Your article perpetuates a common error regarding pond aquaculture when it states, “These systems all rely on large volumes of clean water flowing to the fish and carrying waste away.” In the catfish industry (the largest pond-culture venture in the United States), ponds are only emptied for renovation once every 10 to 20 years, and fresh water is added only to make up evaporation losses. Waste is degraded in the pond by the same bacteria that inhabit biofilters in recycling systems. Conversely, the recirculating systems described in the article commonly rely on partial daily water changes, and the water discharged carries a concentrated load of nutrients.

Andy Goodwin
University of Arkansas
Pine Bluff, Ark.