Chapter 33

Fishes and Amphibians

Section 1: The Fish Body

Section 2: Today’s Fishes

Section 3: Amphibians

Section 1

The Fish BodyObjectives:•Describe the characteristics of modern fishes.•Summarize how fish obtain oxygen.•Summarize how blood circulates through a fish.•Contrast how marine and freshwater fishes balance their salt and water content.•Describe two methods of reproduction in fishes.

Section 1

The Fish BodyKey Characteristics of Modern Fishes•Features All fishes have gills and a backbone, and they circulate oxygen-rich blood from their gills directly to body tissues.

Section 1

The Fish BodyGills•Countercurrent Flow Countercurrent flow maximizes the amount of oxygen that can be extracted from water through the gills.

Section 1

The Fish BodyCirculation of Blood•Circulation The four-chambered heart collects oxygen-poor blood from the body and pumps it through the gills where it receives oxygen. Oxygen-rich blood then circulates to the rest of the body.

Section 1

The Fish BodyKidneys•Salt and Water Balance Fish rely on their gills and a pair of kidneys to regulate its salt and water balance.

Section 1

The Fish BodyReproduction•Reproduction Most fishes fertilize their eggs externally as males and females release their gametes near one another in the water.

Section 2

Today’s FishesObjectives:•Distinguish between the three general categories of modern fishes.•Describe the major external and internal characteristics of the yellow perch.•Summarize features of bony fishes.

Section 2

Today’s FishesJawless Fishes•Hagfishes and Lampreys Hagfishes and lampreys are the only surviving jawless fishes.

Section 2

Today’s FishesCartilaginous Fishes•Sharks Sharks have light, highly streamlined bodies well suited for rapid swimming, which makes them swift and efficient predators.

Section 2

Today’s FishesBony Fishes•Features Bony fishes have an internal skeleton made completely of bone, a swim bladder, a lateral limb sensory system, and a set of gill covers called opercula.•Ray-Finned Bony Fishes Ray-finned bony fishes comprise the vast majority of living fishes.•Lobe-Finned Bony Fishes Only seven species of lobe-finned fishes survive today.

Section 3

AmphibiansObjectives:•Summarize the characteristics of modern amphibians.•Compare the three orders of living amphibians.•Describe the major external and internal characteristics of the leopard frog.

Section 3

AmphibiansKey Characteristics of Modern Amphibians•Features Most amphibians have legs, breathe with lungs and through their skin, and have two circulatory loops.•Lungs An amphibian lung is basically an air sac with a large surface area for gas exchange.•Double-Loop Circulation The amphibian heart pumps oxygen-poor blood to the lungs and receives oxygen-rich blood from the lungs. The oxygen-rich blood is then pumped to the body.

Section 3

AmphibiansFrogs and Toads•Reproduction in Frogs Frogs release their eggs into water.

Section 3

AmphibiansSalamanders and Caecilians•Salamanders Salamanders are semiaquatic predators with tails.•Caecilians Caecilians are legless amphibians specialized for burrowing.