Ray-Finned Fishes, Lobe-Finned Fishes, and Sharks!
The cartilaginous fishes are a group of about 1,000 species and share many things in common, including the presence of jaws, paired fins, a two-chambered heart, and bodies made of cartilage.
By far the largest group of fish are the bony fish. Eight species of bony fish make up a small group called lobe-finned fish, including the lungfish, a fish with the ability to breathe air, that can even drown if it is kept in water too long.
Another 27,000 species make up the ray-finned fish. Remember from above that there are a total of slightly less than 58,000 species of all vertebrates. It is clear that bony, ray-finned fish are the most common vertebrates.
The lungfish is one of only eight species of lobe-finned bony fish.
As with fish in general, bony fish vary greatly in size and weight, from the 3.3 meter (11 foot) ocean sunfish, topping the scales at over 5,000 pounds, to the tiny pygmy goby, a mere 1.5 cm (0.6 in).
In spite of the variation in size and weight, bony fish have several characteristics that group them together and make them unique amongst the fish.
First, these fish have the ability to regenerate bone from cartilage inside their body. Additionally, ray-finned fish are the only fish that can see in color. Finally, all members of this group have swim bladders, which they are able to add oxygen to or remove oxygen from. This allows the fish to control its density.
Why would a fish want to do this? As you may know, things that are more dense than the fluid they are in will sink, while things less dense than the fluid will float. By changing their density compared to the fluid they are in (water), a fish can cause itself to rise up higher or sink down lower as needed.
Here’s a short video of a puffer fish during its inflating and deflating stages:
There are a number of reasons why fish are important to humans. They provide a source of food, especially for people who live in areas near water. Fishing is also a popular recreational activity, and many people enjoy viewing these beautiful animals in aquariums every day. People have included fish, and legends of half-fish, half-human creatures in stories and legends since ancient times.
Fish are important to more than just humans however. The food web of the oceans and lakes of the world are some of the most diverse on the planet, and the wide variety of fish that live in these ecosystems play a crucial role in maintaining a balance. Humans have recognized this, and have begun to restrict fishing and recreational activities in areas where too much human activity could be harmful to the aquatic ecosystem.