Clownfish live in small groups in symbiosis with a sea anemone. After having shown in 2007 that clownfish aggressive sounds result from the jaw teeth snapping, the researchers at the University of Liège’s Functional and Evolutionary Morphology Laboratory looked into the role played by aggressive and submissive signals in the life styles of clownfishes. Orphal Colleye has thus highlighted the manner in which the acoustic signals produced by these fish could contribute to the regulation of hierarchical relationships in these groups, where each individual, asexual at first, waits its turn before becoming first male and then female. And what about Nemo, then? Alas, the cartoon deceived us!

There exist 29 species of clownfish. Members of the Pomacentridae family, nearly all of them belong to the Amphiprion genus, a single one, ranked in the Premnas genus, being an exception to the rule. Clownfishes meet in the coral reefs in the Indo-Pacific Ocean, where they live in groups in symbiosis with a sea anemone. Their survival depends on this mutualism. Pretty bad swimmers in the majority of cases, they in effect have to confine themselves for most of the time within an adapted shelter, otherwise they risk becoming easy prey.

The anemone is most assuredly adapted to their protection needs, because the clownfish, contrary to their own predators, are immunised against the stinging attacks of its tentacles. Nonetheless, whilst the Clark’s anemonefish (Amphiprion clarkii), for example, is capable of living in a dozen species of sea anemone, others, such as the tomato clownfish (Amphiprion frenatus), can only find asylum in just one of them.

Life in the ‘village’ is pretty peculiar. First of all – but that is not really exceptional – it is the female which wears the trousers. And for good reason: it is her who controls the sex change. Should she die or disappear for whatever reason, her appointed companion, the dominant male, transforms into a female. And that brings about a palace revolution. In fact, around the ‘legitimate couple’ there gravitate a small number of immature fish (four or less, depending on the species) whose gonads are not yet sexually functional. Placed in a hierarchy on the basis of their respective size, these individuals wait their turn in line, ready to climb the rungs of the ladder as their congeners die, leading them to reproduction as a dominant male, then as a female.

As Orphal Colleye, Assistant at the University of Liège’s Department of Biology, Ecology and Evolution and a postdoctoral researcher at the same institution’s Functional and Evolutionary Morphology Laboratory, points out, clownfishes are protandrous hermaphrodites. ‘In other words,’ he says, ‘they have the characteristic of becoming males before being transformed into females later when they reach maturity. They thus distinguish themselves from other species of fish for whom hermaphroditism is protogyneous – the individual first of all acquires female characteristics and then male ones.’

Let’s sum up. In an anemone, one female, one male, and several subordinate immature (non-breeder) individuals. If the female disappears, the male becomes female and the largest  non-breeder becomes male. If it is the male which disappears, the female finds a new ‘partner’ in the person of the largest non-breeder, which will have acquired male characteristics. In these two cases of ‘reconstituted families’ each immature individual climbs the rung of the ladder which should lead it to reproduction.

And what about Nemo, then? Did, the cartoon hoodwink us? Oh yes, cruel disappointment! The sole survivor of eggs laid on the corner of a rock at the foot of the family anemone, the little fish could not have passed its life under the protection of its father after its mother was eaten by a barracuda. No, his father would have become a mother and Nemo himself would have provided her with offspring at the given time...