Irish macroalgae as feed supplements in farmed Atlantic salmon (Salmo salar): Safety, viability, quality, and economic feasibility
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The increase in global food demand coupled with competition for arable land use has led to substantial growth in the aquaculture industry, and in particular, finfish farming. Consequently, farming of species such as salmon has placed increasing pressures on wild fish stocks to supply the fish meal demand for feeding these farmed fish. Partial replacement of fishmeal through the use of plant-derivative meals (e.g. cereals, soybean) has resulted in a reduction in the proportion of fish meal used in finfish diets. However, the demand for plant meals can add further pressure on arable land, finite fertilisers (e.g. phosphorous), and freshwater resources. Seaweeds have gained focus as a sustainable feed ingredient due to their limited land-based resources requirement. This comprehensive study will examine commercially important seaweeds found in Ireland for their viability in farmed Atlantic salmon (Salmo salar) diets. An initial appraisal of Irish green seaweed blooms (Ulva spp.) showed that many of the collection sites were within national and international safety limits for toxic metals. The testing of U. rigida and Palmaria palmata in separate salmon feeding experiments revealed that up to 15% was tolerated by the salmon with no detrimental effect on growth performance, blood parameters, and immunological status. Further analysis was carried out on the quality of the salmon fillet muscle and the accumulation of toxic metals in the fish tissue revealing no negative influence. This research showed the potential of seaweeds as a feed supplement; however, like terrestrial plant meals, there is a need for further processing (i.e. to reduce carbohydrate content and release complex nutrients) to enhance digestibility, functionality, and overall economic competitiveness. The development of a sustainable marine-based product for inclusion in farmed finfish diets will have substantial benefits for both the environment and for generating wealth and jobs for coastal communities.