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 degrees 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 degrees C than at 26 degrees 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 degrees 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 degrees C than at 20 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.