Fish are a diverse group of aquatic animals that have been around for over 500 million years. They come in a staggering variety of shapes, sizes, and colors. Broadly speaking, they can be classified into three main categories:
Jawless Fish (Agnatha): These are the most primitive type of fish, including lampreys and hagfish. They lack jaws and paired fins.
Cartilaginous Fish (Chondrichthyes): These fish have a skeleton made of cartilage rather than bone. This group includes sharks, rays, and skates. They typically have jaws and paired fins.
Bony Fish (Osteichthyes): This is the largest group of fish, with a skeleton made of bone. They are further divided into two main groups:
- Ray-finned Fish (Actinopterygii): This is the most diverse group, including species like salmon, tuna, and goldfish. They have fins supported by bony rays.
- Lobed-finned Fish (Sarcopterygii): This group includes coelacanths and lungfish. They have fleshy, lobed pectoral and pelvic fins, which are more similar to the limbs of land vertebrates.
Fish play crucial roles in aquatic ecosystems, from maintaining the health of coral reefs to influencing the structure of aquatic communities. They are also a major food source for humans and are an important part of many cultures and economies.
