1. Respiratory System: Purpose: - exchange O 2 and CO 2 between an organism and its environment -fish use their mouths to breath and not nostrils.

2. Respiration: Gills have a large surface area which allow for rapid exchange of oxygen and carbon dioxide -Occurs in a fish’s gills -gills are located on the sides of a fish’s head

3. Each gill is composed of 4 gill arches -a gill arch is a curved, cartilaginous bone -on the outside of each arch is a double row of thin projections called gill filaments.

4. Gill filaments are feathery structures which increase the surface area of the gill for gas exchange. Each filament contains many blood vessels

5. Gill arches also have gill rakers -located on the inside of the gill arch. -rakes out or filters out food, preventing food from entering the gills.

7. Water enters the mouth and is pumped over the gills. Water flows over the filaments which are loaded with blood vessels. The dissolved oxygen from the water diffuses into the blood. Blood transports oxygen to the cells.

8. Cells take in oxygen and release carbon dioxide as a waste. Carbon dioxide enters blood and is transported back to the gills where it is released into the water The operculum covers the gills.

10. Excretory System: Purpose: to remove nitrogenous waste (ammonia) from the blood which is created by the cells going through metabolism Kidney Urogenital opening

11. 1. Blood containing ammonia can pass through the gills and be excreted out into the water. OR 2. A fish’s kidney can filter out the ammonia and convert it into a less toxic urea along with excess water and salt.

12. Urea, excess water and salt collect and stored in the urinary bladder as urine. Urine is then released out the body through the urogenital opening. Urinary bladder

13. Water moves from high to low. A large amount of water moves into the fresh water fish from its environment. Therefore they excrete large amounts of urine constantly. Only a small amount of water moves into the salt water fish from its environment. Therefore they excrete very small amounts of urine. High Low