Nitrogenous Excretion of Juvenile and Young Japanese Flounder

Abstract

Measurements of the rate of nitrogenous excretion were carried out on fed and starved Japanese flounder of 1.5 to 6.5g (juvenile), and 15 to 91g (young) in body weight at 20°C. Ammonia-N and urea-N excretion of the starved juvenile flounder were 0.76±0.20mg-N and 0.09±0.03mg-N/100g/h, and those of the young flounder were 0.23±0.05mg-N and 0.07±0.03mg-N/100g/h, respectively. Immediately after feeding, the rates of ammonia-N excretion per hour of both juvenile and young flounder became 2 to 3 times higher than those of the starved fish, and these elevated rates continued for more than 12h. 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 juvenile and young Japanese flounder fed on a pelleted diet containing 7.5% nitrogen at average rations of 3.0 and 1.3%, respectively, it is estimated that 23 and 21% of the consumed nitrogen was excreted as ammonia-N, 3 and 4% as urea-N, respectively, and about 13% as faeces-N within 24h after feeding.