Depends on the Betta, set up and the size of the shrimp. My first Betta gorged himself on my smaller shrimp and that may well have contributed to his death (though I still think there was something internal going on), second Betta who is thriving will harass them a bit but he hasn't had much of an impact on them but that could be because a lot of the shrimp that were left are the larger ones so too big for him to eat. I also have plenty of places for them to hide so I'm still getting a lot of babies.