A hardy fish is any fish which is easy to maintain in a home aquarium due to its ability to adapt to a wide range of water parameters. ^[1] Such fish are good starter fish can be used for 'cycling' an aquarium (i.e. reducing ammonia and nitrites to effectively zero.)^{[2][more detail needed]}

Examples of hardy freshwater fish include Poecilids such as the guppy,^[1] molly, swordtail and platy, most species of betta, zebra danios, and some tetras. Generally, fish are hardy only when they have been tank-bred, since wild-caught fish may take many generations to adapt to life in captivity. ^{[citation needed]}