Acute and chronic effects of ammonia in the South African abalone, Haliotis midae Linnaeus (Mollusca)
Ammonia is the major end-product of protein catabolism in abalone, and is excreted into the surrounding water. Build-up of ammonia in abalone aquaculture systems can reach high toxic levels and impact negatively on farming operations. Ammonia levels therefore have to be regulated. Accurate estimates of toxic un-ionized ammonia (FAN) from the total ammonia nitrogen (TAN) measured by photometer test kits is crucial as inaccuracies could result in major losses of abalone on the farms. The accuracy and applicability of two frequently used photometer test kits (the Nesslers method and the Palintest method) were compared. The calculated TAN concentrations were regressed against the prepared standard ammonia concentrations in seawater for both methods. The predicted slope (β = 1) if the methods were 100% accurate was compared to observed slopes using the Nesslers (β=0.8327) and Palintest (β = 0.7507) methods. Both these test kits underestimated the TAN concentrations, but the Nesslers method was more accurate. Nitrites and nitrates are toxic to abalone at much larger concentrations than ammonia and exist at low concentrations in natural systems, therefore the sensitivity of their tests was not as important. Nitrites and nitrates were monitored using the Ferrous sulphate method and the Cadmium reduction method, respectively.
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