Ammonia tolerance by sunshine bass fry:: Implication for use of ammonium sulfate to control Prymnesium parvum

Ammonium sulfate, (NH4)(2)SO4, 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 unionized ammonia nitrogen that 4-5-d-old sunshine bass (female white bass Morone chrysops X 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)2SO(4)/L at pH 8.5 and 20degreesC-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.