Learn about the circulatory system of Osteichthyes, a class of chordates that includes all bony fishes. Osteichthyes is the largest class of vertebrates, with over 28,000 species, but you may be surprised to find out just how similar they are to us!
What are Bony Fish?
Even if the class Osteichthyes isn’t familiar to you, the members of the class certainly will be. Osteichthyes is the largest class of vertebrates, with over 28,000 species of fish.
The majority of the fish that humans eat are members of Osteichthyes, so they are both an interesting and economically important group of animals.The name of the group is derived from the Greek osteon meaning bone, and ikhthus meaning fish. So while it makes little sense to us in English, in Greek it makes perfect sense. All members of this class of fish have bony skeletons, as opposed to cartilaginous skeletons which are seen in sharks.
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What Does a Circulatory System do?
Before we consider a fish’s circulatory system, we should be sure we know what a circulatory system is. A circulatory system is the system responsible for the circulation of blood, nutrients, and gases around an organism’s body. It is the circulatory system that helps maintain homeostasis, or the body’s overall chemical and temperature balance.In humans, our circulatory system is largely regulated by our heart, and works in conjunction with our cardiovascular system. As you will soon see, fish that are members of Osteichthyes have circulatory systems that are rather similar to our own.
The Osteichthyes Circulatory System
You can easily picture how your circulatory system works, but what about the circulatory system of a bony fish? There are many similarities, which include:
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- A closed system. That is, the circulatory system is comprised of one main loop, with blood, gases, and nutrients traveling between the heart, gills (lungs in humans), and body cells in a constant loop.
- The red blood cells act as the medium for gas exchange, moving oxygen into the cells and carbon dioxide out of the cells.
- Fish blood, like human blood, contains hemoglobin which gives it a reddish color, and coagulants to aid with clotting.
- White blood cells act as part of the immune system.
- Both circulatory systems have veins and blood vessels.
But we’re not fish, and there are some differences between their circulatory systems and ours. Some of the more notable differences include:
- The structure of the heart. Bony fish have a two chambered heart, whereas humans have a four chambered heart.
- The amount of body weight composed of blood, which is about 10% in humans but only about 2% in fishes.
- Instead of the well-developed lungs found in humans, fish have gills, which act to exchange gases with the outside world. However, a select few species do possess a simple set of lungs for breathing in oxygen-poor environments.
- Fish possess a structure known as a swim bladder, which may also be used for breathing in oxygen-poor environments, though it is mainly for regulating body position in the water.
