Many plants will thrive in water, including dwarf peace lily (Spathiphyllum), Chinese evergreen (Aglaonema), and pothos (Epipremnum). All grow roots apart from any contact with soil in typical indoor light conditions. Remember that you need to feed your beta fish brine shrimp, water fleas, bloodworms, or other similar creatures in order for it to survive. Contrary to urban legend, beta fish is a carnivore and will not feed on plant roots. If you observe your fish nibbling at the plant roots, it's most likely that it is eating bacteria on the roots and not the roots themselves.