Synergistic effects of biofloc and astaxanthin on pigmentation, immunity, and intestinal microbiota of Litopenaeus vannamei

The impact of dietary astaxanthin (AST) levels on the growth performance, pigment deposition, immune function, and gut microbiota of Litopenaeus vannamei reared under biofloc technology (BFT) and clear-water systems was systematically investigated in this work to evaluate the potential synergistic effects between BFT and dietary AST. Along these lines, shrimps with an initial body weight of 3.94 ± 1.58 g were fed diets supplemented with 0, 60, 80, 100, or 120 mg/kg AST and cultured for 35 days under either BFT or clear-water conditions. From our analysis, it was demonstrated that: (1) the interaction between the culture mode and AST level (Model × AST) significantly affected shrimp’s survival rate and weight gain rate (WGR) ( P < 0.05). A quadratic regression model based on WGR was applied, yielding a theoretical optimum AST level of 91.77 mg/kg under BFT conditions; (2) the deposition of AST in tissues was affected by both culture mode and dietary AST level; however, a significant interaction between these factors was detected only for the AST content in the uropod ( P < 0.05); (3) various body colour parameters, immune enzyme activities, and antioxidant capacity all exhibited significant interactive enhancement effects ( P < 0.05), with the B80 group showing the best overall performance;and (4) gut microbiota analysis indicated that BFT and AST jointly altered the composition and predicted functions of the intestinal microbiota and the B60 group showing greater enrichment in immune-related predicted functional categories.In conclusion, BFT enhanced dietary AST utilization in L. vannamei , supporting comparable or superior culture performance at lower AST supplementation levels relative to clear-water conditions. Despite a theoretical optimum of 91.77 mg/kg AST derived from quadratic regression of WGR under BFT conditions, an 80 mg/kg supplementation level is recommended as optimal in practice when integrating growth, tissue AST deposition, coloration, immune, and economic considerations.