Growth, body composition, respiration and ambient ammonia nitrogen tolerance of the juvenile white shrimp, Litopenaeus vannamei, at different salinities

Trials were conducted in laboratory to investigate the growth performance, body composition, respiration and ammonia-N tolerance of the white shrimp, Litopenaeus vannamei, at 3.0, 17.0 and 32.0‰, respectively. In the growth trial, 40 juvenile shrimps were stocked into each tank with four replicates at each salinity, and were fed with a commercial diet for 50 d. Shrimp weight gain at 17.0‰ was the highest, and significantly higher than that of shrimps at 3.0‰. Shrimp survival rate at 3.0‰ was significantly lower than that of other two groups. However, hepatosomatic index and condition factor were not significantly affected by the ambient salinity. Shrimp body protein and ash content were not affected significantly by salinity, while body moisture increased at high salinity, and crude lipid in shrimps was lowest at 32.0‰. After being exposed to the above three salinities for 30 d prior to the test, shrimp oxygen consumption and respiratory quotient of the shrimps at 3.0‰ were significantly higher than those of shrimps at medium and high salinities, while salinity did not significantly affect CO₂ production. When juvenile L. vannamei were exposed to seven ammonia-N concentrations (0, 4.00, 6.67, 9.33, 12.00, 14.67, and 17.33 mg l^{- 1}) at the three above salinities to which shrimps had been separately acclimated for 10 d at pH 8.30 and 29 ± 0.5 °C, shrimps at 3‰ were the most susceptible to ambient ammonia-N, and the 96 h LC50 with 95% confidence limit to ambient ammonia-N was 9.33 (8.39-10.37) mg l^{- 1}. This study suggests that L. vannamei could adapt to a wide range of salinity, but the animals would be more susceptible to ammonia toxicity and spend more energy to compensate the cost for osmoregulation at low salinity.