I was thinking the same, but looking at the feces, I'm not so sure (she's eating garlic+brine shrimps).
The black part was harder than the rest. What do you think?
I have a female Betta Splenders, she has bright colors, no issues swimming but she has a really bad growth on a side of the belly.
We quarantened her in a 5L tank to check how her feces were and to make her and other fishes safe.
At the beginning she had stringy poop and we (my bf and I) thought...