How long a fish can live out of water depends on the species of fish, as some fish can survive for up to a few days while others can only survive for minutes. The fish that can survive for a few days without water do so by breathing the air or by absorbing it through skin.
Fish are able to swim and breathe underwater thanks to their intricate gill system. The gills have filters that remove the oxygen from the water that enters and then process the oxygen for use in the fish's system. Scientists believe that fish were found on the Earth approximately 1.7 million years ago and evolved from another species.
It is recommended that an owner of a pet fish not take their fish out of water ever unless transferring between two water areas because pet fish have a tendency to die quickly when left out of water. It is also inhumane to kill a fish by leaving it out of water to suffocate. Most scientists and veterinarians agree that a fish is dead after 10 minutes without gill movement.
Fish can swim for long periods of time, but whenever they get tired they will let themselves flow freely on a current in the water. This helps them avoid using too much energy and oxygen.