The turquoise waters of the coral reefs are packed with species that still harbour many secrets. This is the case of Onuxodon, small fishes that live inside the shells of pearl oysters. An unusual and discreet shelter that makes any behavioural studies rather difficult. And yet, recent research conducted at the University of Liège has established that they emit sounds from dusk till dawn. A nocturnal activity that complicates observations, but has led scientists to assume that this is a call for a mate during reproduction cycles. One convenient yet surprising particularity seems to be the role of the amplifier, played by the oyster shells.