TOXICITY OF AMMONIA, NITRITE, AND NITRATE TO JUVENILE AUSTRALIAN CRAYFISH, CHERAX-QUADRICARINATUS

Survival rates and metabolic (oxygen consumption) rates were examined in juvenile Australian crayfish, Cherax quadricarinatus, exposed to di fferent concentrations of ammonia, nitrite, or nitrate. The relative t olerances of these crayfish to ammonia, nitrite, and nitrate are simil ar to those reported for other fish and crustacean species. No mortali ties were observed in crayfish exposed to concentrations up to 25 mg/L total NH3-N (0.54 mg/L un-ionized NH3-N). Crayfish exposed to 50, 100 , and 200 mg/L total NH3-N (1.07, 2.14, and 4.28 mg/L un-ionized NH3-N ) survived an average of 40, 36, and 14 hr, respectively. Calculated L C(50) values for 24, 48, and 96 hr were 94.3 +/- 0.24, 76.3 +/- 0.13, and 45.9 +/- 0.25 mg/L total NH3-N, respectively (2.02, 1.63, and 0.98 mg/L un-ionized NH3-N). No mortalities were observed in crayfish expo sed to concentrations up to 10 mg/L NO2-N. Crayfish exposed to 25, 50, and 100 mg/L NO2-N survived an average of 96, 22, and 5 hr, respectiv ely. Calculated LC(50) values for 24, 48, and 96 hr were 42.9 +/- 0.22 , 37.1 +/- 0.16, and 25.9 +/- 0.35 mg/L NO2-N, respectively. No mortal ities were observed in crayfish exposed to nitrate concentrations up t o 1000 mg/L. Oxygen consumption rates of crayfish exposed to fresh wat er (controls) were regulated over the PO2 range of 20 to 5 kPa. Oxygen consumption rates of crayfish exposed to ammonia or nitrate did not d iffer significantly from those of control crayfish over the same range of environmental PO2. Oxygen consumption rates of crayfish decreased immediately upon exposure to nitrate and were never recovered. At 10 k Pa PO2, oxygen consumption rates of crayfish exposed to nitrite were a pproximately 50% of controls. In conditions of low environmental PO2, nitrite could substantially affect the survival of individuals.