Impact of low-protein diets with varied lipid levels on growth, metabolism of Penaeus vannamei, and carbon and nitrogen cycling in biofloc systems

Abstract

Biofloc technology (BFT) enhances shrimp farming sustainability by improving water quality and reducing external feed inputs. While protein and lipid requirements for Penaeus vannamei in BFT systems are lower than in traditional systems, the optimal lipid level under low-protein diets remains unclear. This study examined the effect of low-protein diets with varying lipid levels on the growth, metabolism, and nutrient cycling of P. vannamei in biofloc systems. Five diets with fixed 29 % protein and lipid levels ranging from 5 % to 13 % were tested, with the control diet containing 35 % protein and 8.6 % lipid. Results showed that lipid levels did not significantly affect biofloc composition, but shrimp growth was optimized at 10.04 %–10.14 % lipid. Higher lipid levels boosted lipase and CAT activity, while amylase, trypsin and SOD activities remained unchanged. Higher lipid levels (11 %–13 %) improved nitrogen retention and utilization. Microbial analysis indicated Leucothrix mucor played a role in nitrogen assimilation, with increased expression of genes related to the DNRA pathway in 9 % lipid group. Although carbon budgeting was unaffected by lipid levels, carbon loss remained high among all groups, potentially due to incomplete utilization of glycolysis and acetate metabolism or shrimp molting. This study highlights the potential for optimizing nutrient strategies in BFT systems to improve feed efficiency and support sustainable shrimp farming.