Nannatherina balstoni (Balston's pygmy perch, Balston's perchlet, or king river perchlet) is a species of temperate perch endemic to Australia, where it occurs in coastal streams, ponds, lakes, and swamps. It prefers shallow, acidic waters with patches of sedge growth. This species can reach 9 cm (3.5 in) SL, though most do not exceed 6 cm (2.4 in). It can also be found in the aquarium trade.