ABSTRACT
Ammonia is the principle nitrogenous by-product of fish metabolism and is of importance in fish culture because it is toxic to fish in its un-ionized form. The origin of metabolic ammonia is the deamination of amino acids utilized as energy. A metabolic nitrogen budget allows for the estimation of the contribution of dietary protein to the accumulation of ammonia in water. For every 100 g of protein fed, approximately 40 g will be assimilated as fish flesh. If 20 g are undigested and 5 g are uneaten, 35 g will be metabolized as energy (Lovell 1989). Protein is approximately 16% nitrogen. Thus, fish consumption of 100 g of dietary protein will result in 35 g × 16%, or 5.6 g of ammonia being excreted. The ammonia production rate may be expressed as A = 56 P https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315194813/e90b7e7a-d3c7-4b6f-a2cd-a17db44dff19/content/math1_9_1.jpg"/> where A = the ammonia production rate in g total ammonia nitrogen (TAN) per kg of food and P = the decimal fraction of protein in the diet. For example, feeding a 45% protein diet would result in the production of 25.2 g of ammonia nitrogen per kg of food fed. In this book, unless stated otherwise, concentrations of all nitrogenous species are expressed as mg/L of nitrogen, which is consistent with most of the literature.
