Lipids and fatty acids are major organic components of fish, playing critical roles in energy metabolism, growth, reproduction, and movement. Fish lipids are particularly rich in ω-3 long-chain polyunsaturated fatty acids (n-3 HUFA), which are vital for fish and human nutrition. This review summarizes the biochemistry, metabolism, and functions of fatty acids and lipids in fish, emphasizing their roles in natural and farmed environments. It highlights the importance of molecular technologies in advancing understanding of fish lipid metabolism. Key areas include digestion, absorption, transport, biosynthesis, catabolism, and functions such as energy production, membrane structure, eicosanoids, and lipid homeostasis regulation. Fish lipids are composed of neutral lipids like triacylglycerols and polar lipids like phosphoglycerides. Lipid digestion in fish is similar to mammals, with bile salt-activated lipases playing a key role. Lipids are absorbed and transported via lipoproteins, with variations in lipid composition and transport mechanisms among fish species. Intracellular transport of fatty acids is facilitated by fatty acid-binding proteins. Lipogenesis in fish involves the synthesis of saturated fatty acids, while catabolism includes fatty acid breakdown for energy. The review also discusses the importance of lipid metabolism in fish nutrition and the application of molecular techniques to further study these processes.Lipids and fatty acids are major organic components of fish, playing critical roles in energy metabolism, growth, reproduction, and movement. Fish lipids are particularly rich in ω-3 long-chain polyunsaturated fatty acids (n-3 HUFA), which are vital for fish and human nutrition. This review summarizes the biochemistry, metabolism, and functions of fatty acids and lipids in fish, emphasizing their roles in natural and farmed environments. It highlights the importance of molecular technologies in advancing understanding of fish lipid metabolism. Key areas include digestion, absorption, transport, biosynthesis, catabolism, and functions such as energy production, membrane structure, eicosanoids, and lipid homeostasis regulation. Fish lipids are composed of neutral lipids like triacylglycerols and polar lipids like phosphoglycerides. Lipid digestion in fish is similar to mammals, with bile salt-activated lipases playing a key role. Lipids are absorbed and transported via lipoproteins, with variations in lipid composition and transport mechanisms among fish species. Intracellular transport of fatty acids is facilitated by fatty acid-binding proteins. Lipogenesis in fish involves the synthesis of saturated fatty acids, while catabolism includes fatty acid breakdown for energy. The review also discusses the importance of lipid metabolism in fish nutrition and the application of molecular techniques to further study these processes.