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Flatfish Facts and Pacific and California Halibut Information

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

A partially camouflaged California halibut

A partially camouflaged California halibut

More Than Just a Food Source

For many people, halibut are simply a good food source. I think they are interesting animals that are worth studying in their natural habitat. They are a type of flatfish. Flatfish have flattened bodies, as their name implies, and they swim on their sides. At the start of their lives, they look like other fish. During metamorphosis, they gradually change their orientation in the water so that they are moving with their right or left side facing the water surface and their other side facing the ocean floor. The eye on their lower side slowly shifts in position until it lies next to the one on their upper side.

Pacific halibut are the largest flatfish and can grow to be huge creatures. According to the California Department of Fish and Wildlife, the biggest animal on record measured nine feet in length and had an estimated weight of five hundred pounds. California halibut can also be big fish, but they don't grow as large as the Pacific type. The Monterey Bay Aquarium says that the California version reaches a maximum length of five feet and has a maximum weight of seventy-two pounds.

The fish hide by resting on the ocean bottom and covering themselves with sand or other sediments to camouflage their body. They are ambush predators and feed on fish and marine invertebrates. Both types are found on the Pacific coast of North America.

Platichthys flesus (the European flounder)

Platichthys flesus (the European flounder)

Pacific and California halibut belong to the order of fish known as the Pleuronectiformes. The Pacific halibut belongs to the family Pleuronectidae within the order Pleuronectiformes. The California halibut is classified in the family Paralichthyidae.

Flatfish Classification and External Features

Flatfish belong to the order Pleuronectiformes within the class Actinopterygii. The class contains the ray-finned fish. Flatfish are known for their flattened body with both eyes on one side and for the fact that the eyes protrude from the body. The fish primarily live on the ocean floor but also swim through the water. Around 800 species exist. The order has a very wide distribution and can be found from the Arctic to the Antarctic.

Though I focus on the Pacific and California halibut in this article, many other members of the order exist. Halibut, flounders, turbot, sole, plaice, sanddabs, and other fish belong to the order Pleuronectiformes. It’s an interesting group.

It's useful to look at the scientific name when studying a flatfish in order to avoid a potential identification problem. The common name "flounder" is used for some flatfish that aren't closely related, for example. Despite the mention of the word "halibut" in its common name, the Pacific halibut belongs to a family (the Pleuronectidae) that is often referred to as the right-eyed flounder family. The California halibut belongs to a family (the Paralichthyidae) that is also referred to as the large-toothed flounder family.

A line can be seen travelling along the middle of the fish in the photo above. The line is known as the lateral line because it can be seen on each side of a fish when the animal is in the usual orientation. It contains receptors that detect vibrations, currents, and changes in water pressure. Other fish and some amphibians also have a lateral line.

The elongated dorsal (back) and anal (lower) fins play a large role in the movement of a flatfish along the ocean floor. The animals swim through the water as well as over the ground. As they do this, they maintain their flattened posture. They are able to quickly disguise themselves in a sandy substrate, as shown in the video below.

Species of Halibut

There are two species of "true" halibut (those in the genus Hippoglossus)—the Atlantic halibut (Hippoglossus hippoglossus) and the Pacific halibut (Hippoglossus stenolepis). The Pacific halibut is found along the Pacific coast of the United States and Canada from California to Alaska. It's also found along the coasts of Russia, Japan, and Korea and in the Bering Sea. The California halibut has the scientific name Paralichthys californicus and is found from Washington to Baja California. It's also known as the California flounder.

The first part of the word "halibut" comes from the middle English word hali or haly, which means holy. The second part of the name is derived from the middle Dutch or German word butte, which means flatfish. The earliest appearance of "halibut" is found in fourteenth-century documents. Halibut were once considered to be a special fish and were eaten on holy days.

Top surface of a Pacific halibut (dark) and the bottom surface (white)

Top surface of a Pacific halibut (dark) and the bottom surface (white)

Identifying the Pacific and California Halibut

The upper surface of a Pacific and California halibut (with respect to its orientation on the ocean floor) has a mottled olive green, grey, brown, or black pattern. This helps the fish blend in with the sandy or muddy ocean floor. The lower surface is generally white. The white colour helps to camouflage the fish against the bright sky when they are swimming away from the ocean bottom and are viewed from below. Halibut do have scales, but they are small and smooth and are buried in the skin.

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Pacific Halibut

The body of a Pacific halibut has a triangular shape due to the protruding and pointed section of its long dorsal and anal fins. Most Pacific halibut swim with their right side uppermost, but a very small percentage—reportedly only 1 in 20,000 fish—have their eyes on their left side and swim with their left side uppermost. The fish are known for their large mouths.

California Halibut

A California halibut has an oval body. Unlike the case in the Pacific halibut, the dorsal and anal fins of the fish aren't triangular and are smoothly curved instead. California halibut have either their right or their left side uppermost. They have the ability to modify the colouration on their upper surface to blend in with the ocean bottom. They also have large mouths that contain many teeth. The teeth are sharp and can potentially give a human a nasty bite.

Diet and Predators

Even though they often spend time hiding in sediment on the ocean bottom, Pacific halibut are strong swimmers. They are carnivores that feed on other fish such as cod, pollock, turbot, rockfish, sculpins, and herring as well as on invertebrates such as shrimp, crabs, and octopuses. Most of their hunting occurs on the ocean floor, but they sometimes move into open ocean to catch their prey. The position of the mouth can make the fish look as though it's eating sideways as it grabs and munches its prey. The strange angle of the mouth in relation to the rest of the body can be seen in the video above.

California halibut are generally found in shallower water than Pacific halibut. Their main food is small fish, especially anchovies and sardines. They also eat squid. Like other halibut, they generally lunge at their prey from their hiding place but may chase the prey through open water if it escapes.

Halibut have several predators, including humans, killer whales, sea lions, and sharks. Pacific and California halibut are popular food fish for people. Their flesh is white in colour and has a flaky texture and a pleasant taste. Some meals of fish and chips use halibut as the fish. It's harder to find photos of wild flatfish on the Internet than of the ones that have been caught for food, which I think is a shame.

A California halibut from San Francisco Bay

A California halibut from San Francisco Bay

Reproduction of the Two Species

The Pacific halibut spawns in the winter, especially from December to February. The fish migrate from the shallower water of their feeding grounds to deeper water, where they release their eggs and sperm. A female produces from five hundred thousand to over four million eggs, depending on her body size. Many of these eggs are eaten by predators, but some survive and meet sperm. Females don't begin laying eggs until they are between eight and twelve years of age. Males become mature when they are around seven to eight years old.

California halibut mate between February and September and move into shallower water to breed. Fertilization is external. Females start releasing eggs at around four or five years of age, while males begin releasing sperm when they are two to three years old.

Life in Plankton and Metamorphosis in Flatfish

The fertilized eggs of halibut rise to the surface layer of the ocean and hatch into larvae after about fifteen days. (The times mentioned in this section depend on the species, water temperature, and probably other factors.) The larvae and young fish are free-floating for as long as six months and are carried long distances by ocean currents. They feed on animals in the surrounding plankton. Plankton is a collection of tiny and microscopic plants and animals in the ocean. The organisms in the plankton can't move on their own or are very weak swimmers.

A very young flatfish at first looks like other fish. At some point, the body begins to flatten and one eye starts its migration to the other side of the fish. Pigment appears on the upper side of the animal's body and other changes occur. The animal finally settles on the ocean bottom, lying on its side with its pigmented surface upwards. The change in the animal's appearance is known as metamorphosis. The time when it begins varies. In fish farms, the change in the Atlantic halibut starts when the young fish is about seven weeks old.

Some biologists are studying the fascinating process of metamorphosis in order to understand it better. They know that thyroid hormones play a major role in the process. The changes in metamorphosis include more that just the obvious external ones. Internal changes occur in the fish as well.

The longest known lifespan for a Pacific halibut is fifty-five years. California halibut have lived for as long as thirty years.

Pacific Halibut Migration

Tag and release programs have shown that some Pacific halibut—especially young ones—participate in long distance migrations as well as seasonal ones. The initial sites where the young halibut settle are referred to as nursery grounds. After living there for two or three years, the youngsters migrate to a permanent home. This journey may take several years. Older halibut may migrate, too. The longest recorded migration of a Pacific halibut took the fish from the Aleutian Islands to Oregon, a journey of 2,500 miles.

Food and Nutrition for Humans

Halibut are an important food resource for humans. They're caught in commercial, subsistence, and recreational fisheries. The fish are rich in protein and are a great source of B vitamins and certain minerals. They are also low in saturated fat and contain omega-3 fatty acids, which are believed to have important health benefits.

Omega-3 fatty acids may improve the health of our cardiovascular system, improve brain function, and reduce inflammation. They may also play a role in reducing the risk of some types of cancer. Although halibut contain these potentially beneficial fatty acids, they also contain a moderate amount of mercury, so their consumption should be limited. Salmon and sardines are a lower-mercury source of omega-3 fatty acids.

A California halibut can be seen at the 5:55 mark in the following video about marine life around the Californian Channel Islands. The islands form a chain off the coast of Southern California.

Discovering More About the Animals

In addition to being a nutritious food, halibut are interesting creatures and potentially long-lived animals. Their development is very unusual. There's still a lot to be learned about their behaviour.

I think it's a great shame that the fish are often appreciated for their food value but not for their natural history. The vast majority of the YouTube videos about the two fish that I've seen describe how to catch them and how to prepare them for a meal instead of showing their life in the ocean.

Hopefully, the populations of both the Pacific halibut and the California one will continue to be monitored and carefully managed throughout their range. I think it's important that some of these fish live their full lifespan and help us to learn more about the fascinating world of marine life.


  • Flatfish movement on the ocean floor from Northern Arizona University
  • Thoughts about flatfish and their evolution from PBS Nova
  • "Pacific Halibut (Hippoglossus stenolepis)" from the Alaska Department of Fish and Game
  • Information about the Pacific halibut from the California Department of Fish and Wildlife
  • California halibut fact sheet from the California Department of Fish and Wildlife
  • More California halibut formation from the Monterey Bay Aquarium
  • Eating the fish (halibut of different species): pros and cons from WebMD (This article was reviewed by a dietitian and is a good nutritional reference, which is why I have included it in this section. Saying that eating halibut reduces the risk of certain diseases is fine if the evidence supports this, but the writer of the article sometimes makes the claim that eating the fish prevents a health problem, which no writer can guarantee.)
  • Potential health benefits of omega-3 fatty acids from Colorado State University Extension

© 2012 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on July 03, 2014:

Hi, Peg. Yes, the fish is huge! The halibut is an interesting animal. Thanks for the visit!

Linda Crampton (author) from British Columbia, Canada on July 03, 2014:

Hi, Rebecca. I think that ocean creatures are awesome, too! Thank you very much for the visit and the comment.

Peg Cole from North Dallas, Texas on July 03, 2014:

That fish in the first picture is huge. Wow. It's kinda creepy, too. I never knew that they started out with eyes on both sides and that one moved over. Eeek.

Rebecca Mealey from Northeastern Georgia, USA on July 03, 2014:

The ocean holds so many awesome creatures! Thanks so much for sharing this. Well researched!

Linda Crampton (author) from British Columbia, Canada on July 03, 2014:

Thank you very much for the comment, the vote and the share, ologsinquito!

ologsinquito from USA on July 03, 2014:

This is a very interesting article about a very interesting fish. Voted up and shared.

Linda Crampton (author) from British Columbia, Canada on November 08, 2012:

Thank you very much, aviannovice! I appreciate your visit and the great comment.

Deb Hirt from Stillwater, OK on November 08, 2012:

An excellent piece! I enjoyed the video, as well as all the info that you provided. I was not aware that the eyes migrated during growth. Again, great job!

Linda Crampton (author) from British Columbia, Canada on July 20, 2012:

Thank you for the comment, teaches. The life cycle of the Pacific halibut is interesting. I'm hoping that researchers learn more about the behavior of the fish soon.

Dianna Mendez on July 20, 2012:

I now know what this fish looks like and more about its life habits. Another interesting post and well done.

Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Hi, Prasetio. Thank you very much for the comments and all the votes. I appreciate them!

prasetio30 from malang-indonesia on July 19, 2012:

Very informative hub, Alicia. I had never heard about this fish. Thanks to introduce Halibut with us. I wish I can see it in person. Voted up and press the buttons, except funny. Take care :-)


Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Thank you very much for the comment and the vote, susiebrown48. It's nice to meet you!

susiebrown48 from Clearwater, FL on July 19, 2012:

Fascinating! We fish but I've never encountered a Halibut. Loved your well-written, insightful, well researched article. Voting up!

Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Thank you for the visit and for the witty and amusing poem that brightened up my day, drbj!

drbj and sherry from south Florida on July 19, 2012:

Hi, Alicia, What a strange fish is the halibut.

It starts life as round then becomes flat just for the hellavit.

It's bigger than flounder. Flatter, not rounder,

With a migrating eye, near as I can tell of it.

Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Thank you for the comment, Peggy. Thank you for all the shares, too! I appreciate them very much. It is amazing that halibut can become so big.

Peggy Woods from Houston, Texas on July 19, 2012:

We love eating halibut and knew that it was a flatfish. Had no idea that they can live to be so old or that they can be so large. I watched every video and found them fascinating. They truly blend into the ocean floor perfectly with their coloration on the one side. Voted this up, useful, interesting + tweeted and sharing with my followers. Thanks Alicia for another fascinating hub!

Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Thank you very much for the comment and for the interesting information as well, Augustine.

Linda Crampton (author) from British Columbia, Canada on July 19, 2012:

Thanks, Lesley. Halibut and the other flatfish are very interesting fish. I enjoy learning about their lives!

Augustine A Zavala from Texas on July 19, 2012:

Northwest coast indians used to make Halibut lures made out of carved wood shaped like little men. The leader was made of a weaker rope than the mainline, so if they hooked a giant fish it could break free. Completely interesting!

Movie Master from United Kingdom on July 19, 2012:

Hi Alicia, I had no idea the Halibut could live up to 55 years and their eyes can be on the same side! fascinating information and educational hub.

Halibut is one of my favourite fish, it's delicious!

Many thanks and voted up

Linda Crampton (author) from British Columbia, Canada on July 18, 2012:

Hi, alocsin. Yes, halibut can get very big! It's amazing how heavy they can get, too. Thanks for the votes.

Linda Crampton (author) from British Columbia, Canada on July 18, 2012:

Thanks for the comment and the votes, b. Malin! Halibut is certainly a very versatile food, and it's good to know that it's nutritious and healthy, too - apart from its mercury content.

Aurelio Locsin from Orange County, CA on July 18, 2012:

Talk about a big fish in a big pound. Thanks for introducing me to creature, though now I'll think twice about eating it. Voting this Up and Interesting.

b. Malin on July 18, 2012:

So Educational Alicia. I like Halibut, can be cooked in many delicious ways. Don't have it too often because of Mercury...Actually like Salmon better. I found this Hub so Interesting and Informative, loved looking at the Videos as well. Voted it UP and Interesting and Useful!

Linda Crampton (author) from British Columbia, Canada on July 18, 2012:

Thank you very much, GoodLady. I appreciate the comment and the pin. I'm looking forward to meeting you on Facebook!

Linda Crampton (author) from British Columbia, Canada on July 18, 2012:

Thank you for the comment and the votes, Tom. I appreciate your visits to my hubs and your kind comments very much!!

Penelope Hart from Rome, Italy on July 18, 2012:

Superb material in your Hub and I enjoyed reading it very much, enjoyed learning so much (including its nutritional value and that it is such a carnivore! Will pin this. (I don't get on with Facebook yet, but might try Facebook too). Voting etc.

Thomas Silvia from Massachusetts on July 18, 2012:

Hi my friend, this is all interesting information and facts on the Halibut, an most of it i did not know before,thanks for helping me learn more about this fish.

Vote up and more !!!

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