Peacock gudgeons and betta fish are excellent tank mates as they prefer the same water conditions. Betta fish stick to the middle and upper area of the tank while peacock gudgeons are bottom dwellers. Betta fish do vary in temperament, however. If you have a very aggressive betta, make sure the aquarium is at least 20 gallons in volume. That way the peacock gudgeon won't be chased too often.