Replacement of marine products with alternative proteins and oils in feeds for Atlantic salmon (Salmo salar L.) : effect on growth, immune function and disease resistance
Creators: name: Bransden, Matthew Paul
Publisher: name: University Of Tasmania
Year: 2023

description: Replacement of marine proteins and oils in feeds for carnivorous fishes such as salmonids has been identified as a key research area. Alternative proteins and oils from vegetable and terrestrial-animal sources can effectively replace marine products, although often growth is the only criteria used to assess their potential. On few occasions has the health of the animal been considered. This research aimed to evaluate what effect alternative protein and oil sources had on growth, immune function and disease resistance when fed to Atlantic salmon, Salmo salar L., parr. Locally available proteins from vegetable and terrestrial-animal sources were initially 'screened' by feeding to salmon to determine any deleterious effects on blood chemistry or immune function. While no significant differences (P&gt; 0.05) were observed, data suggested certain proteins stimulate immunoglobulin production compared to fish meal-fed controls. In a short term experiment, four of these proteins (corn gluten, dehulled lupin, feather meal and poultry meal) were fed to salmon that had been acclimating on a fish meal-based control feed, although the change in protein source did not significantly affect feed consumption or immune function. Growth of salmon fed dehulled lupin, a mixture of dehulled lupin and feather meal, or fish meal were not significantly different in a longer term study, although salmon fed feather meal were found to have significantly reduced (P &lt; 0.05) growth compared to those fed fish meal. Further, no significant differences were recorded in immune function or resistance to Vibrio anguillarum infection. Lysine is usually the first limiting amino acid when alternative protein sources are used in salmon feeds, although the immune response of salmon fed a range of lysine concentrations below or above known requirement was not significantly altered. Three feeds containing canola oil, a mixture of canola and fish oil, or a mixture of canola oil and a marine microheterotroph (Thraustochytrid) meal, did not affect salmon blood chemistry or immune function. Salmon fed the combination of canola and fish oils however had significantly lower (P &lt; 0.05) cumulative mortality after V. anguillarum challenge compared to the remaining feeds. Finally, sunflower oil was used to gradually replace fish oil to alter the dietary omega-3: omega-6 (n-3/n-6) ratio. Although growth and immune function did not differ between feeds, significant differences in cumulative mortality were recorded after challenge with V. anguillarum but they were not correlated to dietary n-3/n-6 ratio. Experiments generally demonstrated alternative protein and oil sources could be used in Atlantic salmon feeds without affecting growth, blood chemistry or immune function. Disease resistance however was shown to be altered when dietary oil or n-3/n-6 ratio was changed, although exact mechanisms for these differences are unclear, and warrant further study.