An assessment of total ammonia nitrogen concentration in Alabama (USA) ictalurid catfish ponds and the possible risk of ammonia toxicity

Analysis of the literature on ammonia toxicity to channel catfish suggested that the no-observed-effect level (NOEL) is around 1.0 mg L− 1 NH3-N in ponds with pH of 7.5 and above where NH3-N concentration fluctuates greatly because of daily change in temperature and especially pH. Based on the daily pH fluctuation of 7.5 to 9.5 observed in ponds, and typical monthly average water temperatures, the NOEL for NH3-N was often exceeded. At pH 8.5-8.9, depending upon the month, up to 14.5% of ponds exceeded the NOEL for NH3-N. The NOEL was exceeded by up to 31.5% of pond at pH ≥ 9.0. The findings reveal that TAN concentrations in Alabama ponds often are at chronically toxic levels for ictalurid catfish. There is usually no practical emergency treatment for reducing NH3-N (or TAN) concentration in ponds exceeding the NOEL. Thus, good management practices for avoiding excessively high TAN concentrations in ponds - efficient feed management, adequate aeration to promote nitrification, and treatments for maintaining buffering capacity in pond water should be applied.