A publication in Scientific Reports

First evidence of acoustic communication during symbiotic relationships with cleaner fish

17 September 2024

A new study conducted by the University of Liège reveals for the first time the existence of acoustic communication in symbiotic relationships between cleaning fish and their clients. This discovery provides a new perspective on the complex interactions within marine ecosystems.

he symbiosis between cleaner fish and their customers is well known to ethologists. The cleaner fish feed on the ectoparasites present on the bodies of the client fish, thus benefiting from a food source, while the clients benefit from a cleaning that is crucial to their hygiene. However, this relationship is sometimes marred by 'cheating' behaviour, where the cleaners consume the tissues and mucus of the customers instead of the parasites, leading to various repressive and punitive measures on the part of the customer, with the result that the behaviour of the cleaner fish changes as it remembers the exchanges with the various customers.

While understanding types of exchange is often used as a model of interaction in understanding commercial relationships, related studies are based solely on observing the behavioural attitudes of the protagonists. However, a study by researchers at the Functional and Evolutionary Morphology Laboratory has just demonstrated that this symbiotic interaction is also mediated by acoustic communication. Holocentridae fish, also known as squirrelfish and which inhabit coral reefs in the tropical and subtropical regions of the Atlantic, Indian and Pacific oceans, in particular, produce specific sounds to indicate the end of the interaction or to refuse to take part in it," explains Marine Banse, a researcher at ULiège and first author of the article. These sounds are often accompanied by body shaking movements or chases by the cleaning fish."

© Université de Liège / M.Banse

Oscillograms showing an acoustic event produced by Myripristis kuntee during an agonistic interaction with a Labroides cleaner fish (A). The various panels provide information on how the different temporal characteristics were measured: the duration of the event, the number of sounds (S) making up the event, the rhythm, the duration of the sound, the number of pulses (P) in the sound, the pulse periods and the duration of the last pulse. In this example, the acoustic event is made up of 6 sounds (S1-S6). Note that the sounds can be made up of a single pulse (as observed in S1, S4, S5 and S6) or several pulses (as observed in S2 and S3), the latter essentially being repetitions of a single pulse. The enlargement of S1 in (B) shows a sound composed of a single pulse, while the enlargement of S2 in (C) shows a sound composed of several pulses.

Surprisingly, the sounds produced by Holocentridae in this symbiotic context are not stereotyped. Unlike other fish species where sounds vary distinctly according to behavioural context, Holocentridae produce a variety of sounds independently of behaviour or species. Acoustic events can include single or multiple sounds, with short, long or variable pulses," explains Eric Parmetier, director of the Laboratory. This variability calls into question the postulate of sound stereotypy as a function of behavioural context in fish. However, further studies are needed because the type of sound could also be linked to the severity of the client's punishment, something that Marine was unable to determine on the basis of field observations alone".

These results are part of Marine Banse's thesis on the evolutionary patterns of acoustic communication in Holocentridae. Using a multidisciplinary approach combining acoustics, ethology, morphology and phylogeny, this research aims to evaluate and clarify the different types of sound produced by Holocentridae and to establish an evolutionary scenario for their acoustic communication. Thanks to this study, we have had the opportunity to record videos and sounds in the natural environment of these fish, revealing the diversity and non-stereotypy of the sounds produced during symbiotic interactions," enthuses the young researcher.

This study marks a major advance in our understanding of marine symbiotic interactions. The discovery of acoustic communication between cleaner fish and their clients opens up new perspectives for future research into defence and communication mechanisms in the animal kingdom. These innovative results should encourage further studies of acoustic communication in other marine species, enriching our understanding of underwater ecosystem dynamics.