Caldicellulosiruptor saccharolyticus as a potential fish feed

Every second fish consumed by humans today is produced in aquaculture, and the main protein source in the fish feed is fishmeal. For every farmed salmonid, 1.8 fish are used in that fish’s feed. Hence, there is a great need of alternative protein sources to make aquaculture sustainable. The bacterium Caldicellulosiruptor saccharolyticus, used experimentally for hydrogen production, has a protein content almost as high as fishmeal and might be a good alternative. After the hydrogen production, C. saccharolyticus could be utilized as bacteria meal, which also would increase the value in the hydrogen production. This project examined the nutritional ability and environmental profitability of partly replacing fishmeal with bacteria meal made of C. saccharolyticus in fish feed for salmonids (i.e. different species in the Salmonidae family) in three perspectives. Firstly, the amino acid profiles of a hypothetical feed containing different amounts of C. saccharolyticus were theoretically compared with a reference feed and the requirements for different salmonids. It showed that it might be possible to replace fishmeal with up to 30% of bacteria meal for salmonids, but feeding trials are needed to determine the real value. Secondly, the potential toxicity of residues in the bacteria from the hydrogen production was considered, but only negative results were received. Finally, an environmental investigation was made, comparing the carbon footprint for fishmeal production and a hypothetical bacteria meal production process. The carbon footprint for bacteria meal could be reduced to 15% of the footprint for fishmeal, and a feed based on 30% C. saccharolyticus could lower the feed’s carbon footprint by 20%.