Dietary yeast culture can protect against chronic heat stress by improving the survival, antioxidant capacity, immune response, and gut health of juvenile Chinese mitten crab (Eriocheir sinensis)

As global warming intensifies, aquatic species are increasingly threatened by heat stress, urging the aquaculture industry to explore innovative strategies to mitigate the adverse impact of thermal stress on animals. Supplementing diets with yeast culture (YC) has shown promising results in coping with heat stress. This study evaluated the effects of YC on the survival, biochemical responses, transcriptome, and intestinal microbiota of the Chinese mitten crab (Eriocheir sinensis) under chronic heat stress. Juvenile crabs were subjected to four conditions over 42 days: a control temperature of 24 °C and a high temperature of 30 °C supplemented with three YC doses: 0, 3.2, and 6.4 g/kg. Each group had six replicates of 30 crabs each. Chronic heat stress substantially reduced survival rates and increased molting frequency. However, YC supplementation significantly improved survival and antioxidant enzyme activities (SOD and GSH-Px) while reducing MDA levels, indicating a reduction in oxidative stress. The immune response metrics (PO and AKP activities) were comparable to those of the control group when YC was included in the diet. A significant correlation existed between the crab survival rate, antioxidant performance and gut health. Histological assessment revealed that YC maintained the integrity of the intestinal lining under heat stress. 16S rRNA sequencing revealed that YC ameliorated disruptions in the diversity and structure of the intestinal microbiota caused by high temperature. Transcriptomic analysis identified DEGs linked to serine-type peptidases and ascorbate and aldarate metabolism pathways. Significant correlations were detected between Candidatus_Hepatoplasma, Rhodobacter, Aeromonas, and genes related to antioxidant and immune responses. In conclusion, dietary YC at 3.2 g/kg effectively enhanced the resilience of E. sinensis to chronic heat stress by increasing survival rates and antioxidant capacity, restoring immune function, and maintaining gut health.