High levels of total ammonia nitrogen as NH 4 + are stressful and harmful to the growth of Nile tilapia juveniles - doi: 10.4025/actascibiolsci.v35i4.17291

Abstract

This study determined whether high levels of total ammonia nitrogen (TAN) as NH 4 + are harmful to the growth performance of Nile tilapia juveniles. Fingerlings (0.31+or-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 NH 4 Cl application rates (0.0; 0.25 and 0.50 g tank -1 week -1) at three conditions of water pH (acidic, 6.2+or-0.5; neutral, 7.2+or-0.8 and alkaline, 8.8+or-0.3). The application of HCl to acidic tanks caused 100% of TAN to be converted into NH 4 +. The poorest growth performance results were observed for the alkaline tanks subjected to the highest application of NH 4 Cl. In acidic tanks, fish survival has dropped in those tanks under the highest application rate of NH 4 Cl. Tilapia growth was lower in neutral tanks when the NH 4 Cl application rate increased to 0.50 g tank -1 week -1. It was concluded that waterborne ionized ammonia (NH 4 +) 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.