Marine Creature of the Month JULY

Angler Fish

Photo from Creatures of the World Wikia

Kingdom: Animalia

Class: Actinopterygii

Conservation Status: Vulnerable (VU)

Found: Worldwide

Diet: Carnivorous

Weight: Up to 45kg (100lbs)

Size: 20cm (8") to 1m (3')

Habitat: Some species are pelagic, some are benthic.

Everyone knows of the iconic angler fish. Big, gaping mouth full of spiky teeth and a dangling blob of light hovering just in front of its face, illuminating all that terror. There is more to this fish, seemingly made of nightmares. Did you know that there are two types of angler fish species? The image which comes to mind is that of the ones which live deep under the sea, near the sea bed. These are the benthic species, which are compressed dorsoventrally (face to tail) making them short and squat with an upturned mouth. But there are also palegic species, which live much closer to the surface. These are compressed laterally (at the sides) making them long and thin. Both types occur across the globe and boast a variety of species.

Angler fish are a bony fish from the teleost order Lophiiformes. The word "teleost" is derived from Greek and means "complete bone". These bony fish have been in our waters since the early Cretaceous era, roughly 100-130 million years ago. Some context, these fish were swimming about while the Tyrannosaurus Rex dominated the land above. That immediately makes these guys awesome in my book.

Everything about the angler fish is designed to help it hunt, both benthic and pelagic species. They have both adapted ways to make them effective hunters. Pelagic angler fish are ambush predators. They are camouflaged to blend in with seaweeds and rock, and they use their illcium (the dangly bit) to lure prey by wiggling it in all directions before devouring them whole. Unlike their benthic cousins, their illcium does not glow. It doesn't need to, as they are living in a much lighter environment and do not need to utilise bioluminesence as a lure. The benthic species do glow, as 200 fathoms below the surface there is no light. They, too, are camouflaged but to dark grey colours and their angled mouth is perfect for grabbing prey. The angler fish can distend its jaw and stomach, thanks to their thin and flexible bones, to capture prey much larger than itself. Their teeth help to trap them too.

So why do the benthic angler fish glow? They have a simbiotic relationship with bacteria which reside in a gland called the esca. This is the end of the illcium, the bit which glows. While used to lure in prey, it is also theorised that they are used as a mating call. The illcium is a modified dorsal ray and the esca is open to the sea water. It is believed this is how the bacteria enters the esca, but tests have been conducted on the waters and no trace of the bacteria have been found. It is also postulated that the angler fish actually secrete the bacteria themselves. It is somewhat of a mystery.

All the angler fish who possess these traits I have spoken of so far are female. Literally all of them. Angler fish have a massive difference between the males and females of the species. The females are much larger than the males, to the point where the males are entirely dependant on the females. The males are much too small to effectively hunt and they won't fully develop until they attach themselves to a female. Literally, attach. They will bite a female and release an enzyme which will digest both the male's face and the female's skin until they can fuse down to the blood vessels. Whatever the female eats feeds the male too.

This is also how they mate. The male is just there to provide everything the female needs to spawn. This is called parabiotic reproduction. In addition to this, a female can have anything up to eight males attached to her, which makes them polyandrous maters. (Meaning more than one "partner".) Imagine eight boyfriends living directly off your body! These angler ladies put up with a lot. This is possibly due to the low density of females in their population. Whatever the case, they deserve a medal.

Photo from We Hunted the Mammoth

Fun facts:

• Some species of bacteria found in angler fish esca cannot bioluminese without the angler fish.
• Angler fish can eat prey up to twice their size!
• Some males have well developed olfactory glands and eyesight from birth, so that they might find their sexy angler lady quickly.
• Males are completely dependant on the females.
• Angler fish are considered to be one of the ugliest fish, which is unfair. They are amazingly adapted to suit their environment and hunting style. Beauty is irrelevant.

Check out the #MCotM July board!