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Facts About Cusk Eels and Some Interesting Species

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

The Cusk Eel Family

Cusk eels are an interesting group of fish. Though they have elongated bodies and long fins, they aren't eels, despite their name. Some species have unusual characteristics. The faceless cusk often appears to have no face, as its name implies. At least some species of cusk eels produce sounds during courtship. Some have functional eyes while others don't. Many species live in deep water and lead mysterious lives.

In cusk eels, the pelvic fins seen under the body of many fish have moved forward and become long and slender barbels under the head. True eels don't have pelvic fins. Cusk eels belong to the order Ophidiiformes and the family Ophidiidae. True eels belong to the order Anguilliformes.

Like the word "eel" in the cusk eel's name, the word "cusk" is used for another type of fish. A cusk eel is not closely related to the fish known as a cusk. The latter animal (Brosme brosme) belongs to the ling family, or the family Lotidae. It's caught for food. It has an elongated body and long fins, but it has multiple features that are different from those of a cusk eel.

The snake blenny has features of a typical cusk eel, including barbels.

The snake blenny has features of a typical cusk eel, including barbels.

External Features of a Snake Blenny

Cusk eel bodies range from large and bulky to comparatively small and dainty. Despite these differences, the bodies of the different species have some similar features. The snake blenny (Ophidion barbatum) belongs to the cusk eel family. The fish has the elongated body, long fins, and sensory barbels of a typical cusk eel. The fish is a good animal for observing the basic features of its family. The scientific name should be examined when a fish is identified as a "snake blenny" because the name is used for some animals outside the family Ophidiidae.

The cusk eel version of the snake blenny is found off the coast of southern England and Europe and in the Mediterranean Sea. It's referred to as a demersal fish because it lives close to the ocean bottom, as most cusk eels do. Its barbels are sensitive to taste and perhaps other sensations and help it to find food on the ocean floor. Cusk eels feed on invertebrates and sometimes on smaller fish as well. The snake blenny is eaten by bottlenose dolphins and other predators. Its maximum length is said to be around 25 cm or 9.8 inches.

The female snake blenny lays eggs. Fertilization in the species is external. The male releases his sperm on top of the eggs. The fertilized eggs are sometimes seen floating on the water surface in gelatinous masses.

The fins of a cusk eel are related to those of a typical bony fish (such as this Lampanyctodes hectoris or Hector's lanternfish) but are modified.

The fins of a cusk eel are related to those of a typical bony fish (such as this Lampanyctodes hectoris or Hector's lanternfish) but are modified.

In the illustration shown above, the numbers represent the following fins.

1: pectoral fins (paired)

2: pelvic fins (paired)

3: dorsal fin (single)

4: adipose fin (single)

5: anal fin (single)

6: caudal fin (single)

Fins of a Cusk Eel

As in other members of its order, the fins of the snake blenny are modified from the typical pattern that is seen in bony fish and shown in the illustration above.

  • The dorsal, tail, and anal fins are joined to form one continuous structure of roughly the same size and shape throughout. (The adipose fin shown in the animal above isn't present in all fish species.)
  • The fin is pointed at the tail end. In some species, it's slightly differentiated in this region. It isn't forked, however.
  • The pelvic or ventral fins have moved forward to near the front of the head and have become slender barbels.
  • The pectoral fins are in their original location.

The Faceless Cusk

Like the snake blenny, the faceless cusk (Typhlonus nasus) belongs to the family Ophidiidae. The animal often seems to have no face, as its name suggests. Its head is large and bulbous. The fish has small eyes, but they are covered with skin and may not be visible. The mouth is located on the underside of the head instead of at the front, which contributes to the faceless effect. The nostrils are visible and are arranged in two pairs, one on each side of the head.

I've seen photos of faceless cusks with and without eyes. The Fishes of Australia website says that there is no external evidence of eyes "at least in large individuals." The scientists investigating the fish agree. This suggests that the eyes become less visible as the animal grows. There may be other factors at play with respect to the presence or absence of eyes, however. We still have a lot to learn about the species. Faceless cusks without visible eyes can be seen in the "Species Image Gallery" in the Fishes of Australia reference at the end of this article as well as in the Marine Biodiversity Hub article.

The faceless tusk is found off the coast of Australia. A living animal was filmed in 2016 (the one shown in the photograph above). A specimen was caught in 2017. Before that time, the last representative of the species captured in the area was an animal dredged up in 1873. The fish lives in deep water, where it's difficult to observe. As one scientist exploring the animal has said, based on the illustration below the modern fish looks heartier than it did in the past.

An 1887 illustration of a Typhlonus nasus specimen discovered during the H.M.S. Challenger expedition in 1873 to 1876

An 1887 illustration of a Typhlonus nasus specimen discovered during the H.M.S. Challenger expedition in 1873 to 1876

Sound Production in Cusk Eels

It's known that some fish produce sounds by vibrating their swim bladder. These sounds have been recorded. A swim bladder is a sac that is filled with a variable quantity of gas. It enables a fish to adjust its buoyancy in the water. In some fish, it has an additional function. Vibrating the swim bladder rapidly can produce sounds.

The striped cusk eel referred to in the video above has the scientific name Ophidion marginatum. It lives in the northwestern section of the Atlantic Ocean and produces sounds during courtship. Fish sounds are usually produced by the male in order to attract a female during the mating season. Some researchers have found that the females of two deep-water cusk eel species (Genypterus chilensis and Genypterus maculatus) also produce sound, however.

Sounds created by some cusk eel species have been heard, as shown in the video. In other species, the anatomy of the swim bladder area leads researchers to suspect that the animals produce sounds, based on their prior knowledge of sound-production in fish. The details about how the group produce sound are still being studied.

In some fish, the sonic muscles are attached to the swim bladder and are the direct cause of its vibrations. In others, the sonic muscles are attached to another structure, such as a bone. This structure then causes the vibration of the swim bladder once the sonic muscles become active. The cusk eels that have been studied use the second method to create sounds.

A Close Relative of the Family Ophidiidae

The animals in one group of fish in the order Ophidiiformes but not in the family Ophidiidae are sometimes referred to as a type of cusk eel. Until recently, these animals were said to belong to the family Aphyonidae, or the blind cusk eel family. Some sources still use this family name. Others use the new placement of the fish in the family Bythitidae, which is sometimes known as the live-bearing cusk family.

The word "aphyonids" is used as the general name for the fish in the group, despite the official change in their family name. Aphyonids are interesting because they live in deep water and were never seen alive until the video below was made in 2016. Dead animals in the family had been discovered in dredged material, but not living ones. Several genera have been discovered in the group since the video was made.

The fin arrangement in aphyonids is mostly the same as that in the Ophidiidae family. The pelvic fin is modified in a different way, however. It consists of a single spine or is missing altogether.

Aphyonids have almost transparent skin that is gelatinous in nature and has no scales. Their eyes are rudimentary and are said to be nonfunctional. As the species in the video below shows, the fish can have a ghostly appearance. They have no swim bladder. They are viviparous, which means that they give birth to live young. The female is capable of storing sperm until it's needed.

An Intriguing Group of Fish

Cusk eels and their close relatives have some intriguing features. Many species in the group are still mysterious in multiple ways. In tropical and subtropical areas, cusk eels are believed to be the dominant fish living on the ocean floor. It's interesting to speculate about the presence of unknown species in deep and hidden habitats.

As our ability to explore the deep ocean improves, we may make some more discoveries about the family Ophidiidae. The scientist in the "Sounds of the Striped Cusk Eel" video above says that researchers haven't always realized that underwater fish sounds that they hear are coming from a cusk eel. There's still a lot to learn about the animals. I'm looking forward to future reports about their features and behavior.

References

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on November 10, 2020:

Thank you very much for the kind comment, Ann. I think that biology and nature are fascinating topics.

Ann Carr from SW England on November 10, 2020:

It never ceases to amaze me how much knowledge and research you have with these hubs on wildlife. These eels are fascinating, among many of those we don't tend to hear about - thanks to you, we do here!

Ann

Linda Crampton (author) from British Columbia, Canada on November 10, 2020:

Thanks for commenting, Eman. I think that marine life is very interesting.

Linda Crampton (author) from British Columbia, Canada on November 10, 2020:

Thanks, Devika. Cusk eels and their relatives are interesting to explore.

Linda Crampton (author) from British Columbia, Canada on November 10, 2020:

Thank you for the visit, Dora. The faceless tusk is certainly a strange animal.

Eman Abdallah Kamel from Egypt on November 10, 2020:

An interesting article to read. Thank you, Linda, for sharing all this useful information about Cusk eels.

Devika Primić from Dubrovnik, Croatia on November 10, 2020:

Linda this is curious and fascinating about Cusk eels. The facts are interesting and unique. Your research is in detail. I enjoy learning about deep water creatures.

Dora Weithers from The Caribbean on November 10, 2020:

There are so many fascinating facts about this somewhat faceless creature. I don't know that I would have called it a fish. Thanks for the continuing education you provide on these mysterious creations.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

An "alien world" is a great description, Heidi! Exploring the area in person would be very interesting.

Heidi Thorne from Chicago Area on November 09, 2020:

These deep water discoveries are truly fascinating! The documentaries I've seen on these areas show an almost alien world of creatures we can't even imagine. Thanks for introducing us to another creature!

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

I agree, Mary. There are so many interesting life forms on Earth that we don't learn about in school. Nature is never boring!

Mary Norton from Ontario, Canada on November 09, 2020:

It is interesting to know something about some of these species that we are not familiar with and never see. We haven't learned much about them in school.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

I hope that's the case, Denise. I think undersea life is very interesting. Blessings to you, too.

Denise McGill from Fresno CA on November 09, 2020:

I guess as we are able to go deeper we will find many more mysterious fish and life there.

Blessings,

Denise

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Linda. Some unusual cusk eels exist. The faceless cusk is impressive!

Linda Chechar from Arizona on November 09, 2020:

Those cusk eels! I didn't know they were so weird that are species below the bottom of the ocean floor. The cusk eels have hidden habitats that crazy looking faces!

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

I appreciate your kind comment. Peggy. I hope you have a great week.

Peggy Woods from Houston, Texas on November 09, 2020:

Your articles are always a joy to read. I learn so much new information about the creatures that live on earth, or in this case, the depths of the oceans. All of the videos were well worth watching. Thanks!

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Thanks, Maren. Earth has some very interesting organisms.

Maren Elizabeth Morgan from Pennsylvania on November 09, 2020:

Another fascinating exploration of our fellow earth travelers! Thank you, Linda.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Bill. It's certainly amazing what lives on the ocean floor. It's a very interesting place! I appreciate your comment.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Ankita. Yes, nature is always interesting. I enjoy exploring the world of living things.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Flourish. Yes, the faceless cusk is very interesting. It's a strange animal. I would love to know more about the changes in its eyes.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Thank you very much, Bill! I hope you have a great week, too.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Nithya. I hope researchers discover more about the animals soon. There seems to be a lot to learn about them. Thanks for the visit.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Liza. Yes, the first photo is interesting! I would like to know more about that particular cusk eel. Thanks for the visit.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Thank you very much for the visit and the comment, Pamela.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, Eric. The nature of the deep ocean floor is intriguing. I hope scientists learn more about the region soon. As always, I appreciate your comment.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Thank you very much for the comment, Fran.

Linda Crampton (author) from British Columbia, Canada on November 09, 2020:

Hi, John. Thanks for the comment. I think the world of nature is fascinating.

Ankita B on November 09, 2020:

Interesting article about Cusk Eels. There are so many fascinating marine organisms with whom we are not even familiar. Its always great to learn about them.

FlourishAnyway from USA on November 09, 2020:

What a strange animal with no face! Thanks for presenting this information. I was intrigued regarding the faceless cusk having gone MIA for so many years then making a reappearance.

Bill Holland from Olympia, WA on November 09, 2020:

As always, wonderful information. Thank you! I'm a big fan of these articles of yours, Linda! Keep them coming, please, and have a brilliant week ahead!

Nithya Venkat from Dubai on November 09, 2020:

An interesting and informative article about the cusk eel. Thank you for sharing, they are certainly intriguing and I hope researchers come out with more information about the cusk eels.

Liza from USA on November 09, 2020:

I like the first photo a lot, the grumpy-looking cusk eel. It blows my mind that they have found the fish at a depth of 1,585 meters or 5,200 feet. Thank you for sharing an informative article, Linda. Every time I read your article, I learn something new.

Pamela Oglesby from Sunny Florida on November 09, 2020:

The Cusk Eel is an unusual species and it really doesn't have a face. I think it is also unusual that it can adjust its buoyancy. I like the pictures and videos. This is a very well-written, interesting article, Linda.

Eric Dierker from Spring Valley, CA. U.S.A. on November 09, 2020:

Really interesting and as expected well done. I have a hard time even imagining the depths. I will never look at an eel the same.

fran rooks from Toledo, Ohio on November 09, 2020:

Linda, I always learn so much from your articles. They are so informative. Thanks again for another great article.

Bill De Giulio from Massachusetts on November 09, 2020:

Another fascinating article about a species I was not familiar with. The cusk eel does have a rather grumpy looking face. It’s amazing what lurks on the ocean floor. Thank you again for the education.

John Hansen from Queensland Australia on November 09, 2020:

You always find interesting and little known creatures to write articles about, Linda. I now know a lot more than I did previously about the cusk eel. Thank you.

Linda Crampton (author) from British Columbia, Canada on November 08, 2020:

Thank you for the kind comment, Liz.

Liz Westwood from UK on November 08, 2020:

This is an extremely well-presented and well-illustrated article. You use different medis, such as video, very well, to illustrate this interesting article.

Linda Crampton (author) from British Columbia, Canada on November 08, 2020:

Thank you very much, Chitrangada. I appreciate your visit and comment.

Chitrangada Sharan from New Delhi, India on November 08, 2020:

Great informative article about the Cusk Eels. Nature is full of such interesting and amazing creatures, about whom we know so little. Your articles are always educative and well researched.

Thanks for sharing.