Effect of stocking density and water exchange on performance and stress tolerance to low and high salinity by Litopenaeus vannamei postlarvae reared with biofloc in intensive nursery phase

The effect of stocking density and water exchange was evaluated on growth performance of Litopenaeus vannamei postlarvae (PL), reared in a biofloc-based system at the nursery level and exposed to short-term low-high salinity stress. A bioassay was conducted with four treatments in triplicate: T₁ = 8500 postlarvae/m³ without water exchange, T₂ = 16,500 postlarvae/m³ without water exchange, T₃ = 8500 postlarvae/m³ with 50% water exchange per week, and T₄ = 16,500 postlarvae/m³ with 50% water exchange per week. At 0 (PL′22), 15 (PL′37), 30 (PL′52), and 45 (PL′67) days of culture, a group of shrimp from each treatment was exposed to acute stress by low (27 to 2‰) and high (27 to 60‰) salinity. After 45 days, the water exchange rate and water exchange rate × stocking density interaction affected shrimp survival, but shrimp growth was affected only by stocking density. The mean weight of shrimp in the treatments with the lowest stocking density was higher than that with the highest stocking density, independently from the water exchange rate. In the salinity stress tests, shrimp survival was affected by the interaction between the salinity stress tests and treatments. Generally, shrimp showed a greater tolerance when subjected to low salinity (27 to 2‰). In the culture with biofloc at the nursery level, it was confirmed that L. vannamei shrimp improve their tolerance to a sudden low salinity endpoint; a directly proportional relationship of survival with ontogenetic development in low and high salinity was determined.