5-7" Japanes Koi are a colorful variation of the common carp. They can help control floating algae’s such as duckweed and water meal. Koi are not sterile like the Grass Carp (White Amur) but reproduction should be controlled in the presence of bass and bluegill. Stocking Koi and Grass Carp together will have a broader effect then stocking either fish separately.