Redtail Filefish
The redtail (black-headed) filefish is a small, commonly imported Pervagor that stays modest in aquaria — roughly 9-10 cm, well under the ~16 cm wild maximum FishBase reports. It has a hobby reputation as an 'Aiptasia eater', but the fish actually sold and documented for that job under that name is a different species, Acreichthys tomentosus; reports of P. melanocephalus reliably clearing Aiptasia are anecdotal, inconsistent, and likely conflated with that other species — don't buy it specifically for pest control. Like other filefish it is not reef-safe: it will pick at ornamental invertebrates and nip coral polyps, so keep it fish-only or with only the hardiest, least valuable corals.
Tankmates
How Redtail Filefish gets on with the rest of the reef, checked pair by pair by the same engine as the live pre-flight.
Best kept apart
A real clash — aggression, predation or a same-genus fight.
Keep an eye on these
Usually fine, but worth watching in a smaller tank.
Good tankmates
No conflicts — a few popular ones to start with.
