ACUTE TOXICITY OF AMMONIA TO VARIOUS LIFE STAGES OF THE SAO-PAULO SHRIMP, PENAEUS-PAULENSIS PEREZ-FARFANTE, 1967

Each life stage of the Sao Paulo shrimp, Penaeus paulensis, was exposed to ammonia in a series of acute toxicity tests, by the semistatic method, at 25 degrees C and salinity at 28 ppt. A pronounced sensitivity was observed in the egg stage, In this phase, 0.30 mg/l NH3-N caused death of 50% of the embryos. The 24-h LC(50) values for nauplii, zoeae, myses and postlarvae were, respectively, 102.30, 22.93, 74.87 and 24. 19 mg/l total ammonia-N (4.25, 1.79, 2.91 and 1.40 mg/l NH3-N). The 96-h LC(50) values for zoeae, myses and postlarvae were 9.39, 21.98, 5.49 mg/l total ammonia-N (0.73, 0.85 and 0.32 mg/l NH3-N). The LC(50) Of ammonia for juveniles (5.45 +/- 0.4 g mean live-weight) and for adults (31.43 +/- 1.3 g mean live-weight) were also measured. The 24-h LC(50) values for juveniles and adults were, respectively, 51.87 and 61.63 mg/l total ammonia-N (1.47 and 1.59 mg/l NH3-N) and the 96-h LC(50) values were 38.72 and 42.49 mg/l total ammonia-N (1.10 and 1.06 mg/l NH3-N). An analysis of variance showed that there was no direct relationship between shrimp development and its tolerance to ammonia (P > 0.05) and that eggs, zoeae and postlarvae are very sensitive to ammonia:. The ''safe level'' for rearing P. paulensis was estimated to be 0.03 mg/l NH3-N. In general, P. paulensis is less resistant to ammonia than other species of shrimp.