Fishes have gills that extract oxygen from water. Water passes over the gills as fish swim, allowing oxygen to diffuse into blood vessels and carbon dioxide to diffuse out. There are three main classes of fish: jawless fish like lampreys and hagfish that lack jaws; cartilaginous fish like sharks that have skeletons made of cartilage; and bony fish, which is the largest class and have skeletons made of bone. Bony fish use a swim bladder to control their buoyancy and have scales and fins adapted for swimming.

1. 17.2 FISHES Page 348

2. Gills Organs that remove dissolved oxygen from water Located on either side of fish’s head

3. Gills

4. 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

5. 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

6. 3 Classes of Fish Jawless Fish {Agnatha} Cartilaginous Fish {Chondrichthyes} Bony Fish {Osteichthyes}

7. 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

8. Jawless Fish LAMPREY HAGFISH

9. 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)

10. 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

11. Cartilaginous Fish Examples SHARK STINGRAY WHALE SHARK

12. Bony Fish Greatest number of fish belong to this class Have skeletons made of bone

13. Bony Fish Examples CATFISH SALMON GOLDFISH

14. Bony Fish Anatomy 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

15. Bony Fish Anatomy

16. 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 stayat any level (FISH)

17. Buoyancy Illustrated BUOYANCY: force of liquid pushing an object up

18. Bony Fish Anatomy… 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

19. Scales Scales and mucus are adaptationsthat help fish move through water

20. 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

21. Gills & Lungs The African Lungfish has both gills and lungs