Fish Sludge as Feed in Circular Bioproduction: Overview of Biological and Chemical Hazards in Fish Sludge and Their Potential Fate via Ingestion by Invertebrates

ABSTRACT Aquaculture farming discharges large volumes of fish sludge, consisting of particulate organic matter from feed spill and feces. Fish sludge from land‐based salmonid aquaculture systems can potentially be used to feed low‐trophic species such as marine polychaetes and insects. Further use of these invertebrates as feed may provide a more sustainable feed chain. However, food security must not compromise feed or food safety. The use of fish sludge as feed is currently not permitted in the European Union (EU). A regulatory assessment that considers the integration of fish sludge in the circular bioeconomy requires knowledge of the potential chemical and biological risks involved. This review has compiled data from existing literature on the occurrence of chemical and biological hazards, as well as the physical properties of fish sludge. The potential risks along this feed chain, from fish sludge to novel feed ingredient production, are discussed in light of the EU regulatory framework. Within the available, but scarce, literature on biological hazards in fish sludge, there is no clear evidence that fish sludge is unsafe for use as a feed material for invertebrates if treatment criteria established in the EU regulations are followed. Scarcity implies a level of uncertainty, but not necessary of risk. For the chemical hazards, some elements are of concern and may exceed regulatory limits, and there are limited data on the occurrence of organic pollutants. This review highlights considerable knowledge gaps concerning the use of fish sludge in a circular feed and food system.