Growth and survival of Atlantic salmon (Salmo salar) fry given diets supplemented with fish protein hydrolysate and lactic acid bacteria during a challenge trial with Aeromonas salmonicida

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.