Feed for Atlantic salmon in RAS: Why consider a dedicated RAS feed?
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by Dr Robert Tillner, Product Manager, Aller Aqua Group, Denmark
eed is what makes Atlantic salmon grow in RAS. Together with a decent Feed Conversion Ratio (FCR), an article about RAS feed for Atlantic salmon could basically stop here‌ Or not? Why not stick to a regular grower feed for Atlantic salmon and save money, especially when the feed costs account for such a large part of the overall costs? Indeed, the choice of feed has a major impact on the growth of the fish, the efficiency of the RAS and the economic output of the farm. First of all, introducing highly palatable and digestible feeds with a high uptake limits the number of wasted feed pellets to a minimum, reducing the need to filter out uneaten and decomposing feed pellets. Additionally, providing all required nutrients in terms of amino acids, fatty acids, vitamins and minerals lays the foundation for growth and health of the fish. Their optimal combination will accelerate the production cycle and improve the output of the RAS. This is achieved by selecting raw materials of the highest quality and by basing the composition of the feed on the digestible nutrient content of each raw material batch to secure stable feed quality. Special attention is paid to the quality of the pellets. It is important to eliminate dust and broken pellets that might otherwise put pressure on the filtration units. Also, functional ingredients ensure the health and welfare of the fast-growing
fish. Growth and health are, however not the only factors to play an important role in RAS, as feed efficiency will also to a large extent influence costs and revenue.
Four percent increase in FCR
Growth trials with Atlantic salmon at Aller Aqua Research have revealed an improvement in FCR by four percent when comparing Aller Flow to a dedicated RAS feed from a competitor. In commercial RAS with several thousand tonnes of fish, these four percent equal a massive increase in revenue. For the trial, the efficient use of nutrients was further reflected in higher slaughter and fillet yields of Atlantic salmon against a competing RAS feed. Moreover, every digit improved in feed conversion means fewer fish faeces and metabolites to be handled by energy-consuming filtration units in RAS, improving both their efficiency and long-term dimensioning. Therefore, paying special attention to the impact of the feed on the production system whilst keeping the fish in focus is key. In this regard, the structure of the fish faeces plays an important role since this determines the effective removal by mechanical filtration. The secret is binding smaller faeces particles to bigger ones, establishing a firm structure while keeping them light enough to be easily transported through the system. This prevents faeces particles from breaking down into smaller and smaller particles, increasing water turbidity and the workload of the filtration units. A positive side effect is lowered oxygen consumption due to a
20 | August 2020 - International Aquafeed