish (p < 0.05), whereas no significant difference in muscle elasticity was observed among groups (p > 0.05). (2) A significant interaction between shell color and sex influenced crude fat and ash content (p < 0.05). Crude fat content was higher in red hard-carapace crayfish, and ash content was highest in male red hard-carapace crayfish, significantly exceeding that in male cyan soft-carapace crayfish (p < 0.05). (3) Moisture and crude protein content were not significantly affected by the interaction between shell color and sex (p > 0.05), with no notable differences across groups. (4) The contents of astaxanthin, lutein, and β-carotene in the shell were significantly influenced by the interaction between sex and shell color (p < 0.05). Astaxanthin was lowest in female cyan soft-carapace crayfish, and lutein was highest in male red hard-carapace crayfish, and β-carotene showed no significant differences. (5) DGAT2 mRNA expression was highest in hepatic tissue across all groups (p < 0.05). In gonads, expression was higher in ovaries of cyan soft-carapace crayfish and in testes of red hard-carapace crayfish (p < 0.05). (6) DGAT2 mRNA expression in the inner membrane, muscle, and intestine was significantly affected by the interaction between shell color and sex (p < 0.05), with specific expression patterns varying among tissues and groups. These findings indicate that shell color and sex interact to influence nutritional composition, carotenoid profile, and gene expression, providing insights into the mechanisms of body color formation and its physiological correlates.