Two of the most common crustacean zooplankton <i>Meganyctiphanes norvegica</i> and <i>Calanus</i> spp. produce sounds within the hearing range of their fish predators

Sound is an effective channel for the transfer of information underwater. While it known that fish and whales can use sound communication, as a cue to localise predators prey, much less about production in invertebrates. Here we describe sounds produced by two most common marine crustacean zooplankton Northern hemisphere: krill (Meganyctiphanes norvegica) copepods (Calanus spp.). The recorded were taxon-specific within hearing range planktivorous fish. We similar laboratory field. In krill, co-occurred with tail flip, amplitude was correlated displacement distance animal, indicating potential producing mechanism. Our findings highlight possibility could be used their intraspecific communication.