From waste to wealth: functional and bioactive compounds recovered from fish by-products

Increasing fish consumption has generated huge volumes of processing residues (heads, bones, skin, viscera, and frames, etc.), often discarded as waste. These by-products are rich in proteins, peptides, omega-3 fatty acids, collagen, enzymes, minerals and other bioactives. Intensive research now shows that compounds recovered from fish waste exhibit potent functional and biological activities (antioxidant, antimicrobial, anti-inflammatory, antihypertensive, and antidiabetic, etc.). Accordingly, valorization of fish by-products is an emerging bioeconomy strategy: for example, protein hydrolysates are used as food additives, fish collagen/gelatin as nutraceutical supplements, gelatin as edible films or biomaterials, and fish oils as concentrated omega-3 nutraceuticals. This review surveys fish by-product streams, extraction methods, and major bioactive constituents, focusing on their functional properties and applications in food, nutraceutical and pharmaceutical industries. Finally, we discuss challenges (e.g., variability, contaminant risk, processing costs) and future prospects (green technologies, integrated biorefinery) for sustainable valorization of marine residues.