Chapter 14.2 Fish

Fish Characteristics All fish are ectotherms. They can live in any water habitat. Some fish have the ability to live part of their life in fresh water and part in salt. Most fish can move quickly because they have a muscular tail and fins. Fins are fanlike structures used for steering, balancing, and moving. Paired fins on the left and right of the fish allow them to move right, left, backward, and forward. Fins on the top and bottom give stability. Most fish have scales, which are hard, then plates that cover the skin and protect the body. Scales can be different shapes.

Body Systems All fish have highly developed sensory systems. They will have a lateral line system that is made of a shallow, canal-like structure that is along the length of the fish’s body and filled with sensory organs. This allows the fish to sense it’s environment and detect movement. Sharks have a strong sense of smell. Fish have a 2-chambered heart.

Gas Exchange Most fish have gills that exchange carbon dioxide and oxygen.

Feeding Adaptations Some fish are filter feeders. Some fish eat other fish. Most fish do not chew their food.

Reproduction Fish reproduce sexually. They have sex hormones that are controlled by environmental factors like temperature, length of daylight, and availability of food. Fish will release large amounts of eggs into the water and then sperm is released into the water to fertilize the eggs.

Jawless Fish Lampreys and hagfish are in this group. They have round, toothed mouth, and long bodies. They do not have scales, but have a very slimy skin. Most are parasites that feed on blood or body fluids. Their skeletons are made of cartilage.

Jawed Cartilaginous Fish This group contains sharks, skates, and rays. They have an endoskeleton made of cartilage. They have moveable jaws with well developed teeth. They have tiny scales on their skin that feel like sandpaper. Sharks are the top predators in the ocean.

Bony Fish These are fish with skeletons made of bone. They have a swim bladder – it is an air sac that allows the fish to move up and down in the water. It changes the density of the fish. When the swim bladder inflates the fish rises in the water. As the swim bladder deflates the fish will sink in the water. Deep water fish will have oil instead of air so that it stays at a certain depth.

Lobe-Finned Fish These fish have lobelike and fleshy fins. There are just a few lobe finned fish living.

Lungfish This fish has lungs and gills. They can live in shallow water with little oxygen. When there is not enough water the lungfish will burrow in the mud and cover themselves with mucus until there is water again.

Ray-Finned Fish These fish have fins made of long, thin bones covered with skin. Most fish we are familiar with are ray- finned fish.