The model is Canthigaster valentini, a small pufferfish carrying tetrodotoxin in its tissues, which predators learn to avoid. Paraluteres prionurus has no such defence. It matches the model's white body, four dark saddles and yellow tail closely, and it swims openly in the same habitat, which is exactly the behaviour a defenceless fish of that size should not risk.
This is Batesian mimicry: a palatable species gaining protection by resembling a defended one. Field work has found the mimic to be less common than the model where the two co-occur, which is what the theory predicts, since a mimic that becomes too abundant relative to its model undermines the predator's learned avoidance.
The two can be told apart on close view. The filefish has a single elongated dorsal spine, the pufferfish has none; the filefish's dorsal and anal fins are longer and more mobile; and the pufferfish's snout is blunter. The behavioural cue is that a startled Canthigaster can inflate and the filefish cannot.