yup thats what happened to me lol, my female betta and the guppy were together for awhile then all of a sudden i seen the female betta dragging the guppy by its tail, it was pretty scary to look at, i thought the guppy was dead, but i moved the guppy in with my moms tank and his tail is growing back now, so if u have another tank for ur guppy, or for ur betta then i'd move one of them