TOXICITIES OF AMMONIA AND NITRITE TO PENAEUS-MONODON ADOLESCENTS

Penaeus monodon adolescents (91.0±8.0 mm) were exposed to various concentrations of ammonia (NH3+NH4+) and nitrite in 20 ppt seawater at a pH of 7.57 and a water temperature of 24.5°C using the static renewal method. The LC50 values of ammonia-N (un-ionized plus ionized ammonia as nitrogen), NH3-N (un-ionized ammonia-N) and nitrite-N decreased with longer exposures. The 24-, 48-, 96- and 144-h LC50 values were 97.9, 88.0, 53.4 and 42.6 mg/l of ammonia-N (1.76, 1.59, 0.96 and 0.77 mg/l of NH3-N), respectively. The 24-, 48-, 96-, 144-, 192- and 240-h LC50 values of nitrite-N were 218, 193, 171, 140, 128 and 106 mg/l nitrite-N, respectively. The "thresholds" of ammonia and nitrite toxicity were found at 144 and 240 h, respectively, on a toxicity curve approaching an asymptote. Based on the incipient LC50 value and an application factor of 0.1, safe values for rearing adolescent P. monodon (20 ppt, 7.57 pH, 24.5°C) were calculated to be 4.26 mg/l ammonia-N, 0.08 mg/l NH3-N and 10.60 mg/l nitrite-N. © 1990.