DIFFERENCES IN DIGESTION AND ABSORPTION OF DIETARY-PROTEIN IN ATLANTIC SALMON (SALMO-SALAR) WITH GENETICALLY DIFFERENT TRYPSIN ISOZYMES

Digestion and absorption of dietary protein were studied through facil itation of amino acid in the plasma and white muscle after a single fe eding. The comparison was made between Atlantic salmon with and withou t trypsin isozyme TRP-2()92. Higher absorption of dietary protein was associated with the presence of the isozyme, as the post-prandial tot al levels of free amino acids (FAA) in both plasma and white muscle we re significantly higher in salmon with the isozyme than those in salmo n without it. Higher digestion rate of the dietary protein in salmon c arrying the isozyme was indicated by faster elevation of essential FAA in the plasma and of overall FAA in their white muscle. Other indicat ions which suggest differences in nitrogen metabolism between salmon w ith and without the isozyme were the observations of significant diffe rences in (a) the levels of lysine, hydroxyproline, alanine, aspartic acid, beta-alanine, threonine, valine and a nitrogen-containing compou nd taurine in plasma, and (b) the levels of alanine, glutamic acid, gl ycine and anserine in white muscle. Trypsin activity in the pyloric ca eca showed less response to feeding than that in the intestine, but it may have consequence for growth as its activity was significantly hig her in growing fish than in non-growing fish.