Effects of Chronic Ammonia Exposure on Growth of Genetically Improved Farmed Tilapia (GIFT) Cultured Under Different Densities

Abstract

AbstractTilapia are among the most widely cultivated fish species in the world, with a high level of importance for freshwater fish production. An important tilapia variety for the international market is genetically improved farmed tilapia (GIFT; Nile Tilapia Oreochromis niloticus). Multiple studies have been developed to determine the maximum concentrations of ammonia (NH3) recommended for the cultivation of various varieties of tilapia; however, there are no specific data for the cultivation of GIFT. Growth results for GIFT fry exposed to NH3 at 0.50, 0.89, and 1.58 mg/L in 69‐d chronic toxicity tests were evaluated. The experiments were conducted in three recirculation aquaculture systems, one for each concentration of NH3. Stocking densities were 33, 66, and 132 fish/m3. Fish were fed ad libitum three times per day. The only mortalities recorded were for treatments with the highest NH3 concentration (1.58 mg/L), which had a cumulative mortality of 89.5%. There were no significant differences in weight gain for the three stocking densities assessed at an NH3 concentration of 0.50 mg/L. Results indicated that GIFT juveniles can be cultured with stocking densities of up to 132 fish/m3 in environments with ammonia concentrations of up to 0.89 mg/L without compromising fish survival, although the daily weight gain was between 30% and 41% lower than the values reported for optimal culture conditions.