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摘要
An assessment of total ammonia nitrogen (TAN) concentration was conducted for 31 ictalurid catfish ponds on six farms, in the Blackland Prairie region of Alabama (USA). Five farms that provided production data had average annual feed inputs and harvest weights of 15,579-21,739 kg ha(-1) and 8104-12,344 kg ha(-1), respectively. Concentrations of TAN were measured 26 times (weekly June through September and less frequently other months) between May 2013 and May 2014. The farm average, annual TAN concentrations were 1.05-1.78 mg L-1 at five farms and 4.17 mg L-1 at the other. Correlations were not found (P > 0.05) when pond average TAN concentration was regressed individually against feed input, weight fish harvested, and aeration rate. Nearly half of the TAN concentrations were <1 mg L-1, the majority were <5 mg L-1, but some ranged from 5 to 15 mg L-1. 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.
- 出版日期2015-2-1
