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We’ve mentioned the group of fish known as "anglers" a few times before in this series. Members of this group are ambush predators that use a lure on top of the head to draw prey towards the mouth. This lure is actually an extension of the dorsal fin rays. It consists of a long, thin strand called an illicium which is tipped with an esca, or bait.

The monkfish (Lophius americanus) is a member of a sub-group of anglerfish known as Lophiids. Although all anglers are strictly carnivorous, the lophiids are especially aggressive. The body and head is more flattened compared to other other anglers like sargassumfish.

Monkfish actually have three illicium used to attract food, again all of them being modified extensions of the first dorsal fin. The longest arises from the head just behind the top lip and serves as the primary lure. The illicium is very flexible and can be swiveled in any direction. The fish can also move just the very tip of the structure to trick other fish into thinking its a worm wriggling through the water. The second illicium sits right between the eyes and the third near the back of the head.

Not only do the illicia attract prey, they also serve as a trigger mechanism to induce feeding. In a reflexive response to anything touching any of the three structures, the fish will raise its head and snap its huge mouth open, drawing in any unfortunate fish that happens to have brushed against it.

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This fishing method wouldn’t work very well if the predator was easily seen. Camouflage is key to this working, and as you can see above, this fish has got this skill well covered. Not only do the odd growths all over the head help it to blend in with with weeds, they also serve to break up the fish’s natural shape so that it can camouflage on nearly any type of surface. It can even change the color of the skin, from black on mud, light brown on sand or, as you can see in this photo, green on algae. Although the young are much better at this than the adults.

Monkfish look like they are made up of all head and little body. The mouth is enormous and is capable of engulfing prey even larger than the predator itself. Many fish, such as groupers, also have unusually large mouths, but for groupers they need to be careful about what they try to swallow. I’ve seen some of mine try to eat fish that can fit into the mouth but has no way of actually reaching the stomach. These fish will swim around for hours with just the prey’s tail sticking out and eventually have to spit it back out or choke to death. Monkfish don’t have this problem.

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This is a monkfish skeleton I have hanging from the ceiling of my education center. As you can see, the ribs are spread unusually wide. Anything the monkfish can fit into its mouth simply slides right past the rib cage and into the stomach. And since the scaleless skin is as flexible as a rubber band, the stomach and skin simply stretches to accommodate whatever huge meal the mouth sends its way.

In fact, the skin is so flexible, and the wide ribs so delicate, that a beached monkfish is unable to support its own weight and collapses into a nearly shapeless blob. Which reminds me of the first monkfish I ever saw, when I was just a kid. Walking along the beach I came upon a very large, hideous looking animal stranded on the shore. It was a slightly decomposed monkfish, and while trying to figure out why it died I kicked it over onto its back with my foot. Sticking out of the belly was a seagull’s head. Apparently the bird was still alive in the stomach and did a bit of internal damage before expiring.

This is where this animal gets its other common name, "goosefish". While normally a deep-water fish, they will move closer to shore during the winter. And although their main prey are other fish, visiting shallow water gives it access to another type of food: Birds. Seagulls, cormorants, sea ducks and other waterfowl are all known to have fallen prey to the goosefish.

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Being able to capture large prey and having a stomach that can accommodate this food is great. But it won’t do the fish any good if it can’t keep the prey from escaping once it's caught, and then somehow move the mass of flesh down the throat. This is where the teeth comes in. Both jaws are lined with rows of long, sharp teeth that curve inward. Fish with needle-like teeth don’t chew, they swallow their food whole. The teeth are simply used to keep the prey from escaping. In addition to the mouth teeth, monkfish also have hundreds of smaller pharyngeal teeth lining the roof of the mouth and the throat. Again these point inwards, and by flexing the muscles in the throat the fish can use these teeth to slowly ratchet the prey down towards the stomach.

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Let’s look at that top drawing again. If you remember from Fins 101, the pectoral fins of a fish are the paired structures behind the gills, analogous to a bird’s wings. Most fish use these for steering and turning. Monkfish are what we call pediculate fishes, in that the pectorals are shaped like little arms, and even seem to bend at the elbows. And, yes, the fish can actually "walk" across the bottom with these. Fish have carpal bones in their fins (ie: fingers), but in most species these bones are too small to be seen externally. The carpal bones of the monkfish are greatly elongated, with fin webbing in between the fingers. This is what gives the fin that unusual bend to it. While the pectorals of most fish are behind the gills, anglers are the only group of fish whose gills actually sit behind the pectorals.

The paired pelvic fins, normally found on a fish’s chest, are also unusual in this species in that they are found just under the chin and form a pair of little kickstands for the head to rest on. This puts the mouth in a more upright position and helps make hunting more efficient. See how much more vertical a hunting angler looks when propped up on these fins.

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By the way, this is also a threatening posture, so if you see one in this position don’t put your hand anywhere near the mouth.

Like all anglerfish, female monkfish create a structure called an egg veil, a  thin band of floating gelatin that may be up to seven feet long and is embedded with hundreds of thousands of tiny eggs. This veil floats at the surface for about a month and then sinks to the bottom when the eggs hatch. The number of veils present can help predict how healthy the benthic population of monkfish are in any given area. NOAA even has an egg veil sighting program where fishermen and volunteers catalog floating veils and report their findings. This is part of an effort to try to better understand and manage this species, which has not done well at all under modern fishing pressures.

Once the eggs hatch the larvae are planktonic for a short time, metamorphosing into stranger and stranger looking creatures. The final surface stage, before sinking to the bottom, looks like something out of an Alien movie. I’ve only seen one in my life, about an inch long, and this drawing doesn’t do its freakishness justice.

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(Image via Bigelow and Schroeder.)

Monkfish are edible, and many of you may have even tried this. It is normally sold only as fillets since nobody would buy it from a market with a face like that. This fish should not be eaten, however, since it is listed by Seafood Watch as an unsustainable fishery. Most of the damage to the populations are not because of the demand for the flesh, but for the rich liver that is highly sought after by Japanese chefs, where it is used in sushi restaurants and goes by the name Ankimo.

Fun Fact: Aristotle was the first person to describe the "lure feeding" method of anglerfish way back in the 3rd century BCE.

Other diaries in this series can be found here.

Originally posted to Mark H on Thu Nov 15, 2007 at 07:41 PM PST.

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