How did the fascinating behavior of archerfish evolve?

Archerfish – a small group of fishes that live in Southeast Asia, Australia, and many regions in between – are famous for their amazing ability to shoot down land-based insects with highly accurate streams of water that they project from their mouths. Until recently though, not much has been known about these peculiar aquatic creatures. 

Questions regarding the number of archerfish species, how they are related to one another, and what is their evolutionary history have remained shrouded in mystery. However, a recent study led by the University of Kansas (KU) Biodiversity Institute & Natural History Museum has now provided the most thorough examination of the evolutionary history and anatomical variation of archerfishes.

“There are other fish that eat insects and some that will jump out of water, but I would say there’s nothing really like this,” said study co-author Dr. Leo Smith, an evolutionary biologist and associate curator at KU’s Biodiversity Institute & Natural History Museum. “There’s a potentially apocryphal story, which is that back in the mid-1800s in India, archerfishes would shoot out the colonizers’ cigarettes, just like if there was like a lightning bug. They would shoot them out and drive people crazy.”

In order to understand how this amazing behavior evolved, the researchers collected tissue samples and specimens of archerfish from various institutions and museums around the world, and analyzed their structures and genetic features. Their analyses revealed that, although the oral structures of archerfishes support a blowpipe mechanism that is common in many fish species, several unique soft-tissue oral structures may also play a fundamental role in shooting, distinguishing them from related types of fishes.

“Just because other fish can move water, it’s not anything like this,” Dr. Smith explained. “I equate it to, ‘I could put a trumpet in my mouth, and I suppose I could make noise come out of it, but not like Miles Davis.’ It’s like a fundamentally different thing, too, a really remarkable specialization for catching insects.”  

According to Dr. Smith and his colleagues, archerfishes have a closely related “sister group” of fishes – the beach salmon – which have similar oral structures used to shoot water towards prey, suggesting that this capacity could be what evolutionary biologists call a co-opted or exapted trait.

“We think of adaptations like, for example, a sailfish that has this really beautiful sail on their dorsal fin – but a lot of fishes have dorsal fins and what they’ve done is kind of modify that dorsal fin to fit some other need,” said study lead author Matthew Girard, a postdoctoral fellow at the National Museum of Natural History.

“If we look at the group that’s most closely related to archerfish, it’s already eating hard-body things. So, archerfish must have had all the structures that would allow that to happen, and all they had to do was kind of modify those to be able to shoot. So that’s what that co-option is – it’s really a nuance saying that the necessary parts were already there and all they did was modify a few things to allow this to happen.”

An in-depth description of archerfish and their evolutionary history is published in the journal Integrative Organismal Biology. 

—

By Andrei Ionescu, Earth.com Staff Writer