Catfish, sharks, rays, chimaeras, skates, moray eels, sturgeons, paddlefishes, salifin blennies, combtooth blennies, hagfishes, and lampreys are examples of scaleless fish. Numerous of these species have evolved alternate scales.
Cartilaginous fishes, such as sharks and rays, lack not only scales but also bones. Their cartilage-based skeletons are flexible, allowing some of them to attain huge sizes. The whale shark has a maximum length of 30 feet and is the largest fish on earth. The manta ray has a maximum width of about 22 feet and a maximum weight of over 3,000 pounds. Instead of scales, these fish have denticles, which are essentially tiny teeth that give their hides a sandpaper-like texture.
Sturgeons are fish with scutes rather than scales. These are the bone plates typically observed on crocodiles. They can also attain tremendous size and longevity. The typical lake sturgeon lifespan is approximately 82 years.
Lampreys are primitive fish. They have mouths that are spherical, jawless, and lined with rows of teeth. Some are parasites that attach themselves to other fish with their jaws, make a hole in their flesh, and feed on their bodily fluids.