Substantial waste is produced by the commercial fishing sector, as parts like viscera, skeletal remains, scales, and skin are frequently treated as refuse, causing both ecological strain and the loss of valuable resources. Yet, there is a growing movement to view these leftovers as untapped assets. Through modern bioprocessing techniques, this discarded matter can be converted into premium goods, including medicines, health supplements, renewable energy, and eco-friendly packaging. By embracing this circular approach, the seafood industry can better align with international sustainability targets. This article investigates the multifaceted potential of these marine by-products, the framework of the circular economy, and the systemic hurdles that remain in achieving a fully sustainable supply chain.