{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T09:14:55Z","timestamp":1790759695004,"version":"4.1.0"},"reference-count":43,"publisher":"The Royal Society","issue":"2052","license":[{"start":{"date-parts":[[2025,8,1]],"date-time":"2025-08-01T00:00:00Z","timestamp":1754006400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/royalsociety.org\/-\/media\/journals\/author\/Licence-to-Publish-20062019-final.pdf"},{"start":{"date-parts":[[2025,8,1]],"date-time":"2025-08-01T00:00:00Z","timestamp":1754006400000},"content-version":"tdm","delay-in-days":0,"URL":"https:\/\/royalsociety.org\/journals\/ethics-policies\/data-sharing-mining\/"}],"funder":[{"DOI":"10.13039\/100022429","name":"Fisheries Society","doi-asserted-by":"crossref","id":[{"id":"10.13039\/100022429","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100003593","name":"National Council for Scientific and Technological Development","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100003593","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100019370","name":"Foundation for Science and Technology","doi-asserted-by":"publisher","id":[{"id":"10.13039\/501100019370","id-type":"DOI","asserted-by":"publisher"}]},{"name":"CNPq\/National Council of Science and Technology"},{"name":"CEEC"}],"content-domain":{"domain":["royalsocietypublishing.org"],"crossmark-restriction":true},"short-container-title":["Proc. R. Soc. B."],"published-print":{"date-parts":[[2025,8]]},"abstract":"<jats:p>\n                    According to the \u2018incentive salience hypothesis\u2019 reward processing involves two main components, including the motivation to obtain a reward (i.e. incentive salience or \u2018wanting\u2019) and the hedonic pleasure felt during its consumption (i.e. hedonic impact or \u2018liking\u2019), which are dissociable. The processing of these hedonic mechanisms is suggested to be mediated by opioid neurotransmission; however, most evidence comes from humans and other mammals. Here we argue that, in mutualistic associations, client fish seek to interact with cleaner fish not only due to the immediate benefits of being cleaned but also because of the hedonic impact of tactile stimulation, modulated by the opioid system. We used a conditioned place preference (CPP) paradigm to test the hedonic dimension of motivation to be cleaned and found that de-parasitized client fish (the butterflyfish\n                    <jats:italic toggle=\"yes\">Chaetodon auriga<\/jats:italic>\n                    ) preferred the compartment paired with cleaner fish (\n                    <jats:italic toggle=\"yes\">Labroides dimidiatus<\/jats:italic>\n                    ). Treatment with the \u03bc-opioid receptor agonist The \u00b5-opioid receptor agonist 2-Ala-4-mephe-5-gly-enkephalin (DAMGO) dose-dependently increased preference, while treatment with the antagonist naloxone decreased it. To test for fish incentive salience, we used a detour task, with barriers being added after each trial to demand higher response strength to reach the target and found that client fish can circumvent barriers to reach a cleaner-adjacent compartment. Response strength (number of barriers added before \u2018giving up\u2019) was not affected by treatment with either naloxone or DAMGO. Our results show that cleaner\u2013client interactions are hedonically positive for clients, an effect that is mediated by the opiodergic system. Visual contact with cleaners is sufficient to activate incentive salience programmes, but no evidence of participation of the opioidergic system in these programmes was found. Overall, we provide the first evidence confirming the participation of the opioidergic system in motivation to be cleaned in mutualistic associations.\n                  <\/jats:p>","DOI":"10.1098\/rspb.2025.1532","type":"journal-article","created":{"date-parts":[[2025,8,12]],"date-time":"2025-08-12T23:06:26Z","timestamp":1755039986000},"update-policy":"https:\/\/doi.org\/10.1098\/crossmark-policy","source":"Crossref","is-referenced-by-count":4,"title":["The hedonic impact of cleaner\u2013client fish interactions is mediated by the opioid system"],"prefix":"10.1098","volume":"292","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3261-9196","authenticated-orcid":true,"given":"Caio","family":"Maximino","sequence":"first","affiliation":[{"name":"Laboratory of Neurosciences and Behavior \u201cFrederico Guilherme Graeff\u201d, Faculty of Psychology, Institute of Health and Biological Studies, Federal University of the South and Southeast of Par\u00e1, Marab\u00e1 68500-000, Brazil"},{"name":"Research Group on Neurosciences, Behavior &amp; Cognition, Federal University of the South and Southeast of Par\u00e1, Marab\u00e1 68500-000, Brazil"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3868-866X","authenticated-orcid":true,"given":"Heloysa","family":"Araujo-Silva","sequence":"additional","affiliation":[{"name":"FishLab, Department of Physiology and Behavior, Federal University of Rio Grande do Norte, Natal 59078-900, Brazil"},{"name":"Graduate Program in Psychobiology, Biosciences Center, Federal University of Rio Grande do Norte, Natal 59078-900, Brazil"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-4693-1946","authenticated-orcid":true,"given":"In\u00eas","family":"Cacela-Rodrigues","sequence":"additional","affiliation":[{"name":"CIBIO, Research Centre in Biodiversity and Genetic Resources, University of Porto, InBIO Associate Laboratory, Vair\u00e3o, Porto 4485-661, Portugal"},{"name":"BIOPOLIS Program in Genomics, Biodiversity and Land Planning, Research Centre in Biodiversity and Genetic Resources, Campus of Vair\u00e3o, Vair\u00e3o 4485-661, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3294-7859","authenticated-orcid":true,"given":"Ana C.","family":"Luchiari","sequence":"additional","affiliation":[{"name":"FishLab, Department of Physiology and Behavior, Federal University of Rio Grande do Norte, Natal 59078-900, Brazil"},{"name":"Graduate Program in Psychobiology, Biosciences Center, Federal University of Rio Grande do Norte, Natal 59078-900, Brazil"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8891-8881","authenticated-orcid":true,"given":"Jo\u00e3o L.","family":"Saraiva","sequence":"additional","affiliation":[{"name":"Fish Etho Group Association, Faro 8005-226, Portugal"},{"name":"Center of Marine Sciences (CCMAR\/CIMAR LA), 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