Marine fish breathe using gills, specialized organs that extract dissolved oxygen from water.
The Gill System: A Closer Look
Fish gills are highly efficient at absorbing oxygen from water. Here's how the process works:
- Water Intake: A fish takes in water through its mouth.
- Gills and Capillaries: The water passes over the gills, which are composed of numerous branching structures containing tiny blood vessels called capillaries.
- Oxygen Absorption: The capillaries absorb oxygen dissolved in the water. Blood flows through the capillaries in the opposite direction to the water flow (a process called countercurrent exchange), maximizing oxygen uptake.
- Carbon Dioxide Release: At the same time, carbon dioxide is released from the blood into the water.
- Water Expulsion: The water, now depleted of oxygen, exits the fish through gill slits.
Importance of Dissolved Oxygen
Marine fish rely entirely on the oxygen dissolved in the water to survive. Factors that can affect the amount of dissolved oxygen include:
- Temperature: Warmer water holds less dissolved oxygen.
- Salinity: Saltier water holds less dissolved oxygen.
- Photosynthesis: Aquatic plants and algae release oxygen during photosynthesis.
- Decomposition: Decomposition of organic matter consumes oxygen.
Adaptations for Efficient Breathing
Different marine fish species have developed various adaptations to improve their breathing efficiency, depending on their habitat and activity level. Some species may have larger gills or more efficient countercurrent exchange mechanisms.
