Two weeks ago, I added a harlequin tuskfish to my 90-gallon reef tank with the understanding that it’s a peaceful fish. Then this morning, the stupid thing ate my skunk cleaner shrimp right in front of me! Was I misinformed about this fish’s temperament? Eating tankmates whole seems like pretty aggressive behavior to me. Also, I was under the impression that predatory fish usually leave cleaner shrimp alone because they recognize that they’re helpful. Is that not the case?” – Submitted by Jen
I don’t know that I’d say you’ve been misinformed about this species’ temperament exactly, but it may be that you’ve misinterpreted or misapplied a few terms here.
First, the term “peaceful,” as applied to the harlequin tuskfish (Choerodon fasciatus), is very much a relative one. Perhaps a better way to describe this species’ temperament is that it’s not overly aggressive as wrasses go. I would actually describe this species as peaceful to semi-aggressive, with specimens tending to increase in aggressiveness as they mature.
The second point I’d make is that predation and aggression aren’t necessarily interchangeable terms. Some fish can be highly predatory yet coexist quite peacefully with a broad range of other fish in captivity—as long as their tankmates don’t include their natural prey items or similar species, that is. For example, my blue-throat triggers are completely inoffensive toward all their piscine tankmates, yet they’ll gobble up any zooplankton that should happen to drift through the water column with gusto.
On the other hand, some fish that aren’t especially predatory at all can be explosively aggressive toward tankmates of all shapes and sizes in defense of claimed territory. The various Stegastes spp. damsels (the “Gregories”), which feed predominantly on algae as adults, come to mind here.
With respect to your question about predatory fish leaving cleaner shrimp alone because they recognize they’re beneficial, you have to keep in mind that the “truce” that exists between marine predators and cleaner organisms is always tenuous at best. When circumstances are right—for example when the cleaner and predator are kept together permanently in a closed aquarium system—there’s always a possibility that the predator’s instinct to take advantage of an easy meal will override its forbearance at some point, thus turning the helpful cleaner into a tasty appetizer.
Also, don’t forget that crustaceans are a mainstay in the harlequin tuskfish’s natural diet, so it’s not entirely surprising that it ultimately gave in to temptation.