The body color of aquatic products is a key indicator that aquaculture practitioners use to evaluate health status and consumers use to judge quality. Carotenoids are natural pigments that are mainly pigmented compounds responsible for red, yellow, and orange coloration. They have important functions, such as immune and antioxidant modulation. Recently, a novel strain of Pelodiscus sinensis with bright yellow color, named the Yongzhang golden turtle (YGT), was obtained through selective breeding. However, the actions of carotenoids on its coloration, antioxidant activities and immune competence have not been investigated yet. In this study, we examined the concentration of carotenoids in the skin and calipash of the atrovirens wild-type turtle (AWT) and YGT by spectrophotometry and found that the concentration of carotenoids in the YGT was significantly higher than that in the AWT. Then, we measured relevant antioxidant activity indicators, including total antioxidant capacity (T-AOC) and malondialdehyde (MDA), by commercial kits in the YGT and AWT, identifying higher activities of T-AOC in the YGT compared with those in the AWT, while MDA contents were decreased in the YGT compared to those in the AWT. We quantified the immune competence of the YGT and AWT using plasma bacteria-killing ability (BKA) and immunoglobulin M (IgM) expression. Compared to plasma from the AWT, that of the YGT showed higher antibacterial activity against Escherichia coli, Aeromonas hydrophila, Staphylococcus aureus, Salmonella typhimurium, and Citrobacter freundii. However, there was no difference in IgM expression between the YGT and AWT. Correlation analysis suggested that carotenoids concentration were positively associated with T-AOC and BKA, and negatively associated with MDA. In conclusion, the bright yellow color of YGT was mainly caused by carotenoids, which could enhance the antioxidant capacity and immune competence. Therefore, the YGT, with yellow coloration, possesses a high ornamental value and is much better in quality than the AWT.

水产品的体色是水产养殖从业者用来评价健康状况和消费者用来判断质量的关键指标。类胡萝卜素是天然色素，主要是负责红色、黄色和橙色着色的色素化合物。它们具有重要的功能，例如免疫和抗氧化调节。最近，一种新的中华鳖经选育得到黄色亮黄色鳖，命名为永章金龟（YGT）。然而，尚未研究类胡萝卜素对其着色、抗氧化活性和免疫能力的作用。在这项研究中，我们通过分光光度法检测了 atrovirens 野生型龟 (AWT) 和 YGT 的皮肤和鳖中类胡萝卜素的浓度，发现 YGT 中的类胡萝卜素浓度明显高于 AWT。然后，我们通过 YGT 和 AWT 中的商业试剂盒测量了相关的抗氧化活性指标，包括总抗氧化能力（T-AOC）和丙二醛（MDA），与 AWT 相比，YGT 中的 T-AOC 活性更高，与 AWT 相比，YGT 中 MDA 含量降低。我们使用血浆杀菌能力 (BKA) 和免疫球蛋白 M (IgM) 表达量化了 YGT 和 AWT 的免疫能力。与来自 AWT 的血浆相比，YGT 的血浆显示出更高的抗菌活性大肠杆菌、嗜水气单胞菌、金黄色葡萄球菌、鼠伤寒沙门氏菌和弗氏柠檬酸杆菌。然而，YGT 和 AWT 之间的 IgM 表达没有差异。相关分析表明，类胡萝卜素浓度与T-AOC和BKA呈正相关，与MDA呈负相关。总之，YGT的亮黄色主要是由类胡萝卜素引起的，可以增强抗氧化能力和免疫能力。因此，黄色的YGT具有很高的观赏价值，质量比AWT好得多。