Teleost

Most fish are teleosts.

There are over 26,000 kinds of them. Some are very big. Some are very tiny.

These fish have special jaws. Their jaws can move out from their mouth. This helps them grab food. It sucks the food inside.

They come in many shapes. Some are long like a tube. Some are flat. They can be fast swimmers.

Many fish lay eggs in the water. Some fish stay to guard the eggs. This keeps the babies safe.

People catch these fish for food. We also keep some in tanks. They are very important to us.

Most fish in the world are teleosts. They make up 96% of all living fish species. There are over 26,000 kinds of them.

Teleosts come in many shapes. Some are long like a tube. Others are very flat. Some are even tiny. The giant oarfish can grow very long. The ocean sunfish is very heavy.

These fish have special jaws. The top part of the jaw is the premaxilla. This bone can move out from the mouth. This helps the fish suck in food. It also helps them grab prey.

Their tails also look different. The top and bottom parts of the tail are equal in size. This is called a homocercal tail.

Many teleosts lay eggs in the water. Most fish do this. The male and female do not always help the babies. Some males guard a nest. They fan the eggs to keep them healthy. People catch teleosts for food. We also study them to learn about life.

Teleosts are a massive group of ray-finned fishes. They make up 96% of all living fish species today. This group includes over 26,000 different species. They are found in many different orders and families. You might see them in a local pond or the deep ocean. They are very important to humans for food and science.

These fish have a very special way of eating. Their upper jaw bone is called the premaxilla. This bone is not attached to the braincase. It can move outward from the mouth to create a hole. This action lowers the pressure inside the mouth. It works like a vacuum to suck prey inside. Then the jaw closes to grasp the food tightly.

Scientists have studied these fish for a long time. A German scientist named Johannes Peter Müller first named them in 1845. His name for them comes from Greek words meaning "complete bone." Later, in 1966, researchers named Greenwood and others gave a better classification. They looked at how these fish are related. We now know they have changed a lot over millions of years.

Teleosts have many different shapes and sizes. The giant oarfish can grow very long. The ocean sunfish can weigh over a thousand pounds. Some, like the male anglerfish, are just one inch long. Their tails are also unique and called homocercal. This means the top and bottom parts of the tail are equal. The spine ends at the base of the tail.

Many things in our world connect to teleosts. People catch them for sport or for food. Some fish are even raised on farms. Scientists use them to study genetics and how life develops. You might even see them in an aquarium. They are a huge part of our planet's oceans and rivers.

Teleostei, commonly known as teleosts, represents the largest group of ray-finned fishes within the class Actinopterygii. These fish are incredibly diverse, making up approximately 96% of all living fish species on Earth today. The group contains over 26,000 species organized into about 40 orders and 448 families. Because they are so widespread, they occupy almost every aquatic environment. They range from the massive ocean sunfish, which can weigh over 2,000 pounds, to the tiny male anglerfish, *Photocorynus spiniceps*, which measures only one inch long.

The most significant physical difference between teleosts and other bony fish is their specialized jaw structure. Teleosts possess a movable premaxilla, which is the bone at the very front of the upper jaw. This bone is not attached to the neurocranium, or the braincase. When the fish feeds, the maxilla acts as a lever to push the premaxilla outward. This creates a circular opening that lowers the pressure inside the mouth. This mechanism works like a vacuum to suck prey into the mouth.

By using this suction, teleosts can grab prey without the risk of pushing it away by simply closing their jaws. In more advanced species, the premaxilla is the main bone that holds teeth.

Beyond the outer mouth, teleosts have a second set of jaws located in the throat called pharyngeal jaws. These are composed of five branchial arches, which are bony loops that support the gills. In more basal, or primitive, teleosts, these jaws mainly serve to transport food. However, in more derived teleosts, these structures have become much more powerful. The left and right ceratobranchials fuse to form a single lower jaw. These pharyngeal jaws also include specialized muscles that allow the fish to grind their food before swallowing.

Teleosts also feature a specific tail structure known as a homocercal caudal fin. In a homocercal tail, the upper and lower lobes are roughly equal in size. This differs from many other fish where the spine extends into the upper lobe of the tail. In teleosts, the spine ends at the caudal peduncle, which is the narrow base of the tail. To support the upper lobe, they have elongated neural arches called uroneurals. This skeletal arrangement contributes to the flexibility and speed seen in many species.

The history of teleost classification began with the German ichthyologist Johannes Peter Müller in 1845. He named the group after the Greek words *teleios*, meaning "complete," and *osteon*, meaning "bone." While Müller focused on soft tissue, modern scientists use DNA to understand their true relationships. In 1966, researchers including Greenwood provided a more stable classification system. We now know that while the oldest stem groups appeared in the Triassic period, teleosts likely began evolving during the Paleozoic era. They saw a massive increase in size and abundance following the Cretaceous-Paleogene mass extinction about 66 million years ago.

Within the teleost family, there are several distinct lineages with unique adaptations. The Elopomorpha, which includes eels, have thin, leaf-shaped larvae called leptocephali. The Osteoglossomorpha, or elephantfishes, are defined by a unique bony element in their tongue. Another major group, the Ostariophysi, includes many freshwater fish like carps and catfishes. These fish possess a Weberian apparatus, which is a series of bones connecting the swim bladder to the inner ear. This allows them to hear much better by transporting vibrations from the bladder to the ear.

Teleosts are also highly significant to human society and global economies. The fishing industry harvests many species for food, and many others are raised on commercial farms. Some people catch teleosts for sport, while others keep them in aquariums for beauty. Beyond food and hobbies, they are vital to the scientific community. Researchers use teleosts in the fields of genetics and developmental biology to understand how life works. Their ability to adapt to so many different roles makes them a central part of the Earth's biological systems.