Effects of Dietary Copper on Growth Performance, Antioxidant Capacity, Muscle Quality and the Expression of Copper-Transport and Muscle Development-Related Genes in Juvenile Red Swamp Crayfish (Procambarus clarkii)

This study assessed the influence of different dietary Cu2+ concentrations (1.48, 12.72, 27.71, 65.09, and 121.34 mg/kg) on the growth and physiology of juvenile crayfish (1.84 ± 0.01 g) during an 8-week feeding trial. A total of 500 crayfish were randomly allocated to the five dietary treatments, with four replicate cement ponds per treatment and 25 crayfish per tank. Growth performance was optimal in the 27.71 mg/kg group; relative to the 1.48 mg/kg group, weight gain rate (WGR) increased by 18.6% (from 749.74 ± 3.58% to 889.54 ± 9.18%), specific growth rate (SGR) by 7.3% (from 3.82 ± 0.01 to 4.10 ± 0.02%/d), and feed conversion ratio (FCR) decreased by 21.3% (from 1.69 ± 0.03 to 1.33 ± 0.02) (p < 0.05). Cu2+ deposition in muscle, hemolymph and hepatopancreas increased with dietary Cu2+ concentrations, accompanied by elevated transcriptional levels of copper-transporting ATPase 7 (ATP7) and a peak in copper transporter 1 (Ctr1) in the 27.71 mg/kg group. Phenoloxidase (PO) concentration and copper/zinc superoxide dismutase (Cu/Zn-SOD) activity in hemolymph peaked in the group of 27.71 mg/kg Cu2+, whereas malondialdehyde (MDA) concentrations reached their lowest. Excessive Cu2+ (121.34 mg/kg) induced oxidative stress and suppressed growth performance. 27.71 mg/kg Cu2+ significantly increased the hardness, gumminess and shear force of crayfish muscle compared with the other groups (p < 0.05). Meanwhile, this Cu2+ concentration increased muscle fiber diameter, an effect that was accompanied by lower myostatin (MSTN) and higher myosin heavy chain (MyHC) transcript levels in muscle. Additionally, 27.71 mg/kg Cu2+ significantly increased hydroxyproline (HYP) content (p < 0.05). Based on WGR and FCR, a segmented linear regression analysis was conducted, estimating the optimal dietary Cu2+ requirements for juvenile P. clarkii to be 28.57 and 31.50 mg/kg, respectively. These findings provide novel insights into Cu2+-regulated growth and muscle quality in crayfish aquaculture.