I feel like this is basic knowledge. There is oxygen in water which fishes need. The oxygen is recycled by coming into contact with fresh oxygen from the atmosphere. Keep a fish in a bag and it will eventually die from lack of oxygen after it's depleted the concentration of oxygen in its water..
Just some news. In a pet store we put extra oxygen in the bag before sealing it. This is special produced so it wil mix better with the water. There is a big diffrence between them.
My friend had a murderer fish, he killed everything else in the tank, including his brothers and the plant. She got so mad she flushed him down the toilet. He came back up three times until she bleached him... twice... I'm just hoping she never gets mad at me
*fish