Fishes

Ch.11.2

A Fish Story

• In the warm waters of a coral reef, a large spotted fish called a graysby hovers in the water, barely moving. A smaller striped fish called a goby swims up to the graysby. Then, like a vacuum cleaner moving over a rug, the goby swims slowly over the larger fish, eating dead skin and tiny parasites. The goby even cleans inside the graybsy’s mouth and gills. Both fishes benefit from this cleaning. They graysby gets rid of unwanted materials, and the goby gets a meal. Examples: click below

Goby Fish Human Another Human

Characteristics of Fishes

• A fish is a vertebrate that lives in water and uses fins to move.

• In addition to living in water and having fins, most fishes are:– Ectotherms– obtain oxygen through gills from water– and have scales.

• Fishes make up the largest group of vertebrates.

• Nearly half of all vertebrate species are fishes.

• They have also lived on Earth longer than any other kind of vertebrate.

Obtaining O2

• Fishes get their O2 from the water.

• As fish swim, they open and close their mouths to gulp water, passing it over their gills.

Circulatory System

• Fish have a closed circulatory system, like humans.

• This means the blood goes in a complete circle and starts again.

• The heart of a fish has 2 chambers.

Movement

• Fins help fishes swim.

• The fins act like canoe paddles and help them push against the water.

• They help a fish move and stay upright.

• Most fish have external fertilization.

Nervous System

• Most fish can smell and taste to find food.

• They also have a keen sense of touch. They can feel when something is moving near them.

• Some even have whiskers to feel.

Types of Fishes

• The major groups of fishes are:– Jawless Fishes– Cartilaginous Fishes– Bony Fishes

Jawless Fishes

• Jawless fishes are unlike other fishes in that they have no jaws AND NO SCALES!

• Sometimes, we call them “sucker-fishes.”

• Examples: Hagfishes and lampreys.

• Their skeletons are made of cartilage.

Cartilaginous Fishes

• The cartilaginous fishes have jaws and scales, and skeletons made of cartilage.

• The pointed, tooth-like scales that cover their bodies give their skin a texture that is rougher than sandpaper.

Obtaining O2

• Most sharks cannot pump water over their gills.

• Instead, they rely on swimming or currents to keep water moving over their gills.

• Rays and Skates are not as active as sharks. They spend a lot of time partially buried on the ocean floor.

• They take in water through small holes located behind their eyes.

Obtaining Food

• Cartilaginous fishes are usually carnivores.

• Rays and skates hunt on the ocean floor, crushing mollusks, crustaceans, and smaller fishes with their teeth.

• Sharks attack and eat nearly anything that smells like food.

• The mouth of a shark contains jagged teeth arranged in rows.

Bony Fishes

• A bony fish has jaws, scales, and a pocket on each side of the head that hold the gills, and a skeleton made of hard bones.

• They also have a swim bladder.

• A swim bladder is an internal, gas-filled sac that helps the fish stay stable at different depths in the water. It acts like a fish floaty!

An Exception To The Rule

• Mudskippers