AUTHOR=Carr Ian , Glencross Brett , Santigosa Ester TITLE=The importance of essential fatty acids and their ratios in aquafeeds to enhance salmonid production, welfare, and human health JOURNAL=Frontiers in Animal Science VOLUME=Volume 4 - 2023 YEAR=2023 URL=https://www.frontiersin.org/journals/animal-science/articles/10.3389/fanim.2023.1147081 DOI=10.3389/fanim.2023.1147081 ISSN=2673-6225 ABSTRACT=Long chain polyunsaturated fatty acids (LC-PUFA), namely those from omega-3 (n-3) and omega-6 (n-6) families, are paramount for fish and human nutrition. Some of these biomolecules cannot be synthesized de novo and must be acquired through the diet, being termed essential fatty acids (EFA). Fish requirements for EFA have traditionally been met through the incorporation of fish oil (FO) in the formulation of aquafeeds. However, with limited supply of FO the aquaculture industry is searching for additional sustainable sources of EFA. This has significantly shifted the type of ingredients used in aquafeed formulation, namely vegetable oils deprived in n-3, often resulting in unbalanced levels and ratios of EFA. Such imbalances can negatively affect fish performance and welfare, as well as the levels of health promoting omega-3 LC-PUFA present in fish fillets. Given the relevance that salmonid aquaculture plays in global fish production (principally Atlantic salmon, Salmo salar), as well as its growing role as a source of dietary health promoting omega-3 LC-PUFA for humans, the present review summarizes the scientific knowledge available to date on the dietary requirements for EFA in salmonids and humans. We discuss the implications of using unbalanced aquafeed formulations upon fish performance and welfare, as well as follow on consequences for human nutrition, along with current efforts to replace FO by alternative ingredients that can safeguard high-quality salmonid products for human consumption.