The same reason you run more actively with air in the atmosphere. Without air, and therefore oxygen, you and the goldfish will suffocate, making it difficult to swim or run.
You take in oxygen through your lungs; the goldfish takes in oxygen through its gills.
What else would you expect them to swim in? Of course Goldfish swim in water.
Yes, actually it must be in water. If the goldfish is not in water, it will die due to suffocation.
Freshwater
change water
A 5-gallon tank is not recommended for keeping a goldfish. Goldfish require a larger tank size to thrive, ideally 20 gallons or more for a single goldfish. A larger tank provides more space for the goldfish to swim and grow, as well as better water quality.
Yes, the bigger the tank, the bigger they will grow. Yes. The more resources given to the goldfish * more oxygenated water, * aquarium plants, * room to swim, * cleaner environments, the larger the fish will grow
Goldfish make bubbles on the surface of the water by releasing air from their swim bladders through their mouths. This process is called "gulp breathing."
No
A goldfish is not from the fish type of anabantid (labyrinth fish) who would actually really drown if they do not swim up to the water surface to breathe.
The size of a tank can affect the growth of goldfish. A larger tank provides more space for the goldfish to swim and grow, allowing them to reach their full potential size. In a smaller tank, goldfish may be stunted in growth due to limited space and water quality issues.
A damaged swim bladder.
Goldfish make bubbles because they release excess air from their swim bladders, which helps them regulate their buoyancy and stay balanced in the water.