Key water environmental factors regulating growth of Litopenaeus vannamei in small-shed pond culture: effects driven by organic matter accumulation and redox process

To identify the key water environmental factors governing the growth of Litopenaeus vannamei in small-shed pond culture systems, and to elucidate the relationship between differences in nitrite ( ${\mathrm{N}\mathrm{O}}_2^{-}\text{-}\mathrm{N}$) concentration and variations in microbial community composition within these systems, we continuously monitored shrimp growth and the dynamic changes in physicochemical parameters of aquaculture water over a 90-day culture cycle in a small-shed pond aquaculture system in Taishan, Guangdong Province. In addition, we analyzed the microbial community composition and predicted functions at different nitrite concentration levels. Spearman correlation analysis revealed that, the water physicochemical parameters such as ammonia nitrogen ( ${\mathrm{N}\mathrm{H}}_4^{+}\text{-}\mathrm{N}$), ${\mathrm{N}\mathrm{O}}_2^{-}\text{-}\mathrm{N}$, chemical oxygen demand (COD), oxidation-reduction potential (ORP), and total alkalinity (T-Alk) were all significantly correlated with the absolute body-mass growth rate of L. vannamei (p<0.05). Multiple regression analysis further revealed that COD and ORP were the dominant negative and positive factors affecting the absolute growth rate of body mass, with contribution rates of 40.9% and 36.7%, respectively. Microbial community analysis of water, sediment, and shrimp gill on Day 56 showed that the relative abundances of Proteobacteria and Vibrio in the sediment of ponds with high nitrite concentrations were significantly higher than those in the medium- and low-concentration groups (p<0.05). PICRUSt2-based functional prediction further indicated that high-nitrite conditions promoted a functional shift of microbial communities in sediment, water, and shrimp gill toward opportunistic pathogen colonization, stress adaptation, and competitive restructuring, while weakening system self-purification capacity and gill homeostasis. In conclusion, this study reveals the associative effects and potential risks of ''organic matter accumulation-redox imbalance-microbial functional shift'' in small-shed pond culture systems, providing a reference for optimizing water quality management strategies in such systems.