Betta fish grow up to 3 inches long. Male betta fish grow slightly larger than females, but they still stay within this 3-inch limit, according to About.com.
According to About.com, betta fish originate in Asia and live in shallow ponds, such as rice paddies. Captive breeding has led to subspecies with longer fins and populations of the fish outside of their native habitats. A tank size of at least 2 gallons is required to provide the proper environment for these fish, and males need to be kept separate from one another to prevent fighting. Male betta fish are more brightly colored and have longer fins and beards than females.