Toxicity of Ammonia and Nitrite to Sunshine Bass in Selected Environments

Abstract

The effects of environmental calcium and salinity on toxicities of ammonia and nitrite for sunshine bass (female Morone chrysops × male M. saxatilis) were investigated, and the effects of pH, sodium chloride, and calcium chloride on uptake and depuration of ammonia and nitrite were characterized. The concentration of un-ionized ammonia-nitrogen (UIA-N) lethal to 50% of the fish within 96 h (96-h LC50) ranged from 0.32 to 0.60 mg/L and increased significantly with increased concentration of environmental calcium over the range tested (5–80 mg/L). The acute toxicity of UIA-N was not affected by salinity over the range tested (1–24 g/L), and the 96-h LC50 was 0.70 ± 0.04 mg UIA-N/L (mean ± SE) over all salinities tested. The rate and degree of ammonia uptake was greater at elevated environmental pH. Environmental pH did not affect the rate of depuration of ammonia. Environmental calcium did not affect nitrite toxicity, and the 96-h LC50 of nitrite-nitrogen (nitrite-N) was 12.8 ± 1.6 mg/L (mean ± SE) over all calcium concentrations tested. The 96-h LC50 of nitrite-N for fish acclimated to a salinity of 1 g/L was 35.0 ± 2.3 mg/L (mean ± SE), whereas LC50s of nitrite-N for fish acclimated to salinities of or higher than 8 g/L were greater than 100 mg/L (the highest exposure level). The addition of chloride to freshwater environments reduced the accumulation of nitrite in the plasma. Chloride was more effective in reducing the accumulation of nitrite in the plasma when added as calcium chloride rather than as sodium chloride. This study indicates that sunshine bass are relatively sensitive to both ammonia and nitrite. Tolerance to ammonia can be increased in freshwater environments by increasing calcium levels or decreasing environmental pH. Tolerance to nitrite can be increased by addition of chloride to freshwater environments or through the use of saltwater environments.