Determination of Total Ammonia Nitrogen and Chemical Oxygen Demand in Fish Culture Systems

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Abstract
Total ammonia nitrogen (TAN) was measured by the phenate method on filtered and distilled portions of samples from waters used for intensive fish culture. There was a high correlation (r = 0.987; P < 0.01) between TAN values for filtered and distilled portions of samples. The slope and the y‐intercept of the regression line did not differ from 1.0 and 0.0, respectively, indicating close agreement between magnitudes of TAN values for filtered and distilled samples. The average percentage recovery of 0.30‐mg/liter additions of total ammonia nitrogen to samples was 96.4% for distilled portions and 96.7% for filtered portions. Precision of the two versions of the phenate method did not differ. A simple heat‐of‐dilution chemical oxygen demand (COD) technique was developed which yielded values highly correlated with standard COD values (r = 0.970; P < 0.01). The heat‐of‐dilution technique was as precise as the standard COD method, but did not oxidize organic matter as completely. COD values by the heat‐of‐dilution method averaged 60.2 % of standard COD values. Nevertheless, there was a high correlation (r = 0.86; P < 0.01) between heat‐of‐dilution COD concentrations and consumption of oxygen by organisms in water samples. The heat‐of‐dilution COD technique appears highly applicable in fish culture.

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