Not unusual. Many of the online vendors don't even give you the option to buy females versus males. You don't say how large they are. That can go a long way to determining success (generally, smaller is better; though not too small). Also depends a bit on whether they are sub-males or not. I've got 10 in my tank, and probably 7 are males, but its a 450 with lots of flow and I feed them a ton. Also keep in mind that you will almost certainly lose some of them to shipping/acclimation stress. Agree with TJ that Bartlett are more 'chippy' than homicidal.