Underwater GoPro footage has helped provide Kiwi scientists with the first direct evidence that groups of fish communicate to keep safe from predators.
While scientists have known fish send messages to each other for mating purposes or to defend territory, this is the first time research has shown they also use special "contact calls" to keep together.
The team from the University of Auckland's Institute of Marine Science published their findings overnight in the international journal Nature Scientific Reports.
Led by Master's degree student Lucy van Oosterom, the researchers carried out experiments using captive wild bigeyes, a nocturnal, cave-dwelling species found along New Zealand's north-east coast. Bigeyes have a distinctive "pop" call, which has an estimated range of 31.6m. This vocal behaviour, coupled with relatively sensitive hearing organs, led researchers to assume bigeyes communicated in groups - but evidence has been anecdotal, until now.
Using underwater hydrophones, a GoPro camera and an MP3 player, the team played recordings to the fish of their reef environment and another of bigeye vocalisations.
When played, the bigeyes increased their calling rates more than five times to maintain contact over the background noise. They also swam closer together. When there was no sound, the fish swam further apart.
"This study means that fish are now the oldest vertebrate group in which this behaviour has been observed and that has interesting implications for our understanding of evolutionary behaviour among vertebrates," Ms van Oosterom said.
• University of Auckland scientists have proved fish communicate to keep safe from predators in the same way animals such as chimpanzees and elephants do.
• The research is the first direct evidence that fish communicate to maintain group cohesion.
• It means fish are the oldest vertebrate group in which this behaviour has been observed, raising implications for our understanding of evolutionary behaviour among vertebrates.