Here Fishy FishyFish have had an evolution all their own. When you think of a fish today, you are actually thinking about an advanced organism. They started their development over 500 million years ago as fish-like organisms without jaws. Over many years they developed bones and skeletons. There are four main types of fish.
(1) Jawless fish: Like we just said, the first fish didn't have jaws. It is tough to eat and even harder to survive in the long run. Even with a mouth and a series of teeth to cling to their food, it's still hard to compete with fish that have jaws and mouths. Some species made it to the modern world. One good example is a Lamprey. These fish suck on the sides of other fish. Not a very exciting life.
(2) Fish with cartilage: In our opinion, though not as advanced as fish with real bones, fish with cartilage are the coolest fish out there. Cartilaginous fish include species of sharks, rays, and skates. Sharks are the ultimate hunters of the ocean. They are big, fast, and have very sharp teeth that rip their prey apart. Skates and rays are a lot more docile or non-aggressive. They are usually bottom feeders. The bodies of rays and skates have developed large wings that allow them to glide through the water using their tail as a rudder.
(3) Bony fish with lobe fins: And then the fish with real bones came along. No longer was cartilage the skeleton of choice. Bony fish were able to out-compete most of the fish that had cartilage for skeletons. Scientists classify them into two groups - the LOBE-finned and the RAY-finned. Lobe-finned bony fish include examples such as lungfish and coelacanthus. Until about 30 years ago, scientists thought the coelacanthus was long extinct. One day a fisherman found one in the net and voila!
(3) Bony fish with ray fins: You probably think of these fish when you think of a classic fish. The bony fish with ray shaped fins include goldfish, tuna, and trout, all tasty fish you can eat. Goldfish are for the college guys. They have complex skeletons and are built to move. Some move really fast and are very strong. Something like a tuna can move extremely quickly through the water.
Science Nation: Waterfall Climbing Fish (US-NSF Video)
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