Effects of copper supplement on the immune function and blood-chemistry in adult Chinese horseshoe crab Tachypleus tridentatus

Oxygen in hemocyanin binds to copper ions and turns the hemolymph of horseshoe crabs blue. Copper ions not only transport oxygen but also enhance the immune function of horseshoe crabs. A 28-day indoor culture experiment was conducted to study the effects of adding different levels of copper amino acid chelate (0, 50, or 100 mg kg−1) into semi-finished feed on the nonspecific immune enzyme activity and hemolymph biochemical parameters of Tachypleus tridentatus. Results revealed that the activities of serum antioxidant enzyme indicators, namely, copper–zinc superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione peroxidase (GPX), total antioxidant capacity (T-AOC), lysozyme (LZM), alkaline phosphatase (AKP), and acid phosphatase (ACP), of copper-fed adult horseshoe crabs increased; on the other hand, malondialdehyde (MDA) activity decreased. Hemolymph biochemical indicators, triglyceride (TG) and cholesterol (CHO) decreased in the copper-fed group, but hemocyanin concentration (HC) levels increased during the experiment. At the end of experiment, all antioxidant enzymes and blood biochemical indicators in the copper-fed group were significantly different from those without copper supplement. Hemolymph T-AOC, MDA, AKP, ACP values in the low-level copper group (50 mg kg−1) were significantly different from those in the high-level copper group (100 mg kg−1).