Ammonia Production Rates of Three Commonly Cultured Fish Species in Aquaponics Systems

Aquaponics is the combination of soilless plant culture, or hydroponics, with recirculating aquaculture systems (RAS). The most prolific waste product generated in RAS is typically ammonia, which is ultimately converted via the nitrification cycle into nitrate, the preferred form of nitrogen for most plants. Since the amount of available nitrate in an aquaponic system is a direct result of ammonia production, a method for accurately manipulating ammonia levels is of utmost importance. An experiment was conducted to determine the daily amount of ammonia excreted per gram of each fish species using several feeds with differing protein concentrations. Trials were run using hybrid striped bass, koi, and tilapia. The experiment consisted of 6 feed diets and 3 replications. The feed diets used were 28, 32, 35, 40, and 44% protein, plus a control group that received no feed. The pH and ammonia levels of each tank were recorded daily using a pH meter and ammonia spectrophotometer, respectively. These trials demonstrated an increase in ammonia production that paralleled the increase in protein content of feed. Although there were differences in amounts produced between fish species, all species experienced a similar trend of increased ammonia production correlated with an increase in dietary protein intake. These findings are important as they can help producers manipulate the diet of their fish stock to produce a level of nitrogen that is neither deficient nor excessive for their selected vegetable crops. This ensures that vegetable crops maintain adequate growth rates, and that excessive feeding does not occur to minimize overall expenses.