Fish and seafood are one of the most commonly consumed foods and the main raw material of one of the largest industries in the world. Healthy and quality food, such as seafood are above all indispensable foods because of their high nutritional values, but also because they are the source of livelihood of a large part of the population employed in fisheries sector, processing industry, transport and other services. As the human population grows, the need for this resource grows exponentially. With the growth of industrial production, the generation of by-products in the fish processing industry creates a problem. The by-products describe the raw materials generated after the primary product has been produced and they are usually not suitable for direct human consumption. By-products usually lose priority in warehousing and logistics because they have less value than the main product, but their use and valorization is key to conserving marine resources. On the contrary to the general opinion, by-products are not waste, they can be used to obtain fishmeal and fish oil, various forms of protein-rich isolates, bioactive components or eve compost. It can also be used to obtain value-added products such as collagen, gelatin, peptides, enzymes, chitin and chitosan, etc. This paper provides an overview of by-products whose application is possible in the food industry, pharmacy and agronomy, and whose production contributes to the economic and environmental sustainability of the sector.