A closer look at the habits of Wakatobi’s bumphead parrotfish

The reefs of Wakatobi are known for an abundance and diversity of marine life —much of which falls into the category of small to mid-sized creatures. But it’s not all about the little guys. Among the heavyweights you may encounter along the reefs are rays, turtles, the occasional shark and the world’s largest parrotfish.

Though called by different names — bumphead parrotfish, humphead parrotfish, double-headed parrotfish, buffalo parrotfish, and giant parrotfish — there’s no confusing an adult Bolbometopon muricatum for any of its parrotfish relatives. These fish can weigh in at up to 75 kilos / 165 pounds, and grow to lengths of 1.5 meters / 5 feet. From a distance, the only animal you might mistake it for is the humphead wrasse, as both sport a similar knot-like projection on their foreheads. But these outsized wrasses are rare in Wakatobi waters, while running into a bumphead parrotfish is a fairly common occurrence on certain Wakatobi dive sites. And more than likely, when you see one, more will be nearby.

Around the world, the greatest threat to bumphead parrotfish is from humans, but that’s not an issue within the protected waters of Wakatobi. Photo by Walt Stearns

Social creatures

Bumpheads are gregarious creatures. During daylight hours they can be found resting in small shoals or moving along the reefs in loose formation. Once they start grazing on corals a group of bumpheads may spread out like a herd at pasture, but come evening, they will generally regroup in a sheltering area of the reef or a protected inshore cove. These fish aren’t known for blowing protective bubble cocoons like some smaller species of parrotfish, as their only natural predator is large sharks, which are infrequent visitors to the reefs of Wakatobi. Around the world, the greatest threat to their safety is from humans, as netters and spearfishermen have learned to exploit these fishes’ social tendencies. Fortunately, that’s not an issue within the protected waters of the Wakatobi Reserve.

Bumpheads graze calmly, like every other member of the parrotfish family, using their powerful jaws and hardened teeth to turn reef into sand. Photo by Walt Stearns

About that bump

The distinctive forehead growth that earns the bumphead its common name is a feature that these fish grow into. Juveniles of the species are bump free, and sport vertical rows of small, whitish spots. As they mature, they develop a more uniform olive to slate grey coloration and start to develop their distinctive forehead humps. The value of these protrusions have become the subject of some interesting theories. One explanation that gets a lot of traction on the Internet is that this protrusion is a biological battering ram that these coral-grazing fish use to demolish tasty portions of the reef for easier consumption. While interesting, there are several reasons why this explanation should likely be put in the myth category. First, there’s nothing other than third-hand anecdotes that support this supposition. The photo and video records show these fish grazing calmly like every the member of the parrotfish family, using their powerful jaws and hardened teeth to turn reef into sand. And then there’s the physiological question. These protrusions are not made of hardened bone, but of a softer tissue that would likely be injured by repeated headbutting against the reef.

Bumphead parrotfish start life as females, then transition to males as they become a large, dominant fish in the group. Photo by Walt Stearns

Gender benders

So with the myth of the battering ram likely busted, what’s the point of the bump? Like so many things on both land and sea, it may be a sex thing. As members of the parrotfish family, bumpheads are hermaphroditic. They start life as females, then transitioning to males as they become a large, dominant fish in the group. Bumphead schools may contain a single male, or several large males, along with several large terminal females. If males are removed from the equation for any reason, a terminal female can transition to the male role in a matter of days.

Just showing off?

With an understanding of parrotfish gender fluidity, let’s return to the question of the bump. More than likely, the bump is a statement of age-related status and masculinity, a biological ornamentation in the same vein as a peacock’s plumage or a lion’s mane. Yes, it begins to appear as females reach sexual maturity, but it doesn’t become prominent until they reach the terminal stage. By then, they may be called on to switch gender roles in short order, and as with any male creature that sports horns, teeth or imported sports cars, there may be competition for the top spot.

More than likely, the bump is a statement of age-related status and masculinity, a biological ornamentation in the same vein as a peacock’s plumage or a lion’s mane.

Male rivalry displays in bumpheads is not a well-observed phenomenon, but it has been described by some researchers, including a group studying these fish in the Pacific’s Wake Atoll. Reports tell of alpha males vying for status by swimming directly at each other, butting heads and then resorting to flank biting. Given the confrontational behavior of competitive males in every species from elk to elephant seals, it’s not surprising to think that bumpheads would engage in this type of behavior. It’s probably just a guy thing.

The largest and bumpiest bumpheads are almost always males. Photo by Erik Schlogl

Bumphead parrotfish are just one of the thousands of unique creatures that you will find in the waters of Wakatobi. Isn’t it time to discover or rediscover the wonders that await on the reefs of our marine preserve? Planning a visit is as easy by contacting our office at office@wakatobi.com, or completing a quick trip inquiry at wakatobi.com. A guest experience consultant will be in touch with you to answer any questions and provide more information on the Wakatobi experience.

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