Yeah me too.
Don't you think though if those were parasites out of the rope that it'd be in bad shape?
I was debating that in my head... then i started to think, would it be possible to keep it looking decent / healthy if it was kept in an aquarium and being very well fed???
Although, that would then make me wonder if the person who sold the fish to the OP had seen these worm like critters in his own tank too, especially if it was a kept in a bare bottom tank prior to being sold?
As for how i came to this conclusion, im pretty much basing it solely from having kept puffers who’ve had parasites in the past... when i first got them they would look (more or less) totally healthy until getting them home and slowly seeing signs of parasites in their poo...
And to be fair, parasites can quite crafty in the sense they can reproduce like crazy before actually showing an real signs of them actually having infected a fish, which may or may not be the case here???
Guess we really need a bit more info from the OP before we can decide what they might be???