Seaweeds constitute an essential part of the marine flora in the marine ecosystem. In response to the stressful conditions in which they exist in the marine ecosystem, they defend themselves by producing secondary metabolites with biological effects. One of the secondary metabolites in seaweeds, polyphenolic compounds, exhibit antioxidative and antibacterial properties in many fish and fish-based products. Preservatives improve the shelf life of food products by acting as antioxidants, antimicrobials, or pH regulators. Due to the potential health risks associated with synthetic preservatives, natural preservatives are now chosen to improve the quality, safety, and stability of food products. Therefore, seaweed extracts high in phenolic compounds have the potential as a natural fish preservative.