Boesemani Rainbow fish These fish are very colourful and very easy to keep. They are great in any community tank. Best kept in an aquarium of at least 3 feet long and 50 gallons. A 4 foot or 6 foot tank is ideal. The fish in the photos are two years old. Adults will grow to about 3.5 inches. The fish for sale are 8 months old and 1 - 1.5 inches. Rainbow fish grow slowly and take patience and good fish keeping. They like to school to together and need to be in groups of at least 6. 6 fish for $50