Groups Of Fish Use Contact Calls To Stick Together, Researchers Say

Fish seem to play a Marco Polo-type game when traveling in large groups, as a means of staying close together and bettering their chances of safety, according to a new study from the University of Auckland. While previous studies have shown fish send messages to each other for mating purposes or to defend territory, this is the first time researchers have proven they use contact calls to maintain group cohesion.

In the latest study, researchers from the university's Institute of Marine Science investigated the contact calls used by captive wild bigeyes (Pempheris adspersa), whose shouts and hollers have a range of about 100 feet. Bigeyes are a common fish species found along the coast of New Zealand. They are primarily nocturnal fish that forage at night -- rather independently, but still in close contact -- in loosely-knit groups.

Researchers played two kinds of sound recordings for the fish through underwater hydrophones: The first was of the normal ambient sounds of the reef tank where the fish were kept, while the second was of previously recorded bigeye vocalizations, according to a news release.

Overall, researchers found the fish grew five times more communicative with their calling rates, "talking" over the background sounds to stay in touch and swimming close together, when the recordings were played. However, when no sound recordings were played, the bigeyes swam farther apart.

"This study means that fish are now the oldest vertebrate group in which this behavior has been observed," Master's student Lucy van Oosterom, lead researcher on the study, said in a statement. "And that has interesting implications for our understanding of evolutionary behavior among vertebrates."

Their study was recently published in the journal Scientific Reports.

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