LETHAL EFFECTS OF AMMONIA ON PENAEUS-CHINENSIS OSBECK JUVENILES AT DIFFERENT SALINITY LEVELS

Penaeus chinensis Osbeck juveniles (3.61 +/- 0.23 cm) were exposed to different concentrations of ammonia, using the static renewal method, in different salinity levels at pH 8.12 and 25-degrees-C. The 24, 48, 96 and 120-h LC50 value of ammonia-N (un-ionized plus ionized ammonia as nitrogen) on P. chinensis juveniles was 66.73, 53.94, 42.44 and 39.87 mg.l-1 at 30 parts per thousand; 52.20, 42.65, 38.87 and 37.83 mg.l-1 at 20 parts per thousand; and 44.02, 34.77, 28.18 and 24.34 mg.l-1 at 10 parts per thousand. The 24, 48, 96 and 120-h LC50 value of NH3'-N (un-ionized ammonia as nitrogen) was 3.88, 3.13, 2.47 and 2.32 mg.l-1 at 30 parts per thousand; 3.31, 2.70, 2.46 and 2.40 mg.l-1 at 20 parts per thousand; and 3.03, 2.39, 1.94 and 1.68 mg.l-1 at 10 parts per thousand, respectively. As the salinity decreased from 30 to 10 parts per thousand, susceptibility increased 154% for ammonia-N and 130% for NH3-N. The "threshold" was found at 144 h, and the "incipient LC50" for P. chinensis juveniles was 38.12, 36.01 and 22.77 mg.l-1 for ammonia-N (2.21, 2.28 and 1.57 mg.l-1 for NH3-N). The "safety level" for rearing P. chinensis juveniles was estimated to be 3.81, 3.60 and 2.23 mg.l-1 for ammonia-N (0.22, 0.22 and 0.16 mg.l-1 for NH3-N) in 30, 20 and 10 parts per thousand, respectively.