How do fish get oxygen from under water?

Fish extract oxygen from water using specialized respiratory organs called gills. Gills are composed of thin, delicate filaments that are highly vascularized, allowing for efficient oxygen exchange. Here's a step-by-step explanation of how fish breathe underwater using their gills:

1. Water Intake: Fish take in water through their mouths or spiracles, which are small openings located behind the eyes in some species.

2. Passage Through the Gills: The water containing dissolved oxygen passes over the gills, specifically the gill filaments, which have a large surface area.

3. Oxygen Absorption: The gill filaments are lined with capillaries, which are tiny blood vessels. Oxygen from the water diffuses across the thin capillary walls and into the bloodstream of the fish.

4. Carbon Dioxide Release: At the same time, carbon dioxide, a waste product of cellular respiration, diffuses out of the bloodstream into the water through the gill filaments.

5. Water Expulsion: The water, now depleted in oxygen and enriched with carbon dioxide, is expelled from the fish's body through the gill slits or operculum (a flap that covers the gills).

6. Continuous Flow: Fish maintain a continuous flow of water over their gills by constantly moving their mouths and opercula, ensuring a fresh supply of oxygen-rich water.

It's important to note that some fish species have additional adaptations to help them extract oxygen from environments with low oxygen levels. For example, certain bottom-dwelling fish may have accessory respiratory organs, such as suprabranchial chambers, that allow them to breathe air directly from the surface.

The efficient design of gills enables fish to extract oxygen effectively from water and carry out cellular respiration, allowing them to thrive in diverse underwater habitats.