Nitrogen Budget in the Carp Rearing Tank

Abstract

Nitrogen in the feed ingested by fish is balanced quantitatively by growth in body nitrogen, excreted nitrogen and nitrogen in egested faeces. Judging from growth efficiency of fish, a large proportion of the ingested nitrogen is removed to the rearing water in various forms of nitrogen as metabolic waste and egested faeces. It may be considered, therefore, that abundant nitrogen as food has a harmful influence upon the aquatic environment in the rearing tank.
This paper describes the nitrogen flow in the tank from the viewpoint of the nitrogen budget. Every item in the budget was estimated independently and measured as directly as possible.
The nitrogen load as feed into the tank is 0.282 g-N/l during 44 days of the rearing period. This nitrogen load converts to 0.123 g-N/l or 43.6% of DON, 0.028 g-N/l or 9.9% of PON, 0.027 g-N/l or 9.6% of DIN, 0.097 g-N/l or 34.4% of growth and 0.007 g-N/l or 2.5% of other. Total organic nitrogen concentration (DON+PON) increases at the rate of about 50% of the nitrogen load.