The Green Tiger Barb is the same species aas the regular TB, Barbus tetrazona, so theoretically could grow to the same size. These tend to max out at about 75-80mm say 3 inches. In practice most TB's never reach this size. The green variety is man made and somewhat inbred, so rarely gets to the same size as their normal bretheren in the same tank. They should get to 60-65mm though.