Fish call each other to maintain group: New Zealand research

New Zealand scientists said Wednesday they had proof that fish called to each other to maintain contact -- in the same way some mammals do.

The findings meant that fish were now the oldest vertebrate group in which such behavior had been observed and furthered understanding of evolutionary behavior among vertebrates, said researcher Lucy van Oosterom, of the University of Auckland.

While it was known that fish sent messages to each other for mating or defense purposes, it was the first direct evidence that fish communicated to keep together as a group in the same way as chimpanzees or elephants.

The research team studied captive wild bigeyes (Pempheris adspersa), a species commonly found along New Zealand's northeast coast, van Oosterom said in a statement.

Bigeyes were generally nocturnal, retreating to caves during the day and foraging at night in loosely-knit shoals, and were known to have a distinctive "pop" call with an estimated maximum range of 31.6 m.

In experiments carried out over five months, the researchers played two types of sound to the captive fish: one of their normal reef environment; and another recording of bigeye vocalizations.

When the sound recordings were played, the bigeyes swam closer together and increased their own calling rates by more than five times in order to maintain contact over and above the background noise.

When there was no sound, the fish swam further apart.