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.