Fish Production, Water Quality, and the Importance of Nitrification as an Ammonia Removal Process in Intensively Aerated Hybrid Catfish Ponds

Authors: Ott, Brian; TORRANS, E - Retired ARS Employee; TUCKER, CRAIG - Retired ARS Employee

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2024
Publication Date: 12/3/2024
Citation: Ott, B.D., Torrans, E.L., Tucker, C.S. 2024. Fish Production, Water Quality, and the Importance of Nitrification as an Ammonia Removal Process in Intensively Aerated Hybrid Catfish Ponds. Journal of the World Aquaculture Society. 55(6)e13094. https://doi.org/10.1111/jwas.13094.
DOI: https://doi.org/10.1111/jwas.13094

Interpretive Summary: Ammonia can limit production of catfish at high stocking densities and even become lethal under certain circumstances. Most ammonia is taken up by phytoplankton, but once maximum biomass of the phytoplankton population is reached, ammonia can begin to accumulate to possibly toxic levels. Scientists at the USDA-ARS Warmwater Aquaculture Research Unit conducted this study to determine what the limits of catfish production are in small, intensively aerated earthen ponds and if ammonia accumulation would impair fish production. Stocking density did not impact survival, but decreased average fish harvest weight and increased FCR. Once the maximum population of phytoplankton was reached, excess ammonia was oxidized by bacteria into nitrite and ultimately nitrate. These results demonstrate that production potential of catfish ponds is likely much higher than previously thought and that multiple mechanisms can eliminate ammonia from the system.

Technical Abstract: This study evaluated interactions among fish stocking densities, feeding rates, fish production, and water quality in intensively aerated ictalurid catfish ponds over a wide range of production intensities. Emphasis was given to concentrations of combined inorganic nitrogen species to elucidate factors affecting ammonia concentrations over a range of nitrogen loading rates. Six 0.1-ha earthen ponds with 45 kW/ha of aeration capacity were stocked with hybrid catfish (Ictalurus punctatus ['] x I. furcatus [']) at rates ranging from 15,000 to 90,000 fish ha-1 in 15,000 fish ha-1 increments to analyze the effect of nitrogen loading on ammonia accumulation and fish production. Daily minimum dissolved oxygen concentrations were maintained above 3.0 mg O2 L-1 to prevent dissolved oxygen concentrations from decreasing fish appetite. Stocking density did not impact survival but decreased average fish weight and increased food conversion ratio (FCR). Gross production increased with stocking density and ranged from 7,249 to 35,674 kg/ha. Average total (TAN) and un-ionized ammonia (NH3) were not different among stocking densities despite greater nitrogen inputs in ponds with higher feeding rates. Nitrite (NO2-) and nitrate (NO3-) concentrations were significantly higher in ponds with higher stocking densities, suggesting that nitrification rates increased with nitrogen loading. Phytoplankton assimilation of ammonia is the primary ammonia removal process in traditional catfish ponds with modest fish densities and feeding rates. However, in intensively aerated ponds with high feeding rates, nitrification can become an important process for ammonia removal. These data indicate that small earthen hybrid catfish ponds with high aeration capacities can increase catfish production without ammonia accumulating.