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10.6: Bony Fish

Difficulty Level: At Grade Created by: CK-12
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Can fish have bones?

Of course. Many fish have bones. They serve the same function as our bones: protection and support. Notice how the skeleton protects the fish's brain. Also, notice the bones along the body of the fish would allow muscles to attach to aid in movement.

Bony Fish

There are about 27,000 species of bony fish (Figure below), which are divided into two classes: ray-finned fish and lobe-finned fish. Most bony fish are ray-finned. These thin fins consist of webs of skin over flexible spines. Lobe-finned fish, on the other hand, have fins that resemble stump-like appendages.

Fins of bony fish: ray fin (left) and lobe fin (right).

Characteristics of Bony Fish

Most fish are bony fish, making them the largest group of vertebrates in existence today. They are characterized by:

  1. A head and pectoral girdles (arches supporting the forelimbs) that are covered with bones derived from the skin.
  2. A lung or swim bladder, which helps the body create a balance between sinking and floating by either filling up with or emitting gases such as oxygen.
  3. Jointed, segmented rods supporting the fins.
  4. A cover over the gill called the operculum, which helps them breathe without having to swim.
  5. The ability to see in color, unlike most other fish.
Ray-finned Fish

The ray-finned fish have fin rays, with fins supported by bony spines known as rays. The ray-finned fish are the dominant class of vertebrates, with nearly 99% of fish falling into this category. They live in all aquatic environments, from freshwater and marine environments from the deep sea to the highest mountain streams.

Lobe-finned fish

The lobe-finned fish are characterized by fleshy lobed fins, as opposed to the bony fins of the ray-finned fish. There are two types of living lobe-finned fish: the coelacanths and the lungfish. The pectoral and pelvic fins have joints resembling those of tetrapod (four-limbed land vertebrates) limbs. These fins evolved into legs of amphibians, the first tetrapod land vertebrates. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of ray-finned fish. All lobe-finned fishes possess teeth covered with true enamel.

How Big Are Bony Fish?

The ocean sunfish is the most massive bony fish in the world, up to 11 feet long and weighing up to 5,070 pounds (Figure below). Other very large bony fish include the Atlantic blue marlin, the black marlin, some sturgeon species, the giant grouper, and the goliath grouper. The long-bodied oarfish can easily be over 30 feet long, but is not nearly as massive as the ocean sunfish. In contrast, the dwarf pygmy goby measures only 0.6 inches. Fish can also be quite valuable. In January 2013, at an auction in Tokyo's Tsukiji fish market, a 222-kilogram (489-pound) tuna caught off northeastern Japan sold for 155.4 million yen, which is $1,760,000.

An ocean sunfish, the most massive bony fish in the world, can reach up to 11 feet long and weigh up to 5,070 pounds!


  • operculum: A hard bony flap covering and protecting the gills.
  • pectoral girdles: Bony structure supporting the fins.
  • swim bladder: Gas-filled organ that helps a fish to control its buoyancy.


  • The bony fish are divided into two classes: ray-finned fish and lobe-finned fish.
  • The bony fish are characterized by a lung or swim bladder, a cover over the gills, and bones covering the head and pectoral girdles.


Use the resources below to answer the questions that follow.

  1. What is one of the purposes of the operculum?
  2. What is the lateral line used for? Where is it located?
  3. Not all fish have swim bladders, but, for those who do, what are they used for? Why do you think some fish don't have swim bladders?
  1. What family do seahorses belong to?
  2. What is unusual about seahorse reproduction?
  3. How wide is a seahorse's field of vision? How is it so wide?
  4. What do seahorses feed on? How are their jaws adapted to their prey?


  1. What characterizes the bony fish?
  2. What are the two classes of the bony fish?

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A hard bony flap covering and protecting the gills.

pectoral girdles

Bony structure supporting the fins.

swim bladder

Gas-filled organ that helps a fish to control its buoyancy.

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Difficulty Level:
At Grade

Concept Nodes:

7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Aug 30, 2016
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