Endogenous Nitrogen Excretion and Non-fecal Energy Losses in Carp and Rainbow Trout

Abstract

This series of studies on nutritional energetics in carp and rainbow trout aims to provide basic data necessary for standardization of feed quality evaluation for fish in captivity. At the outset, endogenous nitrogen excretion (ENE) through the gills and in the urine was determined by feeding a non-protein diet which is essential for calculation of metabolizable energy. The amounts of ENE in carp of 21-289 g were 5.6-9.3 mg/lOOg body weight/day and decreased with increase of fish body weight and with decrease of water temperature. The rates of ENE were 10.0-15.7mg/100g BW/day for carp weighing below 20g. The ENE rates in rainbow trout were proportional to water temperature, ranging from 6.6 mg at 14°C to 12.4 mg at 21°C (9.0 mg on average). Secondly, to determine non-fecal energy losses carp or rainbow trout weighing more than 100 g were fed four kinds of experimental diets. There were no marked differences in the non-fecal losses among the fish fed the same diet once or three times daily at almost the same feeding levels. The proportion of energy lost through non-fecal wastes seems to be not so influenced by temperature. © 1995, The Japanese Society of Fisheries Science. All rights reserved.