Teleost

Teleostei, also known as teleosts, are the largest group of ray-finned fishes, making up 96% of all fish species alive today. They include over 26,000 different species arranged in about 40 orders and 448 families. These fish come in many shapes and sizes, from the giant giant oarfish that can be more than 7.6 meters long, to the tiny male anglerfish Photocorynus spiniceps, which is only about 6.2 millimeters long. Teleosts can be torpedo-shaped for speed, flattened, elongated, or even have very special shapes like seahorses.

What makes teleosts different from other bony fish is their special jaw structure. They have a movable premaxilla that allows them to protrude their jaws outwards from the mouth. This helps them grab prey and draw it into the mouth. In many teleosts, the upper and lower parts of the tail (caudal) fin) are about the same size, and their spine ends at the caudal peduncle.

Teleosts have many ways of having babies. Most lay eggs that are fertilized outside the body, and the young, called larvae, grow up without any more help from their parents. Some teleosts start life as females and later change into males. A few give birth to live young and some parents, usually males, guard the eggs and keep them safe.

These fish are very important to people. They are caught for food, caught for sport by anglers, and some are farmed. Others are kept in aquariums or used in scientific research, especially in genetics and developmental biology.

Anatomy

Main articles: Fish anatomy and Fish jaw

Teleosts, or modern bony fishes, have special features that help them catch food. One key feature is a movable part called the premaxilla, which helps them suck prey into their mouths by lowering pressure inside. Their lower jaws then close to hold the food tightly.

These fish also have a second set of jaws inside their throats called pharyngeal jaws, made from bone loops that support their gills. In more advanced teleosts, these jaws help grind food as well as move it. The tail fin of teleosts is homocercal, meaning the top and bottom parts are about the same size, and their bones are lighter, making them quicker and more flexible than older bony fishes.

Evolution and phylogeny

Main article: Evolution of fish

The teleosts, a large group of ray-finned fishes, were first identified in 1845 by German ichthyologist Johannes Peter Müller. The name comes from Greek words meaning "complete" and "bone." Their fossils date back to the Triassic period, but they likely evolved earlier during the Paleozoic era. Teleosts diversified greatly during the Mesozoic and Cenozoic eras, making up 96% of all living fish species today.

Teleosts have evolved in many ways to live in different water environments. They range from very large fish like the giant oarfish to tiny species like the male anglerfish. Some teleosts have special shapes to help them move quickly through open water, while others have bodies that let them twist and turn easily in reefs. Certain teleosts can even produce electric currents to find or stun their prey.

Distribution

Teleosts are found all around the world in many types of water, from warm and cold seas to freshwater rivers and lakes. Some even live in very special places, like the desert pupfish, which survives in hot, salty water in deserts. However, there are fewer types of teleosts in very cold places, such as near Franz Josef Land.

Many groups of teleosts live in both salty and fresh water, but some prefer just one type. For example, salmon are found in both fresh water and the sea, and they travel between the two to lay their eggs. Other fish, like the European eel, live in the sea as adults but travel far to breed in the Sargasso Sea before their young return to Europe. Teleosts can also live in very high mountains or very deep ocean trenches.

Physiology

Further information: Fish physiology

Teleosts, like most fish, breathe by moving water over their gills to exchange gases. They need to keep breathing continuously because they don’t store oxygen in their bodies. Some teleosts live in places with little oxygen, like muddy water, and have special ways to get air, such as breathing through their skin or using extra organs to breathe air directly.

Teleosts have excellent senses. Most can see colors as well as humans, and they have special cells to detect smells and tastes. They also have a system called the lateral line that feels movements and vibrations in the water, helping them find food and avoid danger. Some fish can even sense electrical fields or Earth’s magnetic field to navigate.

Fish cannot control their own temperature like humans; their body temperature matches the water around them. Most can only survive in a limited temperature range. Some fish, like tuna, have special ways to keep their muscles warmer to swim faster in cold water.

Teleosts use a special organ called the swim bladder to help them stay at one depth in the water without constantly swimming up or down. The swim bladder changes the amount of gas inside to make the fish lighter or heavier as needed.

Main article: Fish locomotion

Most teleosts swim by moving their bodies sideways in a wave-like motion, pushing themselves forward. However, some fish move differently depending on where they live. For example, eels wiggle their whole bodies, while seahorses flutter their fins to move slowly among seaweed. Some fish, like flying fish, can leap out of the water and glide through the air using their large pectoral fins.

Reproduction and lifecycle

Further information: Fish reproduction

Most teleost fish species lay eggs and release them into the water where they are fertilized by sperm. This is called external fertilization. In a few species, fertilization happens inside the body. For those that lay eggs, very few survive to become adult fish. Some species give birth to live young, which increases the chances of survival for the babies. These fish keep their eggs inside until they are ready to hatch, either inside the mother or in special places like nests.

Teleost fish have two main ways of reproducing. In one way, called semelparity, a fish breeds only once and then dies. This happens in salmon, which travel from the ocean back to their birthplace to spawn and then pass away. In the other way, called iteroparity, a fish can breed many times during its life. Most teleost species use this method.

Sex identity and determination

Most teleost species have males and females that stay that way their whole lives. Whether a fish is male or female can be decided by genes, like in humans, or by the environment, like temperature. In some species, both genes and environment decide the sex. For example, in some fish, warmer water creates more males, while cooler water creates more females.

Some teleost species can change their sex during their lives. This is called hermaphroditism. In these species, a fish might start as one sex and then change to the other later. For example, in clownfish, if the largest female dies, the largest male changes into a female so the group can continue to reproduce.

Mating tactics

Teleost fish have different ways of finding mates. Some species, like guppies, have many partners. Others form pairs and stay together. Some males guard groups of females, while others display to attract mates. In some species, males develop special features to help them attract females, like bright colors or bigger heads.

Spawning sites and parental care

Teleost fish lay their eggs either in the water or on surfaces like rocks or plants. Most do not take care of their young after they lay eggs. However, some species do care for their young. For example, some fish carry their eggs in their mouths until they hatch. Others build nests to protect their eggs. In some species, the young help take care of newer babies, cleaning and protecting them.

Growth and development

Teleost fish go through several stages in their lives: egg, larva, juvenile, and adult. When they first hatch, they look very different from adults and cannot swim well. As they grow, they change shape and develop features like scales and fins. By the time they become juveniles, they look more like adults and can swim and find food. Finally, as adults, they can reproduce. Some teleost fish live for many years, with some species living over 100 years.

Shoaling and schooling

Main article: Shoaling and schooling

Many teleost fish form groups called shoals, which help them stay safe and find food more easily. By staying together, these fish can watch for predators better and work as a team to catch food. When a danger appears, they move together in coordinated ways to protect themselves. Sometimes they scatter and then come back together. Fish also come together in groups to lay their eggs.

Relationship with humans

Main article: Fish in culture

Teleosts are important to humans in many ways. They are caught for food worldwide, with species like herring, cod, pollock, anchovy, tuna, and mackerel providing millions of tons of food each year. Many people also enjoy fishing for sport, and both commercial and recreational fishing create jobs for millions.

Some teleosts, such as carp, salmon, tilapia, and catfish, are farmed commercially, producing lots of food. Fish can be eaten fresh or preserved using methods like drying, smoking, salting, fermentation, and pickling. Modern ways to keep fish include freezing, freeze-drying, and canning. Some smaller, colorful teleosts make great aquarium pets.

Teleosts have also inspired artists for thousands of years. They appear in ancient art from Ancient Egypt to modern paintings. Artists like Vincent van Gogh and Ernst Haeckel have created beautiful works featuring these fishes.