the mantis is a smasher and so far it's been a month and i've seen no casualties, the mantis is still settling in(found his burrow, only have seen him once) so it may change once he becomes more active but even when the YTBD came up to check him out and almost started to harrass him the mantis ignored it. if you get the right mantis then they can be quite fish safe, common sense is also needed. you don't want to get a wrasse that's going to be sticking it's face down into the mantis shrimp's den or a small goby that is going to perch motionless a few inches away from the mantis and then not keep the mantis well fed. for me the reason why i don't have a black cap gramma is because i haven't seen any for sale and partially because i want to get a bit more rock before getting one so that it can have plenty of caves, i'm also at the point where i believe i've almost reached my stocking limits, i may acclimate the molly back into FW and get rid of it if i see a black cap gramma.