| Abstract: |
Five experiments were carried out during the work with this thesis in order to: 1) determine thedietary requirement of manganese and magnesium for Atlantic salmon, 2) study the effect ofdietary magnesium on immune response and osmoregulation of Atlantic salmon, 3) study theeffect of fasting on Atlantic salmon smolts with emphasis on mineral status and 4) to collectbase line information on whole body concentration of some essential elements for Nile tilapiaand the level of contamination by some heavy metals in market size fish.Exp.l. This experiment was conducted to establish the dietary manganese requirement inAtlantic salmon (Salmo salar) during start feeding. Atlantic salmon fly with initial weight of0.18 g were divided in six triplicate groups (900 fish each) fed casein-gelatine diet (containing1.1 Mu kg-I) supplemented with either 0, 3, 6, 9, 12 or 24 mg Mn kg-1 as MnS04 for 12weeks. Growth was recorded. every four weeks. Concentrations of Mu , Ca, P, Zn and Fewere measured in whole fish. Superoxide dismutase (SOD) activity was also measured in liversafter 12 weeks offeeding. ’.Exp. II. This experiment was undertaken to establish the magnesium requirement in youngAtlantic salmon (Salmo sa/ar) in sea water treated fresh water. Parr with initial weight of 8 g,were divided in six triplicate groups (200 fish each) in water containing 54 mg Mg L-l and feda basal, casein-gelatine diet (containing 200 mg Mg kg-I) in an initial period of three weeks.Thereafter the fish were fed diets supplemented with either 0, 100, 200, 300, 400 or 500 mgMg kg-l as MgS04 for 12 weeks. Growth and feed efficiency were recorded every fourweeks. Concentrations ofMg and other divalent cations (Ca and Zn) were measured in wholefish, serum and vertebrae. Sodium concentration in vertebrae was also measured.Exp. ill The influence of dietary magnesium (Mg) on immune response and osmoregulationwas studied in Atlantic salmon (Salmo salar) parr (mean weight of 50 g) reared in watercontaining 54 mg Mg/L. This experiment was a continuation of Experiment 11, where thesame experimental set-up was used. Number of the fish in all dietary groups were reduced to
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