Nutrition
The female anglerfish is equipped with a modified
first-dorsal fin spine placed on the tip of the snout called an
illicium. The illicium has a single distal appendage, called an
escal that has a filamentous quality that allows it to move
swiftly while being pulled through the water. The escal
varies between anglerfish species but it often represents
invertebrates such as worms and crustaceans. In a nonluring
situation, the illicium is laid back over the head with the
escal tucked next to the dorsal fin. While luring, the illicium
is extended straight forward in front of the mouth (Pietsch,
1978).
Luring is achieved by a combination of bioluminescence and escal
movements that simulates the motion of worms and crustaceans.
The escal and distal appendages are wriggled, vibrated, swung,
and swept in order to attract the angler’s choice of prey.
Female ceratioids are gape-and-suck feeders. The combination of
the expansion of the mouth, creating a large increase in volume,
and the rate at which it is expands results in suction pressure
inside the mouth. Compared to other teleosts, the female
anglerfish have a more flexible and much larger oral cavity that
provides a more effective sucking function. The gape-and-suck
feeding is adapted to pull large prey inside the mouth past the
teeth. The prey is then transported through the pharynx, forced
through the esophagus, and finds its fate in the stomach (Pietsch).
Living at great oceanic depths, it seems anglerfish cannot
afford to let a meal go by, no matter how large or small.
Anglerfish consume a wide variety of food sources including
zooplankton, fish, crustaceans, cephalopods, and sea urchins.
Occasionally, there have been reports of female anglerfish found
floating with large fish caught in the mouth and throat. The
teeth of the anglerfish are folded inward, which provides no
mechanism for the removal of large prey once engulfed (Pietsch).
In the deep sea where very few organisms are present, consuming
sizeable energy-rich food sources is a successful strategy.
Anglerfish seldom feed and practice a very inactive lifestyle.
The structural and behavioral adaptations involved in the
energy-saving luring method played an important role in the
evolutionary success of the anglerfish (Pietsch, 1978).
At an early stage, the male anglerfish depends on the female
anglerfish for survival. When a male anglerfish finds a female,
he attaches to her skin by releasing an enzyme that digests the
skin and fuses the pair down to the blood-vessel level. The
female provides protection and nutrients to the male through their shared
circulatory system. In return, the male provides sperm to the
female anglerfish when she is ready to
spawn. The female and
male anglerfish have a symbiotic relationship (Munk, 2000).
A variety of ceratioids species have been found in the stomachs
of black scabbard fish, longnose lancetfish, and sperm whales.
The bones of a large ceratioid anglerfish was also reportedly
found in the stomach of a Deep-sea Swallower Saccopharaynx
lavenbergi. The primary diet of the Saccopharynx is unknown but
they are thought to feed on large fishes (Pietsch).