Fish Characteristics

Internal fertilization

The male fish deposits the sperm inside the female. Usually, the female lays fertilized eggs that have embryos inside, but sometimes the embryos develop within the female.

Fins

A fan-shaped structure that helps to move and is used to steer, stop, and balance.

Swim bladder/Gas bladder

A balloon like organ that is inflated by oxygen and other gases that are lighter than water. It is used to control buoyancy and to keep the fish from sinking.

Scales

A bony structures that protects the body and lower friction as the fish swims through the water.

Lateral line

A faint line visible on both sides of a fish's body made of tiny sense organs that detect water vibration.

Gill

A organ that removes oxygen from the water that is exchanged with carbon dioxide from the fishes blood.

Ray-finned fishes

Almost all bony fish are ray-finned fishes. These fishes have paired fins supported by thin rays of bone. They include eels, herrings, trout, minnows, and perch.

Bony fishes

Bony fishes are different from all others fishes, they have a skeleton made of bone and their bodies are covered by bony scales. Bony fishes can also rest in one place without swimming and have a swim bladder which keeps them from sinking.

Lobe-finned fishes

Lobe-finned fishes have fins that are muscular and thick. There are seven living species of lobe-finned fishes and six of these are lungfishes. Lungfishes have air sacks that can gulp air, similar to lungs.

External fertilization

The female fish lays unfertilized eggs, and the male drops sperm on them. Most fish use this process of fertilization.

Jawless fish

These fish do not have a jaw. Jawless fish do not have jaws to eat, instead they use other ways, such as sucking the blood of other animals. Characteristics of a modern jawless fish is smooth, slimy skin and a round, jawless mouth.

Cartilaginous fishes

Unlike most vertebrates, these fishes skeletons never change from cartilage to bone. For example, the shark, skates, and rays.