In the freshwaters of much of sub-Saharan Africa, a few fishes share an extremely rare practice: they chomp on and eat the fins of their neighbors.
To better understand this bizarre behavior, for which the new term “pterygophagy” has been coined, Museum ichthyologists used DNA barcoding to investigate the fin-eating fishes’ preferred prey. Their research has revealed that these fishes will target just about any species—including their own.
“The jaws of these fishes are highly specialized for fin-eating, which is a very uncommon behavior,” said Melanie Stiassny, Axelrod Research Curator in the Museum’s Department of Ichthyology. “Although when young, some of these fishes will eat smaller fish whole, by the time they are adults most of them only care about biting off those fins.”
The new work, recently published in the journal Ecology and Evolution, focuses on three of the four lineages of ptergygophages in the family Distichodontidae, which were first documented 50 years ago. Previous work has led to two hypotheses about fin-eating behavior in these fishes: that they target specific prey and that they use “aggressive mimicry” to blend in with their prey and, as a result, become more effective hunters.
To investigate these ideas, Dr. Stiassny and Jairo Arroyave, an Axelrod Postdoctoral Fellow at the Museum, set up a mentoring project for a team of New York City high school students participating in the Urban Barcode Research Program of Cold Spring Harbor Laboratory’s DNA Learning Center.
The research team used DNA barcoding to identify prey species from fin fragments found in the stomachs of distichodontids collected in the Congo by Stiassny and colleagues. DNA barcoding uses a relatively short gene region in the mitochondrion—an energy-generating structure in the cells of all multicellular animals—to identify the species the material is from.
“Depending on the state of digestion, it’s often extremely difficult, if not impossible, to identify what kind of food is in the stomach of a fish by visual inspection alone,” Dr. Arroyave said. “But DNA barcoding lets us identify the animal a small piece of fin came from quickly and accurately.”
The results negate both of the previous assumptions about pterygophagous distichodontids. Researchers found fin fragments from a wide array of species in the sampled stomachs, indicating that the hunting fish are not at all picky in prey selection. The team also found evidence of cannibalism in at least two of the species studied—the first report of fish eating parts of their own kind. Although cannibalism in fishes is not uncommon, virtually all previously known instances involve adults eating their own offspring.
In addition, no links were found between the appearance of the fin-eating fish and their prey, suggesting that they do not use mimicry as a hunting strategy.
“We had assumed that because these fishes are so specialized in behavior and morphology, they would be constrained in what kind of prey they could target for fins,” Stiassny said. “So we were surprised to find that it’s quite the reverse. They turn out to be ‘specialized generalists,’ able to snatch the fins from just about any species of fish they come across—and are probably very resilient to environmental change as a result.”