Fish and their habitats biology lesson for kids: 1st, 2nd, 3rd, 4th, 5th, 6th and 7th grades biology lesson.
Fish are a kind of aquatic animal, which means they live in water. They are vertebrates, animals that skeletons, especially backbones. Not every aquatic animal is a fish, though. How you know an animal is a fish is by looking at its body. All fish have gills and have limbs that don’t have any digits, finger-like points at the end.
Have you ever seen the word “fishes”? In everyday speech, it doesn’t really matter whether you use “fish” or “fishes” to refer to more than one fish, but, in biology, they mean two different things. For biologists, “fish” as a plural refers to more than one of a single species, or is a collective noun referring to fish in general. “Fishes”, though, refers to more than one specific kind or species of fish. So, you can say, “Fish live in water,” but you would say, “Bony fishes have scales.”
Fish use their gills to breathe. That means they use their gills to get oxygen from the water around them, and to get rid of carbon dioxide. They pull the water in through their mouths and push them out over the gills. The gills have lots of tiny blood vessels so the water can get as close to the blood as possible, since the blood is where the toxic carbon dioxide goes after the body makes it, and is how the fish’s body can send oxygen all around to all the cells that need it.
Believe it or not, some special fishes can breathe air! Some, like anguillid eels, use their skin to breathe. Others, called lungfish, have air sacs that work kind of like our lungs do, allowing them to survive in dry seasons when there isn’t much water around.
Another thing that fish have is scales. Fish scales tend to overlap and are hard so that they protect the skin and body of the fish. Many scales are easy to see, but some fishes, like sharks, have scales that are so small you can’t see them with your naked eye. You might think that all fishes have scales, but that’s not true. Some, like the clingfishes, don’t have scales. Instead, their skin is protected by a thin layer of mucous.
Fish reproduce in many ways. In most species, the females release lots of tiny eggs that the males fertilize. Some fishes, like carp and tuna, just lay the eggs and leave them to fend for themselves. Others, though, like the freshwater catfish, build nests for their eggs, and take care of them. Some fishes keep their eggs inside their bodies until they’re ready to hatch, and then the babies are born right from the mothers’ bodies!
This is just the tip of the iceberg when it comes to fish. There’s a whole lot more you can learn about these amazing animals.