CommentaryFish silage hydrolysates: Not only a feed nutrient, but also a useful feed additive

•Use of formic acid is an excellent way of preserving fish by-products.•The acid protein hydrolysate obtained is a useful feed ingredient.•The free amino acid and peptides may contribute to improved growth.•The formic acid in the hydrolysate could function as a growth promotor.•May be particularly relevant under unfavourable microbiological conditions.

BackgroundProcessing of fish and shellfish may result in substantial amounts of by-products and unless they can be used as food, the most realistic option in most cases is the production of preserved feed nutrients. If large volumes are available, reduction to fishmeal and fish oil is the preferred technology. However, fresh by-products are most often available in insufficient quantities to justify production of fishmeal. Preservation by acid silage is, however, a simple and inexpensive alternative.Scope and approachThe purpose of this paper is to highlight that silage preservation of by-products using formic acid produces a protein hydrolysate that may function as a useful feed additive and not only an important feed nutrient. The fast growing global aquaculture industry is particularly in need of high quality feed nutrients and the focus in this paper is therefore on including acid protein hydrolysate in diets for fish and shellfish.Key findings and conclusionsThe proteins in acid silage are largely hydrolysed to free amino acids and short-chain peptides. Studies have shown that moderate amounts of protein hydrolysate may successfully be included in fish feed and in some cases this leads to improved performance. In addition, the formic acid in the hydrolysate may contribute to the growth and well-being of fish, in particular under unfavourable microbiological conditions. This may encourage fish processors to preserve by-products using acid silage and feed producers to incorporate the products in the feed.