Fish are a diverse group of aquatic animals that are classified into several major classes based on their anatomy, physiology, and evolutionary history. The main classes of fish are:
- Agnatha: Jawless fish, such as lampreys and hagfish, characterized by their lack of jaws and paired fins. They have elongated, eel-like bodies and a primitive vertebrate structure.
- Chondrichthyes: Cartilaginous fish, including sharks, rays, and skates. Their skeletons are made of cartilage rather than bone, and they typically have well-developed jaws, paired fins, and rough, sandpaper-like skin.
- Osteichthyes: Bony fish, which make up the majority of fish species. They have skeletons made of bone, scales that cover their bodies, and a swim bladder for buoyancy. This class is further divided into two subclasses:
- Actinopterygii (ray-finned fish): Characterized by fins supported by bony rays. Examples include salmon, goldfish, and tuna.
- Sarcopterygii (lobe-finned fish): Possess fleshy, lobed fins with bone structures similar to those of terrestrial vertebrates. Examples include coelacanths and lungfish.
Amphibia are not a class of fish; the major fish classes are Agnatha, Chondrichthyes, and Osteichthyes.
Chondrichthyes, including sharks and rays, have a cartilaginous skeleton, unlike other fish classes.
Agnatha are jawless and have elongated bodies; they lack paired fins as well.
Osteichthyes have a bony skeleton, which sets them apart from other fish classes.
Osteichthyes include ray-finned and lobe-finned fish.
Lobe-finned fish have fleshy, lobed fins with internal bone structures.