抄録
The influence of stocking density and dietary factors on branchial, urinary and epidermal N losses was assessed in goldfish. Water, skin mucus and urine samples were collected for analyses of ammonia, urea and free amino acids (FAA). Results indicated that postprandial ammonia (NH4-N) excretion rates per unit body weight were significantly affected by stocking density. Stocking density also had a significant effect on urea excretion and FAA concentrations in the branchial plus urinary excreta. No correlation was detected between dietary amino acid pattern and the FAA profiles in the mucus. The concentration of taurine was high (>40 μmole/g dry matter) in mucus. In the urine of unfed fish, total amino acid levels (>2 mmole/ι) were ten-fold higher than in fed fish. The concentration of taurine in the urine of unfed fish represented > 95% of total FAA. Owing to the high concentrations of taurine in skin mucus and urine and the variations found, the effects of waterborne taurine on swimming orientation of goldfish were tested and compared to those of alanine, at three concentrations (10-6, 10-5, 10-4M). Unlike alanine, highest attraction response was observed for taurine even at the lowest concentration tested.
