Well, today I see that Yahoo has a story on the importance of omega 3 fatty acids for us humans. For most of us, the source is fish - salmon, tuna, sardines, etc. I have not seen the data - but, for winter survival, the idea is that fish oil is a fluid. This enhance membrane fluidity. This is often cited as a reason for the role of PUFAs with brain function/development. When the water gets cold, the fish get cold. Therefore, it stands to reason that these fats benefit the animals in cold conditions. If the overall fatty acid profile has too much saturated fat, their fat reserves will solidify in cold water - like tallow in cold water. These PUFAs are important in many other aspects besides the physical properties....
Predatory fish get these fats from the smaller fish they consume. They do not synthesize the long chain PUFAs. The source is from algae and these fats are passed on to algae-eating zooplankton and fish and move up the food chain. Menhaden are excellent sources of the omega 3 PUFAs, because they are fatty fish and about 25% of their fatty acids are the long chain PUFAs. So, in a prepared diet, you need either a significant amount of certain marine algaes, or fish oil or meal (approximately 10% of fish meal is fish oil - as a side note... this is because fish meal is mechanically expressed, so it does not get all the fat out. In solvent-extracted meals - such as soybean meal - there is vurtually no fat left).
