Investigations of Ammonia Nitrogen in Aquaculture：the Methodology, Concentrations, Removal, and Pond Fertilization

Abstract

Four investigations were performed related to ammonia nitrogen in aquaculture. The first investigation compared the precision and accuracy of (1) Nessler, (2) phenate, (3) salicylate, and (4) ammonia electrode procedures for total ammonia nitrogen (TAN) concentration determination in waters of aquaculture. Salicylate method was selected as a standard method for its high precision and accuracy. Addition of Rochelle salt increased the precision and accuracy for TAN analyses by the Nessler method. TAN analyses by the phenate I and the salicylate methods were not different in freshwater. The salicylate kit method is a suitable alternative to the standard salicylate method, while the Nessler kit is not. Electrodes for sensing NH3 and NH4+ were less precise or accurate in most cases. The second investigation assessed TAN concentration in 31 ictalurid catfish ponds on six farms, in the Blackland Prairie region of Alabama (USA). 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. Nearly half of the TAN concentrations was < 1 mg L-1, the majority was < 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. The findings reveal that TAN concentrations often are at chronically toxic levels for ictalurid catfish in Alabama ponds. There usually is no practical emergency treatment for reducing NH3-N (or TAN) concentration in ponds exceeding the NOEL. Use of good management practices is recommended to avoid excessively high TAN concentrations. The third investigation studied the effectiveness of two processed samples of New Zealand mordenite for possible use in removing total ammonia nitrogen (TAN) in aquaculture application. The percentage reduction in TAN concentration in 100-mL solutions held on a rotating shaker increased linearly with greater mordenite application rate, while the amount of TAN removed per gram of mordenite (adsorptive efficiency) declined. Ammonia removal and adsorptive efficiency decreased with increasing salinity up to 30 g L-1. Although mordenite is capable of reducing TAN concentration in water of laboratory tests, it probably is not highly effective for this purpose in aquaculture ponds. The fourth investigation studied the bluegill yield in response to nitrogen and phosphorus versus phosphorus-only fertilization in ponds at different times since sediment removal. The experiment was conducted in 40-yr-old research ponds at the Auburn University E. W. Shell Fisheries Center from which sediment had been removed 2 to 9 yr earlier to restore bottoms nearly to their original soil composition. Bluegill production was uncorrelated with time since sediment removal in ponds treated only with phosphate fertilizer. Soluble reactive phosphorus and total ammonia concentration were correlated with time since sediment removal (R2 = 0.312 and R2 = 0.514, respectively, P < 0.05). Results suggest pond managers might omit nitrogen fertilizer if phytoplankton blooms do not wane after only 2 yr of fertilization with nitrogen and phosphorus.