Small, freshwater fish, such as goldfish or betta fish, are ideal for living in a fishbowl. Fish tanks are required for larger fish or saltwater fish.
It's important to keep the size of the fish in mind when looking to fill a fishbowl. Certain types of goldfish and betta fish typically don't grow to be much larger than 3 to 4 inches, which means that an average fishbowl can hold two fish at a time at most. Avoid using novelty or ornamental fishbowls for keeping fish, as they often are too small for even a single fish or contain harmful chemicals.
When keeping fish in a fishbowl, there are some basic steps required to ensure the overall health and cleanliness of the fish. The most important task is regularly changing the water in the fishbowl. Once or twice a week, pour out roughly one quarter to one half of the water in the fishbowl and refill it with bottled drinking water. Tap water contains minerals and chemicals that, when left untreated, make freshwater fish ill. Remember to leave a few inches of space at the top of the bowl to avoid any unnecessary spills.
Both goldfish and betta fish can be kept in fish tanks, if so desired. Fish tanks often come with their own filtration systems and are easier to maintain overtime.