We have read of reports indicating the tail is used as a club or a whip, but have never witnessed this behavior. The tail is dark brown with indistinct rings matching the body ground color. Unlike many monitor species, acanthurus get more beautiful and colorful with age. Acanthurus are a stocky, robustly proportioned animal whose maximum length is under two feet. Tail size is one and a half to two times the snout to vent length.
Males appear larger than females because they are much heavier and wider of body.
It surprised me to find that overall length is essentially the same. The intelligence of acanthurus monitors is evident as they inspect their environment, flicking their tongues quickly as they move about the enclosure. They dig and search for new areas to explore, thoroughly investigating anything new in their environment. Males are generally more outgoing than females and are visibly prominent in their habitat, whereas females often prefer the security of hiding places and tend to be more reclusive. Young Ackies are flighty and reclusive by calm right down with a little age and soon learn to recognize their keeper.