Effects of Carbon Source Addition on Growth and Immunity of Litopenaeus vannamei Based on Saline–Alkali Water Culture Environment

With the intensifying global freshwater shortage, the efficient utilization of saline-alkaline water has become a critical research focus in aquaculture. This study investigated the effects of regulating the carbon-to-nitrogen ratio (C/N = 15) in saline-alkaline water by addition of brown sugar, corn straw powder, and peanut shell powder, on the culture environment and health of Litopenaeus vannamei. The brown sugar group (HT) significantly improved water quality, with total ammonia nitrogen (TAN) maintained at ≤4.5 mg/L and nitrite (NO2−) at ≤ 2 mg/L— a 41.6% reduction compared to the control group (TAN peak value of 7.70 mg/L). Rapid biofloc formation in the HT group also alleviated high alkalinity stress (pH 8.57 ± 0.34 and control 8.94 ± 0.35). Relative abundance of Bacillus in HT group increased to 18.7% (6.3% in control), whereas proportion of Vibrio decreased, indicating that carbon source type directly influenced probiotic proliferation and pathogen suppression. The HT group exhibited the best growth performance, with a final body weight of 8.31 ± 0.25 g, a specific growth rate (SGR) of 5.48 ± 0.15%·d-1, and a survival rate of 96%, all of which were significantly higher than those in other treatments. Furthermore, hepatopancreatic antioxidant enzyme activities, including superoxide dismutase and catalase, reached 129.67 U/mg prot and 22.33 U/mg prot, respectively, increases of 26.7% and 29% over the control group. These findings confirm that carbon supplementation mitigates oxidative stress by enhancing antioxidant capacity. Brown sugar was identified as an efficient carbon source for L. vannamei culture in saline-alkaline water systems. This study provides essential theoretical support for carbon source selection and biofloc technology optimization in saline-alkaline water aquaculture.