Why the animals of colder region and fishes of cold water have thicker layer of subcutaneous fat?

Animals in colder regions and cold-water fish have thicker layers of subcutaneous fat to provide insulation against the cold, helping to maintain their body temperature. This fat layer acts as both a thermal barrier and an energy reserve, which is crucial for survival in harsh environments where food may be scarce. Additionally, the buoyancy provided by fat helps fish maintain their position in water without expending excessive energy. Overall, these adaptations are essential for their survival in extreme cold conditions.