Effects of temperature, salinity and ambient ammonia on lethal dissolved oxygen of Penaeus chinensis juveniles

Abstract 1. Lethal DO (dissolved oxygen) for Penaeus chinensis weights from 0.31 to 10.54g was 0.74 ± 0.03 mg/l in average. However, lethal time (hr) had an exponential relationship with weight. 2. Lethal DO was the highest at 35°C and the lowest at 25°C for P. chinensis juveniles exposed to 30 ppt at 15, 25 and 35°C. Lethal time (hr) was the shortest at 35°C and the longest at 25°C. 3. Lethal DO was the highest in 15 ppt and the lowest in 30 ppt among those exposed to 15, 20, 25, 30 ppt seawater at 25°C. No significant difference ( P > 0.05) of lethal time was found among four salinity levels. 4. Lethal DO increased, and lethal time decreased with increase of ambient ammonia- N in the range of 0.02 to 5.33 mg/l. Both lethal DO and lethal time of shrimps exposed to higher than 1.07 mg/l ammonia- N were significantly different ( P N ).