Cod and other deep ocean fish swim in cold water and have core body temperatures

Question

Cod and other deep ocean fish swim in cold water and have core body temperatures of 8-15 ºC. Such fish have high amounts of the polyunsaturated fats 5,8,11,14,17-eicosapentaenoic acid (EPA) and 4,7,10,13,16,19- docosahexaenoic acid (DHA) (docosane = 22 carbon chain). In contrast, mammals have core body temperatures of around 37 ºC (human) to 39 ºC (cows), and have lower amounts of polyunsaturated fats and higher amounts of saturated fats than these fish. What might happen to the fish if they had only saturated fats? What might happen to mammals if they had only unsaturated fats?Give a molecular explanation for the observation that higher percentages of polyunsaturated fats are found in animals with lower core body temperatures.

Explanation / Answer

The degree of saturation and unsaturation of fats is governed by the temperature. Unsaturated fats melt at lower temperatures. The higher is the degree of unsaturation, the lower the temperature should be at which they are viable. Animals must have body fats which are liquid otherwise they would be too stiff to move.

Fishes that live in cold waters contain highly polyunsaturated fats with many double bonds. As the body temperature rises, the fats tend to become saturated and hence would become stiff to move.

In mammals, the degree of saturation is quite high. These saturated fats protect the polyunsaturated fats from oxidation. Else the body would become stiff to move.

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