POOR UTILIZATION OF DIETARY FREE AMINO-ACIDS BY WHITE STURGEON

Three separate experiments were conducted to investigate the utilizati on of dietary free amino acids by white sturgeon, Acipenser transmonta nus. In the first experiment, sturgeon were fed for 8 weeks with isoen ergetic and isonitrogenous diets containing either intact protein, an amino acid mixture, or a neutralized amino acid mixture of similar com position. Sturgeon fed the two amino acid diets grew significantly (p < 0.05) less, mainly because of reduced feed intake. In the second exp eriment, postprandial changes in plasma free amino acids of sturgeon f orce-fed the above diets were monitored at 2, 4, 6, 8, 12, and 24 h. T otal plasma amino acids in sturgeon force-fed the intact protein diet showed a gradual increase and reached peak levels at 8 h. In contrast, plasma amino acids of fish force-fed the amino acid diets showed a ra pid increase and reached maximal levels at 2 h. In the third experimen t, free amino acid excretion in the urine of sturgeon force-fed the th ree diets was monitored at 4, 8, 12, 16, 20, and 24 h. In all dietary groups, peak excretion of indispensable amino acids was detected at 8 h after feeding but with significantly higher levels from fish force-f ed the amino acid diets. Sturgeon force-fed the neutralized amino acid diet excreted 35% less amino acids compared to fish force-fed the non -neutralized diet. Sturgeon force-fed the intact protein diet excreted significantly higher amounts of ammonia. Under amino acid feeding con ditions, sturgeon excreted more amino acids in its urine, but the urin ary excretion of amino acids was not a major route in dealing with the rapid absorption of dietary free amino acids.