How do cleaner fish choose their clients?

MARE researchers Madalena Rannuci, Melanie Tribunal, Beatriz Pereira Daniele Romeo and José Ricardo Paula are the authors of the article ‘Cleaner gobies can solve a biological market task when the correct cue is larger’, recently published in the scientific journal Frontiers. The article studies the ability of cleaner gobies to solve a biological market task where prioritising an ephemeral food dish over a permanent one would double the food reward.

Due to their complex structure, high biodiversity and fluctuating environmental conditions, coral reefs present unique challenges that require the development of adaptive strategies and specialised skills to ensure survival. Although little known, fish have highly developed cognitive abilities, which are evident in mutualistic relationships, such as the one established between cleaner fish and their clients. In these situations, there is an ability to prioritise certain interactions over others, which suggests cognitive sophistication due to the complex social decision-making process involved.

In the Caribbean, the cleaning gobies Elacatinus spp. play a fundamental role in ecosystems through mutualistic cleaning relationships, which they establish with a huge variety of species, including predators. Despite this, the cognitive capacity of fish of this species to choose clients has been little studied.

In this context, a team of researchers from MARE assessed the cognitive abilities of cleaner gobies, specifically their decision-making skills and learning capacity, by testing their ability to solve a ‘customer’ choice task. In the study, the researchers used acrylic plates in place of ‘customers’ and assessed the ability of cleaner gobies, Elacatinus oceanops , to solve a biological market task where prioritising an ephemeral food dish over a permanent one would double the food reward. In addition, they varied their decision-making based on cues, using both ecologically relevant cues (plate, size and colour) and non-relevant cues (presentation side). In addition, their reversal learning ability was tested, an indicator of complex cognitive abilities.

With this study, the researchers were able to verify that cleaner gobies were able to solve the biological markets task when the distinctive cue was a larger plate size to the detriment of other cues such as colour. This leads to the conclusion that these fish prioritise predatory clients, generally characterised by larger body sizes. Prioritising predators helps gobies to reduce the negative impact of a potential threat to other fish, encouraging customers to return promptly and facilitating the mutualistic exchange of benefits.

To read the article click HERE

(Cover photo by AlgaeBarn)