Here's a step-by-step explanation of how swordtail fish breathe:
1. Swordtail fish take in water through their mouth.
2. The water passes through the gills.
3. As the water passes through the gills, the oxygen in the water is absorbed by the blood vessels in the gills.
4. The oxygen-rich blood is then pumped throughout the swordtail fish's body.
5. The carbon dioxide in the blood is released through the gills.
6. The swordtail fish then exhales the carbon dioxide-rich water out through its mouth.
This process of breathing through gills is repeated continuously by swordtail fish in order to obtain oxygen from the water and expel carbon dioxide.