Acute toxicity of ammonia on Litopenaeus vannamei Boone juveniles at different salinity levels

Litopenaeus vannamei juveniles (total length 22 +/- 2.4 mm) wen exposed to different concentrations of ammonia-N (un-ionized plus ionized ammonia as nitrogen), using the static renewal method at different salinity levels of 15 parts per thousand, 25 parts per thousand and 35 parts per thousand at pH 8.05 and 23 degreesC. The 24, 48, 72, 96 h LC50 values of ammonia-N on L. vannamei juveniles were 59.72, 40.58, 32.15, 24.34 mg l(-1) at 15 parts per thousand: 66.38, 48.83, 43.17, 35.4 mg l(-1) at 25 parts per thousand; 68.75, 53.84, 44.93, 39.54 mg l(-1) at 35 parts per thousand, respectively. The 24, 48, 72, 96 h LC50 values of NH3-N (un-ionized ammonia as nitrogen) wen 2.95, 2.00, 1.59, 1.20 mg l(-1) at 15 parts per thousand; 2.93, 2.16, 1.91, 1.57 mg l(-1) at 25 parts per thousand; 2.78, 2.18, 1.82, 1.60 mg l(-1) at 35 parts per thousand, respectively. As the salinity decreased from 35 parts per thousand to 15 parts per thousand, susceptibility of ammonia-N increased by 115%, 132%, 140% and 162% after 24, 48, 72 and 96 h exposure, respectively. The "safety level" for rearing L. vannamei juveniles was estimated to be 2.44, 3.55, 3.95 mg l(-1) for ammonia-N and 0.12, 0.16, 0.16 mg l(-1) for NH3-N in 15 parts per thousand, 25 parts per thousand and 35 parts per thousand, respectively. (C) 2001 Elsevier Science B.V. All rights reserved.