Potential opportunities and challenges of utilizing brewer's spent grain in sustainable fish feeding within the circular economy.

Alongside growing concern about the environmental impacts of the aquaculture production sector, increasing interest is being directed toward sustainable alternatives to traditional protein sources used in aquafeed, such as fish meal and soybean meal. Among these, brewers' spent grain (BSG), a byproduct of the brewing industry, has recently emerged as an alternative ingredient. BSG is a low-cost, year-round resource that may be well-suited for the circular economy. It contains moderate levels of proteins (15%-27% of dry matter) and appreciable amounts of antioxidant compounds (polyphenols and phenolic acids). Several studies show that BSG can replace up to 50% of traditional protein sources in aquafeed formulations without compromising growth performance. However, BSG has drawbacks, including its high content of antinutritional factors (ANFs) and its relatively low level of essential amino acids. Processing strategies such as hydrolysis and fermentation appear promising for reducing ANFs and enhancing protein availability. Moreover, information on the global impacts of using BSG in aquafeed, either raw or processed, remains limited. A Life Cycle Assessment analysis conducted on two hypothetical diets with 10% or 37% BSG as partial replacements for traditional ingredients reveals that a detailed assessment of environmental impacts across all stages of aquafeed production is essential to support the large-scale adoption of BSG in aquaculture.