Seaweed-fed black soldier fly (Hermetia illucens) larvae as feed for salmon aquaculture: assessing the risks of pathogen transfer

Sustainable ingredients for animal feed are becoming scarcer. Insects have emerged as a promising protein and lipid ingredient for fish feed, and black soldier fly (BSF; Hermetia illucens) larvae in particular have great potential to efficiently convert organic matter into high value protein and fat. Seaweeds are a sustainable source of organic matter and complex carbohydrates, but can also provide marine long chain polyunsaturated fatty acids for fly larvae, and therefore could offer a commercially attractive alternative to traditional aquafeeds. However, pathogenic bacteria and faecal indicator organisms (FIOs) readily attach to seaweeds, therefore before this novel BSF larvae feed ingredient is advocated, microbiological risk assessments are warranted to ensure animal and public health protection from farm-to-fork. In this study, screening of raw materials and finished products during formulation of experimental insect meal fish feed was undertaken to evaluate the potential for the introduction of selected bacterial pathogens and FIOs via seaweed substrate to BSF larvae, and subsequent survival during multiple manufacturing processing stages. Processed seaweed powder was found to be a microbiologically safe feed substrate for BSF larvae. Low levels of FIOs were associated with larvae at the point of harvest, although larvae meal and extracted lipids were free of FIOs immediately after processing. During handling, distribution and storage the larvae meal and other externally sourced raw feed ingredients for larvae rearing and feed pellet formation became contaminated with FIOs and Listeria spp. FIOs were also present, albeit at very low levels, in the finished feed pellets. Processing treatments provided effective decontamination, and FIO and pathogen concentrations in finished products never exceeded microbiological quality standards for insect processed animal proteins. Microbiological contamination of raw materials and finished products during packaging and distribution, or originating from production environments, were identified as critical control points, requiring assessment to ensure good hygiene practices.