Effects of dietary guava leaf aqueous extract supplementation on growth, antioxidant capacity, and non-specific immunity in mud crab <em>Scylla paramamosain</em>

Abstract

Mud crab (*Scylla paramamosain*) fed five different diets with varying concentrations of guava leaf aqueous extract (0 mg·kg^--1^, 80 mg·kg^--1^, 160 mg·kg^--1^, 320 mg·kg^--1^, and 640 mg·kg^--1^) for 30 days. Mud crabs in the 320 mg·kg^--1^ guava-leaf extract groups outperformed the control group in terms of survival rates (SR), weight gain rates (WGR), and specific growth rates (SGR). When compared to the control group, mud crabs in the 320 mg·kg^--1^ guava-leaf extract groups had significantly higher levels of lipase (LPS), pepsin, lysozyme (LZM), superoxide dismutase (SOD), acid phosphatase (ACP), and glutathione (GSH) (*P \< 0.05*). The amylase (AMS) activity was significantly decreased in all experimental groups (*P \< 0.05*). Malondialdehyde (MDA) content in the hepatopancreas of mud crabs in the 160 mg·kg^--1^, 320 mg·kg^--1^, and 640 mg·kg^--1^ guava-leaf extract groups were significantly reduced compared to the control group (*P \< 0.05*). Additionally, real-time PCR results illustrated that the expression levels of *GPx3*, *CAT*, and *JNK* were all considerably increased in the 80 mg·kg^--1^ guava-leaf extract groups compared to the control group (*P \< 0.05*). In the 160 mg·kg^--1^, 320 mg·kg^--1^, and 320 mg·kg^--1^ guava-leaf extract groups, the expression levels of *SOD* genes were considerably greater than the control (*P \< 0.05*), which was consistent with the level of SOD activity. *GST* and *P53* gene expression levels were significantly up-regulated in the 80 mg·kg^--1^, 160 mg·kg^--1^, 320 mg·kg^--1^, and 640 mg·kg^--1^ guava-leaf extract groups compared to the control group (*P \< 0.05*). Overall, the addition of 160 mg·kg^--1^-320 mg·kg^--1^ guava-leaf extract to the feed of *Scylla paramamosain* promoted growth, enhanced the activities of digestive and antioxidant enzymes, and strengthened immunity.