Effects of different concentrations of sodium humate on the growth, enzyme activity and water microflora of Pacific white shrimp ( <i>Litopenaeus vannamei</i> ) based on the zero-water exchange model

In the present study, the effect of sodium humate on growth performance, enzyme activity, and water column microflora of Litopenaeus vannamei was investigated using a zero-water exchange culture model. Different concentrations of sodium humate were added to the culture water during the 54-day experimental period. The results showed that the growth indexes such as shrimp specific growth rate and survival rate were significantly better in the 3 mg/L addition group (sodium humate) than in the control group (p&lt;0.05); and the 12 mg/L addition group had the most significant effect in reducing the levels of ammonia nitrogen and nitrite nitrogen in the water column (p&lt;0.05). In terms of enzyme activities, lipase, trypsin, superoxide dismutase, and lysozyme activities were the highest in the 9 mg/L addition group (p&lt;0.05), while catalase and phenol oxidase activities were the greatest in the 6 mg/L and 12 mg/L addition groups (p&lt;0.05). Microbiological analyses showed that the control group had the least heterotrophic bacteria, but Vibrio counts were significantly higher than those of the additive group (p&lt;0.05). The bacterial diversity was higher in the additive group than in the control group (p&lt;0.05) and had different dominant flora at the genus level. The experimental results show that sodium humate can improve the water quality and substrate environment, enhance the antioxidant capacity of shrimp, and promote their growth and survival. It can effectively reduce the concentration of ammonia nitrogen and nitrite nitrogen in the water body, inhibit the growth of Vibrio , and optimize the diversity and structure of the water body microecology. In conclusion, the addition of sodium humate to shrimp aquaculture water can significantly enhance the growth performance of shrimp, improve the microecology of the water body, and provide a theoretical basis and practical guidance for eco-friendly shrimp aquaculture.