Goldfish are part of the stenohaline species of fish and tolerate only fresh water, according to Live Science. Both wild and pet goldfish thrive in cooler water temperatures. Ideally, water temperatures should stay between 64 and 72 F.
Wild goldfish prefer freshwater habitats that feature muddy water such as stagnant ponds or pools with little or no current. Pet goldfish require aquariums with at least 10 gallons of water and a filter to help reduce waste build up. The Washington Post recommends replacing 25 percent of the tank water every four to five days and doing a full water replacement once a week.