1. The Fish Body
Section 33.1

2. Modern Fish Key Characteristics:
Gills – function to remove oxygen from water; have a large surface area and rich supply of blood
Single-loop blood circulation – blood moves from heart  gills  body  heart
Vertebral column – internal skeleton made of either cartilage or bone

3. Gills

4. Gills
Made of gill filaments – projections which increase the surface area and are rich in blood
Water is drawn into the mouth and then forced over the gills and out the gill slits
Water flows in one direction and the blood flows in the opposite direction – countercurrent
This means that diffusion happens all along the gill length

5. Flow through the gills

6. Circulation Chamber-pump heart with four chambers in a row:
Sinus venosus – collection chamber
Atrium – thin, muscular walls to hold blood
Ventricle – thick-walled, muscular chamber to contract and push blood to gills and the rest of the body
Conus arteriosus – a second pump to add more force

7. Circulation of blood

8. Kidneys Salt water fish lose water from their bodies
Freshwater fish gain water
Kidneys help maintain proper water concentration
Contain nephrons – tubes that regulate salt and water content and remove wastes from the blood
Kidneys produce urine – salt water fish excrete small amounts; freshwater fish large amounts

9. Internal anatomy

10. Reproduction Sexes are separate
Fertilization occurs externally – spawning
Eggs and sperm are released near each other in the water
Eggs contain a yolk sac with nutrients for the developing young
Some species of sharks have internal fertilization of the eggs within the female’s body

11. Fish embryo with yolk sac

12. Shark Egg