Chemical Budgets for Channel Catfish Ponds

Abstract

Budgets for water, nitrogen, phosphorus, chemical oxygen demand (organic matter), and dissolved oxygen (DO) were estimated over a growing season (March-October) for three Alabama ponds used for culture of channel catfish Ictalurus punctatus. In addition to rainfall and runoff, 190 cm of water were applied from a pipe line to offset seepage and evaporation. Production of each kilogram of live fish required 1.32 kg of feed and released to the water in metabolic wastes 51.1 g nitrogen, 7.2 g phosphorus, and 1.1 kg chemical oxygen demand (COD). Metabolic wastes resulting from production of 1 kg of fish led to the synthesis of an additional 2.59 kg of COD in photosynthesis. Thus, 1 kg of live fish resulted in 3.69 kg COD. Fish harvest accounted for only 26.8% of nitrogen, 30.1% of phosphorus, and 25.5% of organic matter (COD) applied in feed. The remainder of the nitrogen and organic matter was apparently lost from ponds for no accumulation of these substances was detected in muds. Denitrification and ammonia volatilization apparently removed large amounts of nitrogen; organic matter was consumed in respiration. Most phosphorus not harvested in fish was apparently adsorbed by muds. Seepage and overflow removed only small quantities of nitrogen, phosphorus, and organic matter. Phytoplankton photosynthesis produced large amounts of DO, but 75% of this DO was consumed by respiration of phytoplankton and other microorganisms within the water column. Total respiration within ponds exceeded DO production by photosynthesis, but diffusion usually maintained adequate DO concentrations for fish survival. However, mechanical aeration was occasionally necessary to prevent fish mortality. Received March 7, 1984 Accepted November 28, 1984