The commission shall adopt and carry into effect plans to replenish and stock the state with game and, whenever it is in the best interest of the public to do so, to stock the streams, lakes, and ponds, whether public or private, of this state with fish. It may plan such extensions and additions to existing hatcheries and such new plants as may be necessary to supply fully the state with game and fish and cause the plans to be executed after ascertaining the cost thereof.