The feasibility of underutilised biomass streams for the production of insect-based feed ingredients: The case for whisky by-products and Scottish farmed salmon

In recent years, insect meal has received considerable attention as an alternative ingredient for aquaculture feeds. When insects are reared on underutilised biomass streams, the resulting meal can potentially offer a reduced environmental impact compared to fishmeal and soybean meal. However, due to legislative restrictions, insects are commonly reared on materials that are also suitable to feed farm animals directly, including farmed fish. This practice compromises both the environmental and economic sustainability of insects as feed. For insect rearing to realise its potential and upcycle organic waste back into the food chain, substrates should thus consist of underutilised biomass. The aim of this study was to identify and assess the feasibility of underutilised biomass streams in Scotland for producing insect-based salmon feed ingredients, specifically defatted meal and oil from black soldier fly (BSF) larvae. Key information was collected on the most important biomass streams in Scotland, including their origin, available volumes, current utilisation, composition, geographic distribution, and legal status for insect rearing. To estimate the performance and body composition of BSF larvae reared on these biomass streams, a literature review was performed. The obtained data were then used to model the feasibility of different biomass streams as substrates for larvae meal and oil production. Based on the results, two whisky by-products are identified as the most promising biomass streams for BSF larvae rearing in Scotland, namely draff and pot ale. Draff is increasingly burned for bioenergy and most pot ale remains unused. It is estimated that 8.500 tonnes of larvae meal and 3.800 tonnes of larvae oil could potentially be produced from the largest geographical concentration of these distillery by-products in Scotland. This would make a considerable contribution to the raw material supply for Scottish salmon feed, whilst generating added value and upcycling otherwise wasted nutrients. However, more studies are required to examine and optimise the actual suitability and feasibility of whisky by-products as substrate for rearing BSF larvae