- The fish's mouth and gills work together to take in oxygen and expel carbon dioxide.
- When the fish opens its mouth, water enters through the mouth and passes over the gills.
- The gills are lined with tiny blood vessels that absorb oxygen from the water and expel carbon dioxide.
Circulatory System and Respiratory System
- The gills also serve to transport blood from the heart to the rest of the body.
- The blood vessels that line the gills absorb oxygen from the water and carry it to the heart, which then pumps it to the rest of the body.
Excretory System and Circulatory System
- The kidneys filter waste products from the blood and produce urine.
- The urine is then transported to the bladder and expelled from the body.
Nervous System and All Body Systems
- The nervous system controls all the other body systems.
- The brain sends messages to the muscles to move, to the heart to beat, and to the gills to breathe.