OCEAN ANIMALS
MESOPELAGIC ZONE

In the mesopelagic zone, the temperature is more constant. Light intensity is low, decreasing to almost zero at the bottom of the zone, and blue light predominates.

Many mesopelagic fish have mirror-like sides. These reflect only the available light, and if there is no light, they appear black. In this zone, prey is scarce. Deep sea fish are less streamlined than those of the upper waters. They have larger eyes, a darker, more shiny body and light organs along their sides and belly. Many of the fishes living in this zone have light-producing organs called photophores. Some of the small deep-sea sharks have tiny light organs all over the skin so that the whole fish glows with a greenish light. Lantern fish are very common in this zone. These small fish migrate hundreds of metres to the surface every night. Most have light organs along their flanks. They have fewer photophores arranged in patterns specific to each species. They are thought to aid species recognition in deep waters. Luminous patches near the tail may be used to dazzle or surprise a predator.

Not all of the deep-sea fishes are luminous. Generally species with large eyes have luminous organs while blind of small-eyed fish do not. Food is scarce in the deep sea, so the fishes are usually small. Predatory fishes inhabiting this zone often have very elastic stomachs which enable them to swallow prey several times bigger than themselves. In regions where there may be only one fish per cubic kilometre of water, the predators cannot afford to ignore any source of food.

One fish that lights its own way in this zone is the deep-sea dragon. It has rows of photophores arranged on its cheeks and running along the side of its body. Underneath its mouth is a very long, thin barbel which is very sensitive to touch. Using its photophores and its barbel, the deep sea dragon is well equipped to detect the presence of enemies as well as attracting prey.

[previous page]   [next page]