Photo: VCG

For fish inhabiting the immense darkness of the deep sea, being ultra-black offers great camouflage in a fish-eat-fish world. Scientists studying some of these exotic creatures now have unraveled the secret behind their extreme color.

These fish - like the fangtooth, the Pacific blackdragon, the anglerfish and the black swallower - have modified the shape, size and packing of the pigment in their skin to the point that it reflects less than 0.5% of light that hits it, researchers said on Thursday.

Very little sunlight penetrates more than 650 feet (200 meters) below the ocean's surface. Some of these fish reside three miles (5,000 meters) deep.

At such depths, bioluminescence - light emission by living organisms - is the only light source. Some of the ultra-black fish have bioluminescent lures on their bodies to coax prey close enough to be eaten.