Postbiotics from Saccharomyces cerevisiae fermentation protect the Chinese mitten crab (Eriocheir sinensis) against hypoxia-thermal stress through metabolic regulation and antioxidant defense

This study investigated the protective mechanisms of postbiotics from the Saccharomyces cerevisiae fermentation product (SCFP) against combined hypoxia-thermal stress in Chinese mitten crabs. Juvenile crabs were randomly allocated into four treatment groups (n = 4 tanks/group, 40 crabs/tank) and fed diets with 0 g/kg SCFP (control and nonsupplemented stress groups), 3.2, or 6.4 g/kg SCFP for 56 days. SCFP supplementation significantly increased weight gain compared with the control group (p < 0.05). Following the feeding trial, the control group remained under optimal conditions (24 °C, 7.0 mg/L dissolved oxygen), whereas the three stress groups (0, 3.2, and 6.4 g/kg SCFP) were exposed to acute hypoxia-thermal stress (30 °C, 1.0 mg/L dissolved oxygen, 24 h). Under stress conditions, oxygen consumption rates were significantly elevated in nonsupplemented crabs, whereas SCFP supplementation maintained rates comparable to those of the control (p < 0.05). Integrated transcriptomic and WGCNA analyses revealed that hypoxia-thermal stress significantly upregulated stress response pathways while suppressing energy metabolism pathways. SCFP supplementation modulated key metabolic pathways, particularly oxidative phosphorylation and amino acid metabolism. Biochemical and cellular analyses confirmed that 6.4 g/kg SCFP restored the NADPH-dependent redox balance and maintained integrity of the mitochondrial membrane potential, effectively counteracting stress-related metabolic imbalances. This improved metabolic state was supported by enhanced antioxidant capacity. Specifically, SCFP supplementation reduced cellular reactive oxygen species levels, decreased malondialdehyde content (p < 0.05), and improved glutathione/oxidized glutathione ratio. These findings demonstrate that SCFP supplementation protects crabs against hypoxia-thermal stress through integrated metabolic and antioxidant mechanisms, offering a promising nutritional strategy for intensive aquaculture.