Surgeonfish's revenge

Courtesy of Kendall Clements

Surgeonfish aren't as dedicated to life-saving as their name implies - quite the opposite, in fact. While sample-gathering in the Seychelles in May 2001, marine biologist J. Howard Choat wrongly assumed that he had killed a surgeonfish (genus Naso). When he took the fish off the spear, one of its razor-sharp caudal knives sliced open his right palm, severing two tendons. He received timely emergency care, but the wound didn't heal properly, leaving him with an uncontrollably stiffened outstretched middle finger. This was socially awkward, to say the least, so Choat asked a "real" surgeon to sever the tendons, and now his middle finger hangs limp. He calls this "the surgeonfish's revenge."

When Kendall Clements, a marine biologist at the University of Auckland, snorkels from his boat to an idyllic tropical reef to gather samples of surgeonfish for his nutritional ecology studies, he brings a spear gun and dons a full-body Lycra suit to save his skin from jellyfish stings. Caution instructs him to not put too many fish in his mesh bag or stray too far from the boat, for on the way back he might have to fight off reef sharks with ambitions to turn his quarry into a delectable amuse-bouche. It "helps to have a colleague along" to snag an impaled fish before a shark may get to it, he notes. He also has to be a crack shot, for if he spears a fish through its intestines and spills out their contents, he loses valuable data.

Surgeonfish are so named because of the efficient slicing ability of the caudal knives which can project more than an inch from the sides of their tails. They have "leathery hides, venomous dorsal and anal fins, tough spines," and "very few predators," notes Choat. These protective adaptations, however, promote complacency in the presence of larger animals, which makes surgeonfish relatively easy to spear.

Clements has collaborated and shared specimens with Choat, professor emeritus at James Cook University of North Queensland, Australia, and with Esther Angert, a microbiologist at Cornell University. As part of his work, Choat establishes the ages of the surgeonfish. First, he measures the size of mineral deposits called otoliths in their ears. Next, he thin-sections the otoliths and examines their internal structures to provide confirmation of age, much like counting tree rings. Finally, he correlates age with fish size to spare future fish the spear for age-determining purposes.

By tracking surgeonfish, the scientists also track coral reefs, since surgeonfish maintain the reefs' health. Some species are herbivores, grooming the coral as they graze on algae. Others eat plankton, or are detritovores, preventing wastes and other residues from accumulating in the reefs. Clements has associated nutrient assimilation and gut flora with diet, and learned that surgeonfish share traits with terrestrial animals. For example, the herbivores, like cows and other terrestrial ruminants, rely on fermentation by a complex community of symbionts, whereas other types of surgeonfish that eat a range of foods have a simpler internal flora.

Despite the dangers, working with surgeonfish has its perks. Angert studies members of the genus Epulopiscium, one of the largest known bacteria (even visible to the naked eye), which dwell in the surgeonfish gut. Their physiology is poorly understood, and they have yet to be cultured in vitro, leaving a "24-hour window to get as much work done as is possible before the bacteria die," according to Angert. As a result, she works in labs located near tropical reefs. An optimal site is at the Lizard Island Research Station on the Great Barrier Reef, which shares the island (but little else) with an ultraexclusive resort.

Her need to work practically in situ means that she must get funding to travel to many idyllic sites, inspiring location envy among other scientists. For example, a negative review of a grant proposal gratuitously mentioned: "On the minus side, this bacterium cannot yet be grown in culture.... Apparently surgeonfish cannot be raised in Ithaca, so the study of live cells is limited to the periods when the PI and/or lab members are able to travel to Hawaii and Australia (perhaps this last point should be added to the plus side)."