Why are unsaturated fatty acids particularly abundant in the cellular membranes of antarctic fish?

Antarctic fish species requires an adaptation to cold environment. Living at cold temperature environment would demand certain biological responses such as cutaneous respiration, enlarged blood vessels, and producing greater amounts of fat. Most of these fat are composed of higher phospolipid levels which are primarily due to phosphatidylethanolamine. This phospolipid is responsible for destabilizing cell membranes and make it more fluid thereby allowing unrestricted blood flow. The fatty acid composition of the membrane lipid is important for membrane fluidity, this is mainly attributed to unsaturated fatty acids which are responsible for decreasing the order of membrane lipids thereby decreasing viscosity. At extremely low temperatures, organisms with low concentration of unsaturated fatty acids would freeze cell membranes. That's why antarctic fishes have higher levels of unsaturated fatty acids.