Medium size (3000 d > Mw > 500 d) peptides from a hydrolysate of emptied stomachs from Atlantic cod (Gadus morhua) were fractionated on an S-Sepharose cation exchange chromatography column. Four distinctly separated acid peptide fractions were used in in vitro stimulatory experiments 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 μg/ml. The stimulation was equally good, and in most cases better than the stimulation achieved with similar concentrations of lipopolysaccharides from the fish pathogen Aeromonas salmonicida. Visual inspection and pictures of peptide stimulated cells showed strongly enhanced vacuolisation and formation of long stretched out pseudopodes after 7 days of incubation. Acid peptide fractions from fish protein hydrolysate may be useful as adjuvants in fish vaccine and as an immune stimulant in fish feed.

Atlantic salmon fry were reared ad libitum on a commercial fish feed supplemented with 10% cod muscle protein (A), 10% hydrolyzed cod muscle protein (B) or 10% of a hydrolysate based culture of lactic acid bacteria isolated from salmon intestines. The fry grew well, and equally so, on each of the three diets (specific growth rate, 2.5% day(-1)), Very low numbers of intestinal bacteria were detected in fish given diets A and B, whereas a considerable colonization of the intestine by lactic acid bacteria was achieved in fish given diet C.After 5 weeks of feeding, the fish were challenged with cohabitants infected with Aeromonas salmonicida. Four weeks after infection, a cumulative mortality between 42 acid 75% was recorded in the different tanks. Unexpectedly the highest mortality was observed with fish given the diet containing lactic acid bacteria, whereas no significant difference was observed between fish given feed supplemented with cod muscle protein and hydrolyzed cod muscle protein.

A crude lysozyme preparation was recovered in waste from the scallop processing industry. Lysozyme was then purified 229-fold in preparative scale by chromatography on S Sepharose and Blue Sepharose. Further purification on Sephacryl S-200 resulted in a lysozyme preparation with a specific activity of 64,000 units/mg protein. The apparent molecular mass of the partially purified lysozyme was 10 kDa as judged by gel filtration. Optimum pH for lysis of Micrococus luteus under the present conditions was 5.2. The enzyme was very active at low temperatures. At 4 degrees C the scallop viscera lysozyme exhibits about 55% of the activity measured at 37 degrees C.