ISOLATION OF ACID PEPTIDE FRACTIONS FROM A FISH-PROTEIN HYDROLYSATE WITH STRONG STIMULATORY EFFECT ON ATLANTIC SALMON (SALMO-SALAR) HEAD KIDNEY LEUKOCYTES

Medium size (3000 d > M(w) > 500 d) peptides from a hydrolysate of emp tied stomachs from Atlantic cod (Gadus morhua) were fractionated on an S-Sepharose cation exchange chromatography column. Four distinctly se parated acid peptide fractions were used in in vitro stimulatory exper iments with head kidney leucocytes from Atlantic salmon (Salmo salar). All four acid peptide fractions promoted strongly elevated oxidative burst reactions in the leucocytes after 2 and 7 days of incubation at concentrations from 1 to 25 mu g/ml. The stimulation was equally good, and in most cases better than the stimulation achieved with similar c oncentrations of lipopolysaccharides from the fish pathogen Aeromonas salmonicida. Visual inspection and pictures of peptide stimulated cell s showed strongly enhanced vacuolisation and formation of long stretch ed out pseudopodes after 7 days of incubation. Acid peptide fractions from fish protein hydrolysate may be useful as adjuvants in fish vacci ne and as an immune stimulant in fish feed.