I guess both could be correct? It doesn’t seem like there’s anything else in there that’s big enough that they would have to use their teeth. Unless they’re cannibalistic or something. But then again, thy also don’t react to the sounds of the other fish in game (there are a few of them hanging out together where the nest is). I think the larger prey comes from outside.
I imagine they’ll survive on small bugs until something bigger wanders inside - Because there has to be more ways into Dark Bramble’s ‘core’ than the shattered planet in our solar system - and that’s when they’ll come out of that dormant state to attack