INFLUENCE OF DIETARY CARBOHYDRATE ON BLOOD-CHEMISTRY, IMMUNITY AND DISEASE RESISTANCE IN ATLANTIC SALMON, SALMO-SALAR L

The influence of dietary carbohydrate (CHO) on blood chemistry, immuni ty and disease resistance was studied in two experiments with Atlantic salmon, Salmo salar L. Moist diets with increasing amounts of digesti ble CHO ranging from 0 to 30% (dry weight) were used. In the first exp eriment with adult (0.5 kg) fish, blood haemoglobin concentration was negatively correlated with increasing dietary CHO level, while serum g lucose and protein did not differ between the groups. Serum cortisol i ncreased linearly in fish fed from 5 to 30% CHO. Serum haemolytic acti vity was negatively correlated with dietary levels of CHO. Humoral imm une responses elicited after vaccination by intraperitoneal injection or by dip immersion with Vibrio salmonicida showed no differences acco rding to diet 10 and 17 weeks post-vaccination. Mortality after challe nge with live Aeromonas salmonicida by intraperitoneal injection was l owest in fish fed 10% CHO. In the second experiment with juvenile Atla ntic salmon (3 g), there were minor differences in body and organ weig hts. Plasma glucose, protein and cholesterol were elevated in fish fed the highest CHO levels. Fish exposed to immersion challenge with diff erent water concentrations of Vibrio anguillarum showed no statistical differences in mortality. The studies indicate that varying dietary l evels of CHO affected immunity and resistance to bacterial infections to a minor extent in Atlantic salmon at low water temperatures during freshwater and seawater stages.