Bony Fish: Characteristics, Anatomy & Types

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  • 0:00 Classifying Fish
  • 1:00 Characteristics & Physiology
  • 3:07 Examples of Bony Fish
  • 3:53 Lesson Summary
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Lesson Transcript
Instructor: Meredith Mikell
Most of the world's fish are osteichthyes, meaning that they have bony skeletons. In this lesson, we will explore the definition, characteristics, anatomy, and some examples of bony fish.

Classifying Fish

On the outside, all fish pretty much look the same: they have streamlined bodies, scales, fins on their backs and sides, and a tail that moves side to side to propel them. But, if we look under the skin, we find some pretty important differences. Based on these differences, fish can be generally divided into two broad categories or classes based on their skeletal composition: chondrichthyes, or cartilaginous fish, including sharks, skates, and rays; and osteichthyes, or bony fish, including goldfish, piranha, sockeye salmon, and trout.

Bony fish have skeletons that are made up of hard, brittle, highly calcified bones - just like your own bones - whereas cartilaginous fish have skeletons that are made up of cartilage that is thin and flexible, just like the material that gives your nose its shape. In this lesson, we'll take a look at bony fish traits and anatomy and also see some examples, many of which you will likely recognize, of these diverse animals.

Characteristics & Physiology of Bony Fish

Bony fish not only have a hard, calcified skeleton, but a solid cranium protecting their brains as well. These animals depend upon their hinged jaw for feeding, a characteristic that distinguishes them from jawless fish, such as lampreys and hagfish. Bony fish also have unique ear plates called otoliths that help their sense of equilibrium and, when fossilized, provide scientists with lots of information about extinct bony fish species.

Bony fish are able to control their buoyancy using swim bladders, which are organs that take in dissolved gases from the water and then inflate or deflate accordingly. Speaking of dissolved gases, bony fish breathe by moving water across their gills using an operculum, which is a trapdoor-like structure that pumps water across the gills so that the fish can breathe without necessarily moving forward in the water.

Most bony fish have three pairs of gill arches, which are the bony structures that support the gills. They are made up of thin and bony gill filaments that increase the surface area for gas exchange, and in many cases, gill rakers that help fish strain tiny particles out of the water for feeding purposes.

The bodies of bony fish are covered with smooth scales that form an overlapping pattern and a thin layer of mucous that helps them move smoothly through the water. Bony fish are extremely well adapted to their environments, whether they live in freshwater or saltwater: they have paired fins for steering, dorsal fins for stability, and caudal fins for propulsion. And, like the vast majority of fish, they are ectothermic, or cold-blooded, meaning that they cannot generate their own body heat.

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