the chart says compatability, meaning if they can be in the same tank (as marked on the chart) they cannot interbreed. Taht is why cherry, yellow, blue pearl and snowball (same species, different color variations) are not recommended to be kept in the same tank. Crystals and cherries can be housed together because they cannot interbreed. I would imagine black and crystal reds could, although I am not familiar with crystal black shrimp.