Skretting made one of the first advances in the 1980s by introducing extruded feeds. Fat contents could be increased from around 14% to 22–25%. The next increase came with vacuum coating. “This involves a vacuum chamber that follows the drying stage,” explains Jan Jonkers, Feed Production Manager at the Skretting Aquaculture Research Centre (ARC). “The vacuum draws the oil into the feed pellets instead of just coating them.” Introduced in the 1990s, it lifted fat levels above 30%. Maximum fat levels were raised over 40% later that decade when Skretting added an expansion chamber immediately following extrusion. “Reducing pressure opens pores in the pellets to absorb more oil. Alternatively, accurate control of pressure can deliver feeds with sinking characteristics optimised to customer requirements,” adds Jonkers.
High fat feeds brought two new challenges. The first was how to keep the fat in the feed in warm weather. Skretting overcame this challenge through the development of SPAR technology, which involves adding a small proportion of a particular ingredient to the mix. This forms crystals that block the pores and trap the oil inside the pellets.
The second challenge is the sustainability of the oil supply. Aquaculture was expanding rapidly and the far sighted foresaw a potential scarcity of the fish oils being used. Feed companies, research institutes and universities explored options to supplement the fish oils with vegetable oils. “When we first proposed this some people suggested using vegetable oils would lead to mortalities,” comments Dr Alex Obach, Managing Director at Skretting ARC. ARC is one of the participants in the EU-funded RAFOA project. This project had the objective of replacing as much fish oil as possible without compromising the health, welfare and growth performance of the four main European aquaculture species: Atlantic salmon, trout, sea bass and sea bream. Trials with a range of vegetable oils and related adjustments in production methods greatly reduced dependence on fish oils while ensuring the final fish products retain the eating and nutritional qualities consumers expect.
The next sustainability objective was to reduce fishmeal contents. This was achieved by introducing vegetable proteins “For some time 25% fishmeal seemed to be the minimum limit in salmon feed,” says Obach. “We only overcame that hurdle recently by identifying micro-nutrients in fishmeal that proved to be essential to the fish. We found alternative sources of these micro-nutrients. Now, using this MicroBalance™ concept, Skretting is producing grower feeds with much lower fishmeal contents. This means sustainably available fishmeal can be shared across the expanding aquaculture industry and contents minimised when prices peak.”
Other important feed developments include feeds that boost fish immune systems and compensate for the effects of various diseases. The latest hatchery feeds have also boosted the potential of aquaculture.