17.2 FISHESPage 348

Gills

Organs that remove dissolved oxygen from water

Located on either side of fish’s head

Gills

How Gills Work

Water passes over gills as a fish swims

Oxygen in the water diffuses into cells at the surface of the gills

As this happens, carbon dioxide diffuses out of blood vessels into the water

Characteristics of Fish

All fish are ectotherms Most have streamlined bodies

and use fins for movement Most have excellent sense of

smell All have highly developed

nervous systems

3 Classes of Fish

1. Jawless Fish {Agnatha}

2. Cartilaginous Fish {Chondrichthyes}

3. Bony Fish {Osteichthyes}

Jawless Fish

Vertebrates (have backbone) Lack jaws Probably filter feeders Only a few species exist today

› Lampreys & Hagfish Parasites – their mouth is a sucker used to

attach to “hosts” and feed

Jawless Fish

LAMPREY

HAGFISH

Cartilaginous Fish

Cartilage: firm, but flexible, connective tissue

Cartilaginous fish have skeletons made completely of cartilage

Have jaws Most are carnivores – sharp teeth &

senses Some are filter feeders (whale shark)

Cartilaginous Fish

Some are filter feeders (whale shark) Bodies are more dense than water –

must keep swimming to stay off ocean floor

Swimming also creates current of water which passes over gills – supplies fish with oxygen

Cartilaginous Fish Examples

STINGRAY

SHARK

WHALE SHARK

Bony Fish

Greatest number of fish belong to this class

Have skeletons made of bone

Bony Fish Examples

SALMON

CATFISH

GOLDFISH

Bony Fish Anatomy

1. Swim Bladder Helps conserve energy Similar to a balloon Used to adjust their depth Inflating the bladder with right amount of

air keeps fish from sinking

Bony Fish Anatomy

Buoyancy

Buoyancy: force of liquid pushing an object up

If the weight of an object…. Is greater than the buoyant force, it will

sink Is less than buoyant force, it will float Is equal to the buoyant force, it will

stay at any level (FISH)

Buoyancy IllustratedBUOYANCY: force of liquid

pushing an object up

Bony Fish Anatomy…

2. Scales & Fins Outside covered with layer of smooth scales Overlap each other Scales covered with thin layer of mucus

Scales and mucus are adaptations that help fish move through water

Fins are adapted for swimming and guiding the fish

Scales

Scales and mucus are adaptations that

help fish move through water

Gills & Lungs

Bony fish DON’T need to swim to move water over gills (cartilaginous fish DO)

Have ability to pump water through mouth into the gill chamber

MOST bony fish depend only on gills, some on both gills and lungs› These fish must swim to surface of water

for oxygen

Gills & Lungs

The African Lungfish has both gills and lungs