https://www.youtube.com/watch?v=Av06V-ZWbJ8

Some super cool facts about Harlequin Filefish:

• They smell like Acropora … literally.  Researchers discovered that these filefish end up smelling like what they eat in order to camouflage themselves from predators.
• Harlequin Filefish are real masters of disguise.  Aside from their olfactory slight of hand, they also possess incredible visual camouflage. Their orange polka-dots mirror the corallites of Acopora, and their white, tapered tails even mirror the tips of staghorn coral.  See the photo on the right.
• Their first dorsal fin is a hard, sharp barb.  What’s it used for?  To anchor itself on Acropora while it rests … in a position that makes it look like just another branch on the coral.
• Filefish form monogamous pairs for life.  The video says it all.  There’s something very romantic about two gentle seafarers spending their entire lives drifting together in a tropical paradise.
• These fish have a strong dietary preference for corals, especially Acropora millepora.  The preference is so strong that it borders on monophagy (acceptance of only one type of food).  Harlequin filefish have been observed to starve to death when their preferred foods suddenly become unavailable (e.g. bleaching) even though other food sources are present.

As you can see above, these guys are also darlings of the research community.

Note: While gorgeous and all-around awesome, Oxymonacanthus longirostris require special care and should be left for advanced fishkeepers.  They have been weaned onto prepared foods in captivity, but the acclimation process is not for the novice.