Acute Toxicity of Ammonia and Nitrite to Spotted Seatrout

Abstract Median lethal concentrations (LC50) of ammonia and nitrite were determined for spotted seatrout (Cynoscion nebulosus) in static tests. Ammonia toxicity tests were conducted with eggs, larvae hatched from eggs previously exposed to ammonia (ammonia-exposed eggs), larvae hatched from eggs not previously exposed to ammonia (unexposed eggs), 1-month-old juveniles, and 4-month-old juveniles. Nitrite toxicity tests were conducted with eggs and larvae. Spotted seatrout eggs were the life history stage most tolerant of un-ionized ammonia; 91.6% hatch occurred at 6.0 mg NH3-N/L. The 24-h LC50 for larvae hatched from both ammonia-exposed and unexposed eggs was 0.28 mg NH3-N/L. The 24-h LC50 of nitrite for larvae was 980 mg NO2-N/L; 92% hatch occurred at 1,200 mg NO2-N/L. Tolerance of un-ionized ammonia increased with age through the 4-month juvenile stage; the respective 24-h NH3-N LC50s for 1 - and 4-month-old juveniles were 1.38 and 1.98 mg/L, and the respective 96-h LC50s were 0.98 and 1.72 mg/L.