Effects of β-glucan combined with the gut probiotic Klebsiella sp. E26 on growth, energy metabolism, and immune response in pacific white shrimp (Penaeus vannamei) under low salinity stress

Low-salinity aquaculture is an important direction for the sustainable development of Pacific white shrimp (Penaeus vannamei). However, prolonged low-salinity rearing can have various negative impacts on shrimp health. Therefore, identifying effective strategies to alleviate the adverse effects of low-salinity stress is crucial for increasing the efficiency and sustainability of shrimp farming. This study acclimated P. vannamei to 3 salinity by adding 0.1 % β-glucan, and isolated and identified a potential probiotic strain, Klebsiella sp. E26, with enzyme production, antibacterial activity, and high safety. Subsequently, an 8-week in vivo experiment was conducted to evaluate the synergistic effect of β-glucan and Klebsiella sp. E26 (synbiotics) on the growth, energy metabolism, and immune response of P. vannamei under low-salinity stress. Four groups were set up: a control group (basal diet), a prebiotic group (0.1 % β-glucan), a probiotic group (10⁹ CFU/g Klebsiella sp. E26), and a synbiotic group (0.1 % β-glucan and 10⁹ CFU/g Klebsiella sp. E26). All groups were fed under 3 salinity conditions. The results indicated that the synbiotic consisting of β-glucan and Klebsiella sp. E26 significantly enhanced the overall immune capacity of shrimp by activating energy metabolism pathways and immune pathways in the hepatopancreas. Specifically, Klebsiella sp. E26 promoted the metabolism of short-chain fatty acids, increasing the energy supply under low-salinity stress and maintaining this effect in the synbiotic group. Additionally, synbiotic treatment improved the composition of the gut microbiota, reduced the need for high metabolic activity in the gut, and thus decreased sensitivity to low-salinity stress. Overall, synbiotic treatment with β-glucan and Klebsiella sp. E26 significantly enhanced the adaptation of shrimp to low-salinity stress by optimizing the gut microbiota, promoting the expression of immune-related genes, and activating energy metabolism pathways. This study not only elucidates the synergistic mechanism of β-glucan and probiotics under low-salinity conditions but also provides a novel strategy for mitigating the adverse effects of low-salinity stress in P. vannamei.