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Facts About Fishes


Great barracuda - Sphyraena barracuda

Great barracuda - Sphyraena barracuda

Photo © Daj / Getty Images.

In this article, you'll learn interesting facts about fishes and find out about their unique characteristics, their life cycle and their evolutionary history.

FACT: Fishes are divided into three basic groups which include cartilaginous fishes, bony fishes, and lobe-finned fishes.

Cartilaginous fishes are so named because instead of bony skeletons, their body frame consists of cartilage. Tough and flexible, cartilage provides enough structural support to enable these fish to grow to incredible sizes. Cartilaginous fishes include sharks, rays, skates and chimaeras.

Ray-finned fishes are the most diverse of the three groups of fishes. The group includes mor than 23,000 species such as salmon, trout, lanternfish, cavefish, cods, anglerfish, tarpon, herrings, electric eels and many others. In contrast to cartilaginous fishes, the skeletons of ray-finned fishes are composed of true bone.

Lobe-finned fishes are a group of bony fishes that have paired fins that are at their base fleshy lobes. Ancient lobe-finned fishes are thought to be the ancestors of the first four-legged land vertebrates or tetrapods. Modern lobe-finned fishes include lungfish and coelacanths.

FACT: Fishes were the first animals to evolve backbones.

The earliest known fishes were the ostracoderms, a now-extinct group of jawless fishes that appeared in the Cambrian Period, about 510 million years ago. These primitive fishes had a notochord but no jaw bones or teeth. Other early fish-like animals include the conodonts and the agnanthans (the hagfish and the lamprey).

FACT: The ray-finned fishes are the largest group of fish.

There are nearly 24,000 species of ray-finned fishes which are divided into 431 families.

FACT: Some species of fish migrate between freshwater and marine environments to spawn.

Such species are referred to as diadromous. They are further described by the direction of their migration. Fish that migrate from the sea into freshwater rivers to spawn (for example, salmon) are described as anadromous. Fish that migrate from a freshwater environment to the sea to spawn (for example, freshwater eels) are described as catadromous.

FACT: Fishes move by creating a wave motion that moves the length of its body.

This wave motion begins at the head and moves to the tale where the resulting side to side motion produces thrust to move the fish through the water.

FACT: Fishes are cold-blooded (ectothermic) animals.

Their internal body temperature is therefore the same as the surrounding water.

FACT: Many species of cichlids brood their eggs in their mouth.

After the eggs hatch the parent continues to use their mouth to provide shelter for their young.

FACT: There are two groups of jawless fishes alive today.

Once a diverse group of fish that appeared over 500 million years ago, jawless fish are today represented only by lampreys and hagfish.

FACT: Cartilaginous fish include the sea's largest and most skilled marine predators.

These include sharks, skates, rays, and chimeras. These fish have skeletons made from cartilage, not bone. The cartilaginous skeletons are more flexible than bone.

FACT: The lateral line system on some fish detects variations in water pressure.

This helps fish detect prey and avoid predators.

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