EFFECT OF FEEDING ON NITROGEN-EXCRETION OF JAPANESE FLOUNDER PARALICHTHYS-OLIVACEUS

Measurements of the rate of nitrogen excretion were carried out with fed and starved Japanese flounder of 163 to 575 g in body weight at 20-degrees-C. Ammonia-N and urea-N excretion of the starved fish were 0.20 +/- 0.05 mg-N/100 g/h and 0.04 +/- 0.02 mg-N/100 g/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 36 h, 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 12-24 h 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 24 h after feeding.