I have never seen a Halequin Bass longer than about 5 inches, and I have seen many dozens over a lot of years diving and collecting in the Caribbean. Most adults are about 4 inches, measuring from the nose to the base of the tail fin. There does not seem to be that much variability in size among the basslets, unlike reef fish in other families. For example, most adult Queen Angels are about 8 to 10 inches Sl, but every now and then you see a giant.
Harlequins are small but very predatory fish, and should not be kept with anything much smaller than they are. They act like little groupers, and can swallow fish and shrimp-type inverts more than half their size. Like most predators, they tend to ignore fish that are established members of the aquarium community, tending to go after newly introduced fish. Until they get really hungry.
