Gammarid Amphipods as a Potential Source of Omega-3 LC PUFA-Rich Biomass for Functional Ingredients: Nutritional Potential, Controlled Production, and Safety Constraints

New health-promoting food ingredients should combine nutritional functionality, traceable production and sustainable sourcing. Freshwater and brackish gammarid amphipods are usually considered ecological indicators, fish prey or invasive crustaceans, but their biochemical and ecological traits suggest a candidate role as low-trophic aquatic biomass. This narrative review evaluates gammarids primarily as EPA-oriented crustacean biomass and as a potential source of protein, minerals, chitinous material and processing fractions for feed, supplement and functional-food research. Available data indicate meaningful long-chain omega-3 content, especially EPA, but direct evidence for human health effects, bioavailability, clinical efficacy and industrial cultivation remains limited. Wild harvest is unlikely to provide a safe or standardized raw material. The central proposition is, therefore, that gammarid-derived ingredients should be developed through controlled benthic production systems, followed by hygienization, fractionation and safety validation. The most realistic near-term pathway is not direct consumption of whole animals, but standardized feed ingredients, EPA-oriented lipid blends, protein–lipid fractions and supplement-grade materials after regulatory assessment. The review distinguishes established evidence from technological hypotheses and identifies the research required before gammarids can be considered reliable industrial ingredients.