Effects of water temperature and Na+:K+ ratio on physiological and production parameters of Litopenaeus vannamei reared in low salinity water

Two experiments were conducted to examine the simultaneous effects of water temperature and Na+:K+ ratio on growth, survival, and hemolymph osmolality of Litopenaeus vannamei reared in 4‰ salinity well-water. In one study, a factorial experiment was conducted with levels of water temperature of 26 and 30 °C, and Na+:K+ ratios of 40:1, 80:1, and 120:1. Growth of shrimp was significantly higher at the Na+:K+ ratio of 40:1 than at 120:1, but not higher than at 80:1. Also, growth of shrimp was statistically greater at 30 °C than at 26 °C. Survival rate of shrimp was neither affected by Na+:K+ ratio nor by temperature. In another factorial experiment, a lower range of experimental temperatures (20 and 24 °C) and Na+:K+ ratios of 40:1 and 120:1 were tested. Both growth and survival of L. vannamei reared at the Na+:K+ ratio of 40:1 were significantly higher than at the ratio of 120:1. In turn, survival rate of shrimp, but not growth, was significantly higher at 24 °C than at 20 °C. No differences among treatments were observed for shrimp hemolymph osmolality measurements in both experiments. Results of the present study agree with previous reports of negative effects of high aqueous Na+:K+ ratio (or K+ deficient levels) on shrimp performance. At the same time, they represent the first report of a strong sensitivity of L. vannamei survival to the aqueous Na+:K+ ratio at low temperature.

► We studied effects of temperature and Na+:K+ ratio on the performance of shrimp.
► We observed negative effects of high aqueous Na+:K+ ratio on shrimp performance.
► Strong sensitivity of shrimp survival to Na+:K+ ratio occurred at low temperature.