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
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
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.
A damaged swim bladder.
because they are fish
NO. Unless there in ranch
Simply put, they will die. Goldfish are coldwater fish and if their water gets too warm, their metabolism speeds up. Their bodies then demand more oxygen for them to survive. The warmer water is, the less oxygen it can contain, so coldwater fish simple die from lack of oxygen in warm water.
Anywhere :)