Fish fed with a fibre-rich diet produce stable faecal pellets that are easy to remove.
Traditionally, fish feeds for salmon and other carnivorous fish are based on fish meal and fish oil, obtained from wild fish. To be less dependent on wild fish, plant ingredients are included in fish feeds. However, carnivorous fish are not particularly efficient in digesting plant-based feed. Therefore such ‘vegetarian’ pellets can easily lead to more waste and thus more pollution of water.
To make fish feeds which are less polluting, AFI studies the mechanisms involved in the amount and the stability of faeces produced. This research subject is part of the EU-programme ARRAINA, whose consortium consists of ten research institutes and thirteen companies that are developing alternative fish feeds.
We have created plant-based fish feeds for trout in such a way that the faecal pellets hardly cause any pollution. In an experiment with rainbow trout, we tested two types of diets: one with a high amount of fibres and one with a high amount of starch. Although the first one led to more waste, it resulted in cleaner water. The faecal pellets produced by the fish on the fibre-rich diet were more stable and much easier to remove from the water than the more instable waste from the starch-rich diet. This shows that a proper diet can lead to less pollution.
We study the potential of using enzymes in plant-based fish feeds, as they also may improve the digestibility. And, apart from the issue of waste production, AFI studies the impact of alternative fish feeds on fish health and nutrient requirements. The questions addressed are: how do plant ingredients alter the micro flora in the gut and the gut barrier function? And do fish fed plant-based diets have other mineral requirements, like phosphor?
For more information please visit the ARRAINA website.
For more AFI projects, please see link.
For the ARRAINA Technical Booklet, please see link