This fortnightly feature was published on August 29
The angler fish lure their prey

by Nutan Shukla

THE most well-known lure in the animal kingdom must be the one used by the angler fish. There are many species, some in coastal waters and others in the deep sea. Among these fish most familiar is the ‘monk-fish’ with its enormous, cavernous mouth. It spends most of its time sulking inconspicuously on the seabed, feathery outgrowths enabling it to blend in with its background. In place of passive lurking it uses active luring as soon as it spots a likely victim. On the front of its head the first dorsal spine stands alone and has a fleshy tip. As the prey swims near, the ‘fishing-rod’ is swung forward and jiggled furiously.

As a result the dancing lure is positioned just above and in front of the angler’s face. This patient predator waits and waits until, at the very last moment, when the prey fish is about to bite at the lure, the killer’s great jaws open and in a movement so fast that it can hardly be seen by the naked eyes, the fish swallows violently and the prey is drawn in with the inrush of water. Backpointing teeth of the fish prevent the prey from escaping. The ability to suck in water is so highly developed that it rarely needs to attack its prey with a forward lunge, like other fish. To prevent the lure being sucked in with the victim, the angler fish has the ability to swing its fishing-rod back, out of the way, as it opens its jaws, the whole procedure being performed in a fraction of a second. Atlantic anglers can grow up to 2 metres long and weigh up to 40 kg.

In the darkness of the oceanic abyss, the deep-sea angler fish attracts prey towards its ample mouth with an elongated first dorsal fin ray or illicium — the fishing line — which ends in a luminous, flashing, frilly ‘esca’ or bait. A branched appendage or barbel, which is faintly luminous, is slung under the lower jaw.

There are more than 200 species of angler fish known today and some of them are the strangest fish ever seen. In some of the deep sea species fishing line is such which can be retracted gradually when approached by prey fish, so that the victims are gently drawn closer and closer to the killer’s jaws, before the final, lethal gulp.

The ultimate deception is practised by one of the deepest of these deep-sea anglers. Instead of waving a luminous worm at the end of a filament, it lights up a special lure on the roof of its wide open mouth. The little victim swims happily into its gaping jaws to investigate this apparently tasty morsel and in doing so performs the final act of its life.

Among the deep sea species the luminous tip may take the form of a simple swelling or is embellished with frills and filaments to make an appetising-looking bait. These luminous lures are nothing but a patch of skin, without pigments, which allow the bioluminescence to shine through.

In the deeper parts of the sea, where light from the surface is barely visible or is absent altogether, light lures are common. This light is not produced by the fish but by symbiotic bacteria that are cultured in special compartments within the lure. They are encouraged to glow when oxygenated blood is pumped into the chamber. When at rest, the fish shuts down its light organ simply by temporarily cutting off the blood supply.

Some examples of these fish include the deep-sea, scaled dragon fish which have luminous chin barbels that are thought to attract prey to the mouth. One species sports a barbel 10 times the length of its body with a tip that is luminous.

The mid-water viper fish behave in a similar way to angler fish. They have a modified second dorsal fin spine, tipped with a luminous lure, that has become even more elongated.

The predator hangs motionless in the water, its head lower than its tail, with the fin-ray reaching over the head so that the lure dangles in front of the mouth. They look fearsome, with enormous mouths and gigantic teeth, but, fortunately, they are only 5 to 30cm long.