Effect of Feeding on Nitrogen Excretion of Japanese Flounder Paralichthys olivaceus.

Abstract

Measurements of the rate of nitrogen excretion were carried out with fed and starved Japanese flounder of 163 to 575g in body weight at 20°C. Ammonia-N and urea-N excretion of the starved fish were 0.20±0.05mg-N/100g/h and 0.04±0.02mg-N/100g/h, respectively. Immediately after feeding, the rate of ammonia-N excretion per hour of the flounder became 3 to 4 times that of the starved fish. These elevated rates continued for 12, 30 and more than 36h, at 0.5, 1.0 and 1.5% rations, respectively. In contrast to ammonia-N excretion, the rate of urea-N excretion per hour of the fed fish showed a major peak during the period of 6-12 or 12-24h after feeding. In Japanese flounder fed on the pelleted diet containing 7.5% of nitrogen at average ration of 0.5%, it is estimated that 32% of the consumed nitrogen was excreted as ammonia-N, about 5% as urea-N and 8% as faeces-N within 24h after feeding.