High levels of total ammonia nitrogen as NH4+ are stressful and harmful to the growth of Nile tilapia juveniles - doi: 10.4025/actascibiolsci.v35i4.17291

Resumo

This study determined whether high levels of total ammonia nitrogen (TAN) as NH₄⁺ are harmful to the growth performance of Nile tilapia juveniles. Fingerlings (0.31 ± 0.04 g) were assigned to 30 polyethylene 100-L tanks in a roofed room for 12 rearing weeks. There were increasing levels of TAN by increased NH₄Cl application rates (0.0; 0.25 and 0.50 g tank^-1 week^-1) at three conditions of water pH (acidic, 6.2 ± 0.5; neutral, 7.2 ± 0.8 and alkaline, 8.8 ± 0.3). The application of HCl to acidic tanks caused 100% of TAN to be converted into NH₄⁺. The poorest growth performance results were observed for the alkaline tanks subjected to the highest application of NH₄Cl. In acidic tanks, fish survival has dropped in those tanks under the highest application rate of NH₄Cl. Tilapia growth was lower in neutral tanks when the NH₄Cl application rate increased to 0.50 g tank^-1 week^-1. It was concluded that waterborne ionized ammonia (NH₄⁺) is indirectly toxic to tilapia due to the harmful metabolites derived from it, such as nitrite and chloramines as well as due to water acidification.