Manganese requirement of Atlantic salmon (Salmo salar) fry

Abstract

The present experiment was undertaken to establish the dietary manganese (Mn) requirement in Atlantic salmon fry and to examine the effect of Mn intake and status on disease resistance. Salmon fry were divided into six triplicate groups and fed a casein/gelatine diet (containing 1.1 mg Mn/kg) supplemented with 0, 3, 6, 9, 12 or 24 mg Mn/kg (as MnSO4) for 12 weeks. Growth, mortality and whole body Mn were recorded every 4 weeks. Concentrations of calcium, phosphorus, zinc and iron in whole fish and total hepatic superoxide dismutase activity were measured after 12 weeks of feeding. After the feeding experiment, the fish were challenged with Vibrio anguillarum. Dietary Mn levels did not affect growth and mortality. Whole body Mn concentration responded readily to dietary Mn supplementation and reached a plateau in fish receiving diets supplemented with more than 6 mg Mn/kg. Regression analysis showed that whole body Mn concentration was maintained at dietary Mn concentrations of 7.5-10.5 mg/kg dry feed. Supplementation of only 3 mg Mn/kg diet was enough to saturate the total hepatic superoxide dismutase activity. The dietary Mn levels did not affect the mortality after bacterial bath challenge with a virulent strain of V. anguillarum. In conclusion, a minimum Mn requirement of 7.5-10.5 mg/kg dry diet was needed to maintain Mn status in Atlantic salmon during start feeding.