Worm-it: converting organic wastes into sustainable fish feed by using aquatic worms

Due to overfishing and the use of one-third of wild fish catches for feeding farmed fish and livestock, there is a strong need for alternative sources of suitable proteins and lipids in fish feeds. Small freshwater worms of the species Lumbriculus variegatus can be such a source based on their high protein content, variable lipid content and amino acid pattern. In addition, their production can be combined with waste reduction, as they can be grown on safe organic wastes. In this article, it was investigated whether fatty acid (FA) profile of the worms changed with feed source. Profiles of worms grown on different feeds were highly similar, but also reflected profiles of feeds. Data suggest that the worms are capable of poly-unsaturated fatty acids bioaccumulation. The worms converted different organic wastes (fish faeces and food industry sludges) with an efficient feed conversion ratio of ~1.8 (dry to wet weight) resulting in a theoretical production of 0.1-0.14 kg of fish per kg of waste. Worm composition resembles that of other live feeds and the biomass contains important FAs. Safety of organic non-feed waste streams for worm production should be further evaluated.