Water quality in an existing 0.65 ha watershed pond with a maximum depth of 4.6 m was monitored before and after installation of floating raceways. Grass and koi carp were stocked in 2016 to control rooted aquatic vegetation. Large catfish and paddlefish were stocked on top of largemouth bass and bluegill populations. Vertical circulation to destratify water began in 2018 and horizontal circulation began when floating raceways were installed in 2019. Intensive feeding of channel catfish occurred in 2021 with maximum daily feed input of 102 kg/day. Largemouth bass production in 2022 resulted in much lower feed input.
Sampling of water quality began in 2017 and continued throughout the project. Dissolved oxygen concentration (DO) and temperature were measured at 30 cm intervals to generate a profile over a depth of 3 m. Weekly grab samples taken at the water surface was analyzed for total ammonia nitrogen (TAN), nitrite, nitrate, alkalinity and pH.
Without circulation, the pond stratification was evident during summer months when dissolved oxygen concentration and water temperature decreased with increasing water depth. As expected, circulation eliminated stratification and created relatively uniform DO throughout the water column. The first year of full production occurred in 2021 when each of three raceways were stocked with 4,400 stocker catfish (158 g/fish). During the year approximately 10,400 kg feed pellets were fed to fish in the raceways and pond. TAN rose to a mean of 1.28 in June and sustained or rose above this level through October. Nitrite rose to 0.186 mg/L in July and did not fall below this level until November. Increased nutrient input significantly impacted water quality, disease pressure, and feeding opportunity. Our protocol has changed to limit the amount of feed applied to 9000 kg/ha annually if there is no removal of solid waste.