How do cold blooded fish stay warm in the ocean?
Those deep ocean waters can get pretty cold. For swordfish, for example, temperatures can get as cold as 38 degrees Fahrenheit.
Over the course of evolution, the swordfish have developed a special heating organ that enables them to keep their brain and eyes about 15 to 30 degrees warmer than the water around you.
Heating is physiologically expensive, and of more than 25,000 species of bony fish, only about 22 species have this ability.
A study by Australian scientists has helped explain why swordfish need to keep their tennis-ball-sized eyes warm. Scientists removed the retinas from some freshly caught swordfish and studied the speed of the retinal response to flickering light over a range of temperatures. It turned out that the warmer the retina, the faster the speed of the response.
Heating their retinas enables swordfish to capture flickers of light more effectively which, in turn, enables them to better see their fast-moving prey. Now that's an amazing adaptation!