Do some googling, they're not hard to sex. If I remember correctly, the males have the striped pattern on top of their nose continue down underneath their chin. In females, the stripes stop half way down
I’ve done research n I m almost positive I have female just wanted confirmation of it from someone w lot experience w Valentini puffer s. Also I had store order a male for me n I also worried bout when adding him if there could be any harm or poison released from them being that they are semi aggressive n not post to have more then one in a tank unless it’s opposite sex I was still concerned cause my tank is doing well but only has my female Valentini n firefish