OBSERVATIONS OF AN INVERSE AMMONIA TOXICITY RELATIONSHIP IN THE BRINE SHRIMP Artemia

Brine shrimp are known to be capable of survival, growth, and reproduction in extreme environments of salinity, pH and total ammonia nitrogen concentration. Reported free ammonia LC₅₀ values for brine shrimp have been observed to be in excess of 100 mg/l compared to less than 1 mg/l for most other aquatic animals.  However catastrophic toxicity in brine shrimp culture has been reported at low levels of free ammonia in low pH waters.  

Laboratory experiments were conducted to shed light on the relationship between ammonia toxicity and pH in adult Artemia.  A matrix of acute ammonia exposures of brine shrimp to free ammonia ranging from 0.001 to 200 mg/l at pH values of 7.0, 7.5, 8.0, 8.5, 9.0 and 9.5 was designed and conducted. Ten adult brine shrimp were placed in 250 ml Erlenmeyer flakes and exposed for 24 hrs.  Solution pH was adjusted and maintained with additions of either CO₂ or Na₂CO₃. At the end of 24 hrs the results were used to establish 24 hr LC₅₀ values of free ammonia and total ammonia nitrogen (TAN) at varying pH levels. The results suggest that in spite of exponentially increasing free ammonia at elevated pH, brine shrimp mortality at pH 7.0 was radically more severe as opposed to pH 9.5. The observed LC₅₀ for free ammonia at pH 7.0 was only 0.016 mg/l compared to LC₅₀ value of 155 mg/l at pH 9.5.

Apparently, brine shrimp are capable of employing some form of protective mechanism allowing them to resist free ammonia toxicity at high solution pH. This observation has important consequences in understanding how brine shrimp are capable of growth in heavy algal bloom conditions where culture pH is often elevated. Furthermore, this characteristic has important implications in management of high density brine shrimp culture for use in harvesting and converting algal or bacterial cultures into brine shrimp biomass