Some freshwater fish in sub-Saharan Africa have evolved this nasty habit where they bite off and eat the fins of other fish. DNA barcoding now shows these things are nastier and far more indiscriminate than we thought.

This behavior is exceptionally rare, but ichthyologists have a name for it: "pterygophagy." These fish have evolved highly specialized jaws for fin-eating. When they're young, some of them eat smaller fish whole, but by the time they become adults, they really only care about chomping on fins.

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Previous work has suggested these fish target specific prey while employing "aggressive mimicry" to blend in with their victims. But a new genetic analysis shows these fish will target just about any species — including their own.

A post from the American Museum of Natural History explains:

The research team used DNA barcoding to identify prey species from fin fragments found in the stomachs of distichodontids collected in the Congo by [Melanie] 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. [Jairo] 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.

The researchers also found that these fish don't use mimicry as a hunting strategy.

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You can read the entire article here. And check out the study at Ecology and Evolution: "DNA barcoding reveals novel insights into pterygophagy and prey selection in distichodontid fishes (Characiformes: Distichodontidae)".

Image: AMNH/J. Arroyave and M. Stiassny

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