Silence in the bedroom

Our interlocutor has moreover demonstrated that the sounds were exactly the same, apart from their duration and frequency, which are linked to the size of the individual, be they emitted by a female⁽³⁾, a male or an immature fish. In short the sex of the fish in no way influences the acoustic signature.

But there are even more surprising findings. In a study published in 2011 in the journal BMC Evolutionary Biology⁽⁴⁾, Orphal Colleye compared the aggressive sounds in 14 clownfish species. No difference! Once again only the size of the individuals, all species included, offers a nuance (sound duration and frequency) enabling them to be distinguished according to sound production. ‘Even though certain species have different body shapes, and whilst the teeth (which come into contact with each other when the fish snaps its jaws together) are caniniform in some and incisiform in others, the acoustic signature is identical,’ points out Orphal Colleye.

In the study published in PLoS One this autumn, the researcher has not merely settled for analysing the aggressive and submissive relationships in clownfish groups; he also tried to establish if sounds were produced during reproduction. This had already been observed for other species of Pomacentridae, but it still wasn’t known if it was the same case for clownfish. Armed with his 25 images/second camera and his hydrophone, Orphal Colleye first of all observed couples over a month in the Brest aquarium (Oceanopolis), where six species of clownfish are bred. No matter the species, reproduction was never accompanied by the emission of the slightest sound.

Fearing a possible behavioural bias due to captivity, the biologist subsequently travelled to the Sesoko Station on the island of Okinawa (Japan), whose coral reefs host four clownfish species. ‘Several clownfish couples are kept in semi-captivity in aquariums with conditions similar to those of the natural environment – the same photoperiod, the same water temperature, etc.,’ he says. ‘There again, the hydrophone never captured any sound over the different cycles of reproduction I witnessed.’ The same observation: the clownfish remained ‘silent.’

Why, contrary to other species of Pomacentridae spied upon during their ‘lovemaking’, do Nemo’s congeners remain silent during these crucial moments? Doubtless because the group is totally hierarchical and only the dominant male has the possibility to fertilise the eggs deposited by the female after the games of nuptial display. In short, he ‘plays the economy card.’ ‘That is my hypothesis, in any case,’ states Orphal Colleye. ‘In clownfishes, the couple can live together for several years. And the male doesn’t really need to seduce the female.’

(3) Unlike the dominant male and immature fish, the female does not produce submissive sounds.

(4) Colleye O., Vandewalle P., Lanterbecq D., Lecchini D., Parmentier E. 2011. Interpsecific variation of calls in clownfishes: degree of similarity in closely related species. BMC Evolutionary Biology 11 : 365.