ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Fish: The Characteristics of Jawless Fish, Cartilaginous Fish, and Bony Fish

Updated on September 7, 2014
Spiny Seahorse
Spiny Seahorse | Source

What are the characteristics of fish?

Fish are vertebrate animals (animals with a backbone) that have gills and live in the water (although some fish are amphibious and can come onto land for periods of time). Fish come in many different shapes and sizes. And not all of them look like fish!

To the right is a photo of a spiny seahorse. Is it a fish? It certainly lives in water. It has a backbone. And yes, it has gills. Seahorses are fish! Like most fish, seahorses have a swim bladder which helps them move up or down in the water. Seahorses are not very good swimmers though. For that reason, they often stay in one place for days, holding onto something by wrapping the end of their tail around it. While many seahorses are camouflaged in their environment, others can change their color to further blend in.

Would you like to hear about some other fish, and learn more about the common characteristics of fish?

Do you say "Fish" or "Fishes" to mean more than one fish? What's correct?

(You'll find the answer farther down this page, but first, see if you can answer it!)

I think the plural of fish is ....

See results

Characteristics of fish

  • Gills - Water goes into the fish's mouth and then over their gills (which are made up of rows of gill filaments) before leaving the fish out of the gill slits. There are many blood vessels in the gills. Oxygen from the water moves into these blood vessels. Once the oxygen is in the blood, it is carried throughout the fish's body, supplying the fish's cells with oxygen.

    Fish gills have countercurrent flow, which means that water passes over the gills in one direction, while blood moves through the capillaries in the opposite direction. Countercurrent flow increases the efficiency of respiration.

  • Single loop blood circulation (except for lungfishes) - This means that the blood flows through the heart to the gills, to rest of the body's tissues, and back to the heart in a single loop. Fish have two pumps, but four parts to their heart: the sinus venosus ( a blood collection chamber), the atrium, the ventricle (a pump), and the conus arteriosus (another pump).
  • Backbone - which is sometimes made of cartilage and sometimes made of bone. Fish brains are encased in a skull.
  • Fins - help fish swim in a similar way as a paddle helps us on a boat. Fins provide a large surface the fish can use to push against the water.
  • Reproduction - Most types of female fish lay eggs that are fertilized by the male, by a cloud of sperm cells, once the female releases the eggs from her body. This is not true for all types of fish though/ The eggs of sharks, for example, are fertilized while they are still in the mother's body, and begin their development within her body, being born when they are mature enough to live on their own.

Fish? Or Fishes?

Did you know that if you are talking about several of the same kind of fish it's correct to say "fish," but if you are talking about several different species, it's correct to say, "fishes?" That's why biology textbooks refer to the "Fishes of the Amazon River."

3 Classes of Fish

Jawless fish, Cartilaginous fish, Bony fish.

Jawless fish


Jawless fish have no jaws, no scales, and no bones. Their mouths contain structures for sucking, scraping, or stabbing their food. Their skeletons are made of cartilage.

Hagfish | Source


  • Hagfish are one type of jawless fish.

    Hagfish look like large worms and are scavengers that eat dead fish.

    Hagfish have a couple of interesting defense mechanisms. They create slime and can tie themselves into a knot. When another fish tries to bite a hagfish, the hagfish gives off an enormous amount of slime, causing it's predator to release it to avoid choking on the slime! Being able to tie themselves into a knot also helps hagfish get away from predators!

Short Video of Hagfish Producing Slime and Tying Itself In A Knot

Lamprey | Source


  • Lamprey are another type of jawless fish.

    Some species of lamprey are parasitic, using their mouths as suckers to attach to other living fish. Once attached, they suck the blood of the larger fish. You can see a lamprey attached to a bigger fish in one of the drawings below.

    Although there are 38 species of Lamprey, only 18 of these are parasitic.

Lamprey attached to larger fish (top) Parts of a Lamprey (bottom)
Lamprey attached to larger fish (top) Parts of a Lamprey (bottom) | Source

See if you can identify the parts of this Lamprey (below). You can look at the labeled image above as a guide.

Lamprey | Source

Cartilaginous fish - Sharks, Rays, and Skates

Whale Shark
Whale Shark | Source

Cartilaginous fish have jaws, rough scales, and skeletons made out of cartilage and calcium carbonate. Their skeletons are light and strong. Sharks, rays, and skates are all cartilaginous fish..

Grey Reef Shark
Grey Reef Shark | Source


Sharks have an excellent sense of smell because the part of their brain associated with smell is twice as large as other parts of their brain. This allows sharks to detect a tiny drop of blood in 25 gallons of water!

Most sharks rely on swimming or water currents to keep water passing over their gills. They must even take care to position themselves in a current while they are sleeping / resting.

Sharks have cone-shaped scales which are very similar in structure to their teeth. They have 6 to 10 rows of teeth, with the sharp, mature teeth in the front rows and immature teeth growing behind them. The teeth in the back move forward to replace the front teeth, as needed, operating almost like a conveyor belt.. A shark may lose 30,000 or more teeth over the course of his lifetime!

Manta Ray
Manta Ray | Source

Rays and Skates

Rays and Skates are graceful flatfish that almost seem to fly like birds through the water. When they are not swimming, they often bury partially under the sand on the ocean floor.

Rays and Skates have tails. The tails of some types of rays, such as those of a stingray, have barbed stings and venom glands on them. Stingrays use their tails only in self defense.

Watch this beautiful Manta Ray as she swims over a reef.

National Geographic Documentary on Stingrays

Bony Fish - Bony fish are what you probably think of when you think of a fish!

Flounder, bass, and trout are a few of the many kinds of bony fishy.

Bony Fish Have:

  1. Skeletons made of bones.
  2. Lateral line system - a sensory system along the sides of a fish's body. It helps the fish perceive its rate of movement through the water as well as its position. A fish's lateral line system can also help it detect a motionless object. Similarly to the way our inner ear works, the cilia on a fish's sensory cells detects vibrations and passes that information on to the brain.
  3. Operculum - These can open and close over the gills, producing a cover. These gill covers allow the fish to move water over its gills even when the fish is not moving.
  4. Swim Bladder - This is a gas sack which keeps a fish from sinking. As the swim bladder fills with gas, the fish rises higher in the water. Likewise, as the swim bladder empties, the fish sinks.

Hector's lanternfish (A Type of Bony Fish)
Hector's lanternfish (A Type of Bony Fish) | Source

The anatomy of Hector's lanternfish (above)

A: dorsal fin

B: fat fin

C: caudal fin

D: anal fin

E: pelvic fins

F: pectoral fins

G: operculum (gill cover)

H: lateral line

I: caudal peduncle

J: photophores

There are two groups of Bony Fish

Ray Finned Fish
Ray Finned Fish | Source

Ray-Finned Fish and Lobe-Finned Fish are the two groups of bony fish. Shown here is a Ray-Finned Fish. Here are the parts of a Ray-Finned Fish.

A: lateral line

B: kidney

C: swim bladder

D: Weberian apparatus

E: inner ear

F: brain

G: nostrils

H: internal sex organs (ovaries or testes)

I: spleen

J: gall bladder

K: stomach

L: heart

M: gills

N: eye

O: dorsal fin

P: fin rays

Q: tail (caudal fin).

R: anal fin

S: spine

T: ventral fins

Comments? Questions?

    0 of 8192 characters used
    Post Comment
    • LisaDH profile image


      5 years ago

      The diversity in fish is amazing. It seems strange to think that seahorses, rays and sharks are all fish. But then again... horses, moles and bats are all mammals, and they're pretty diverse, too.

    • TonyPayne profile image

      Tony Payne 

      5 years ago from Southampton, UK

      Wow that was really interesting information. I have seen a lot of fish in my time, mostly when snorkeling and diving in a lot of locations, but I never thought so much about the different types.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)
    ClickscoThis is a data management platform studying reader behavior (Privacy Policy)