by Dr Robert Tillner, Product Manager, Aller Aqua Group, Denmark

 

Feed 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 more effective biological filtration, leaving increased levels of precious oxygen to be used by the fish for growth. Figures 1 and 2 show that the faeces structure and faeces harvest in a controlled setup at Aller Aqua Research, has significantly improved for Aller Flow, compared to a commercial RAS feed from a competitor.

An often-overlooked effect is the presence of non-protein nitrogen in raw materials and different batches of the same raw material. This non-protein nitrogen cannot be utilized by the fish for growth but goes directly into the biofilter for nitrification. Studies at Aller Aqua Research have shown a possible reduction of up to 14 percent of non-protein nitrogen when comparing different raw material batches. Checking for non-protein nitrogen in raw materials in RAS feed increases the efficiency of the biofilter and reduces unwanted fluctuations due to varying levels of non-protein nitrogen in different feed batches.

Coming back to the initial question, producers of Atlantic salmon in RAS should carefully choose the right feed for this highly sophisticated production system, focusing on feed revenue instead of feed costs. Keeping the above-mentioned aspects in focus, Aller Aqua introduces its dedicated feed for Atlantic salmon in RAS, Aller Flow as the newest member of the recently launched PowerRAS concept. Its development profits from research efforts of feeds for RAS during the past years at Aller Aqua R&D, focusing on pellet quality, feed efficiency and water quality.

Aller Flow contains no animal by-products and is available in 3 and 4.5mm sizes for Atlantic salmon farmers in RAS. For further information please contact Dr Robert Tillner, Product Manager at rt@aller-aqua.com or +49 159 018 419 89.

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