Interaction of Ionized and Un-Ionized Ammonia on Short-Term Survival and Growth of Prawn Larvae, Macrobrachium Rosenbergh

The toxicity of ammonia to Macrobrachium larvae was tested at pH 6.83, 7.60, and 8.34, and the respective 144 hr LC₅₀ values were 80, 44, and 14 mg ammonia/liter. 2. Toxicity of ammonia was not due solely to the NH₃ molecule. In solutions of different pH and equal NH³ concentrations, survival was greatly reduced as NH₄⁺ levels increased. 3. A model is proposed to explain the differential effect of ammonia as pH varies. At higher pH (8.4) toxicity results from copious diffusion of NH₃ into larvae. At lower pH (6.8) toxicity is thought to result from competitive inhibition of Na⁺ transport by NH₄⁺. 4. Retardation of growth was documented in sublethal concentrations of ammonia at 6.8 and 7.6. The average dry weight was about 26% less than that of controls (P < 0.05) after a seven day exposure. 5. Results are discussed relevant to the culture and maintenance of crustaceans, and it is concluded that ammonia will not pose a substantial threat in adequately managed systems.