Ammonia Tolerance by Sunshine Bass Fry: Implication for Use of Ammonium Sulfate to Control Prymnesium parvum

Ammonium sulfate, (NH4)2SO4, is recommended for controlling the toxic alga Prymnesium parvum in fish production ponds. Because the un-ionized ammonia from ammonium sulfate that kills P. parvum is also toxic to fish, we determined the maximum concentration of un-ionized ammonia nitrogen that 4–5-d-old sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) can tolerate for 48 h; this was part of a study to assess the feasibility of using ammonium sulfate in sunshine bass fingerling production ponds. We compared sunshine bass treated with six ammonium sulfate treatments— 3, 5, 8, 10, 15, and 20 mg (NH4)2SO4/L at pH 8.5 and 20°C—with untreated fish (control). Fish mortality and total ammonia nitrogen were monitored for 48 h, and un-ionized ammonia nitrogen concentrations were calculated from the total ammonia nitrogen values. Mean mortalities for all treatments were 0.0–3.3% during the first 24 h and 8.0– 37.1% after 48 h. The mean 48-h cumulative mortality was 8.0% for the control, 10.4% for ammonium sulfate concentrations of 3–15 mg/L, and 37.1% for 20 mg/L. Mean mortalities for un-ionized ammonia nitrogen concentrations of 0.0–0.25 mg/L were approximately 5–12% and were not statistically different. Mean mortality increased significantly at 0.33 mg/L of un-ionized ammonia nitrogen, resulting in 37% mortality of the fish. Because sunshine bass fry withstood un-ionized ammonia nitrogen concentrations of up to 0.25 mg/L (89% survival) and the minimum concentration of un-ionized ammonia nitrogen needed to control P. parvum is 0.17 mg/L, it appears that ammonium sulfate treatments that result in un-ionized ammonia nitrogen concentrations of 0.17 to 0.25 mg/L will control P. parvum while minimizing mortality in sunshine bass fry.