Puffers and Bettas

I wouldn't suggest it at all...Ive seen DPs go after fish with pretty much no color/fins let alone something with the size/color of a Female Betta. IMO you should keep DPs in a DP tank...if heavily planted and VERY well established as a group, size of group depending on size of tank, MAYBE some Otos, or some cleaner shrimp if you dont mind them getting eaten!
 
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