Fish that do not have scales include catfish, sharks, rays, chimaeras, skates, moray eels, sturgeons, paddlefishes, salifin blennies, combtooth blennies, hagfishes and lampreys. Many of these fish have evolved scale alternatives.
Cartilaginous fishes like sharks and rays not only lack scales, they also lack bones. Their skeletons consist of cartilage, which is flexible and allows some of them to grow to enormous size. The whale shark is the largest fish on earth and can grow to 30 feet long. The manta ray is also a huge animal that can be over 22 feet across and weigh over 3,000 pounds. Instead of the scales that other fish possess, these fish have denticles, which are basically tiny teeth that make their hides feel like sandpaper.
Sturgeons are fish that have scutes instead of scales. These are bony plates that are more often seen in crocodilians. They can also grow to a great size and live to a great age. The average lifespan of the lake sturgeon is about 82 years.
Lampreys are primitive fish. They have round, jawless mouths lined with rows of teeth. Some are parasites that grab on to another fish with their mouths, rasp a hole in the flesh and feed on bodily fluids.