Feed the Future Innovation Lab for Collaborative Research on Aquaculture & Fisheries

Two experiments were conducted to better understand the role of urea in pond fertilization. In Experiment 1, urea dissolved in pond water and incubated in aquaria at approximately 30°C disappeared at a rate of 303 μg urea-N l⁻¹ day⁻¹ under natural sunlight conditions, and 102 μg urea-N l⁻¹ day⁻¹ under dark conditions. Total alkalinity decreased in dark aquaria and increased in sun-exposed aquaria, consistent with stoichiometric expectations. Urea hydrolysis was negligible in distilled water exposed to light. Experiment 2 was a toxicity test. Median lethal concentrations (LC50'S) of urea at 24 and 96 h exposure were 19,700 mg l⁻¹ and 16,800 mg l⁻¹ for sex-reversed male Nile tilapia (Oreochromis niloticus) fingerlings, and 17,000 mg l⁻¹ and 16,000 mg l⁻¹ for silver barb (Puntius gonionotus) fingerlings, respectively. All test fish survived 96-h exposure to 14,000 mg urea l⁻¹, whereas no fish survived 48-h exposure to 22,000 mg urea l⁻¹.

NOP 93-59 (English) (French) (Spanish)