Question: how big do rainbow fish grow?
Answer: Most species of rainbowfish are less than 12 cm (4.7 in) in length, with some species measuring less than 6 cm (2.4 in), while one species, Melanotaenia vanheurni, reaches lengths of up to 20 cm (7.9 in). They live in a wide range of freshwater habitats, including rivers, lakes, and swamps.