Relationship between food and growth in young crucian carps, Carassius auratus cuvieri, as determined by the nitrogen balance

Food-growth relationships in terms of the nitrogen of yearling crucian carp (Carassius auratus cuvieri) held at 20°C for 20 days and fed at various ration levels using larvae of the chironomid (Chironomus plumosus) as food, was studied.1) The efficiency of nitrogen absorption averaged 96.0%, and was independent of ration size.2) The rate of nitrogen excretion of the fed fish increased in a curvilinear manner with increases in the nitrogen absorption rate.3) The exogenous catabolic coefficient (α) : the ratio of exogenous nitrogen excretion to nitrogen absorption and net anabolic coefficient (1-α) were calculated. The net anabolic coefficients decreased exponentially with increases in the nitrogen absorption rate. Growth rate, in terms of nitrogen, was expressed by the following formula : ΔWN= AN e-a-bAN-E's where ΔWN is the nitrogen increments per gram in wet weight per unit of time, AN is the rate of nitrogen absorption, E's is a constant, and a and b are the parameters of the net anabolic coefficients.4) Gross growth efficiency, in terms of nitrogen, increased until the optimum nitrogen intake which provided the maximum efficiency was achieved, and then decreased with increases in nitrogen absorption rate. Observed values for gross growth efficiency closely approximated values predicted using the following equation : ΔWN/AN=e-a-bAN-E's/AN5) It is suggested that this equation can be applied to both low and high feeding levels but the K-line developed by Paloheimo and Dickie can only be used for higher one and is therefore likely to be of limited use in describing food-growth relationships in natural situations. Conversely, the present equation may have general applicability.