Cleaner shrimp are true cleaners of injured fish
Reef fishes sustain injuries from various behavioural and environmental interactions. Injured fishes have been observed frequenting cleaning stations to be attended by different cleaner fishes. This symbiotic relationship between injured fishes and cleaner fishes has only been observed in the wild and has never been demonstrated empirically for cleaner shrimp. We present the first investigation of cleaning of injured fish by cleaner shrimp, and the first controlled laboratory trial investigating the functional relationship between injured client fish and cleaners. We tested whether the cleaner shrimp (Lysmata amboinensis) cleaned injured sea goldies (Pseudanthias squamipinnis) following a standardised, unilateral superficial skin lesion. We recorded the cleaning behaviour between shrimp and fish and determined that the fish regulated the cleaning and reduced the amount of cleaning time by the shrimp of the injured side immediately post-injury, corresponding with previous literary evidence of the rapid onset of re-epithelialisation of the injury to seal it in the first 24 h in injured fishes. Thereafter, injured fish showed no cleaning preference between injured and uninjured sides. Image analyses determined that the cleaner shrimp reduced the redness of the injury, representing rubor, associated with the inflammatory response in fishes. Injuries in fishes are susceptible to invasion by secondary pathogens, and the reduction of injury rubor by shrimp may suggest that cleaning by these shrimp could reduce the success of opportunistic infection. Cleaner shrimp neither aggravated existing injury, nor created additional injury, measured quantitatively. The cleaning of injured fish by cleaner shrimp thus likely involves true cleaning behaviour.
DBV was funded through an IPRS (Australian government) scholarship awarded by James Cook University, Townsville, Australia. We are grateful to Cairns Marine, Cairns, Australia, and in particular to Laura Simmons for the ongoing support for our investigations into cleaning symbiosis. We acknowledge the generous assistance of volunteers Alejandro Trujillo González, Thienthanh Trinh, Julian Wilson, and Pauline Narvaez. We thank Peter Waldie and an undisclosed reviewer for their insightful comments and suggestions that ultimately strengthened the manuscript. This paper is dedicated in memoriam to Patrick Donnelly.
Compliance with ethical standards
Statement on the welfare of animals
All applicable international, national and institutional guidelines for the care and use of animals were followed. Animal housing was inspected by the James Cook University welfare officer, and ethics approval was granted prior to commencement of this study under the James Cook University Ethics Committee Permit number A2260, conforming strictly to the national regulations set out in the National Health and Medical Research Council (2013) Australian code for the care and use of animals for scientific purposes, 8th edition, under Section 39 of the National Health and Medical Research Council Act, 1992. A superficial, standardised epithelial injury was necessary to answer the research question. Fish were given a single unilateral superficial injury by removal of scales from a predetermined area on either flank of an area no larger than 0.15 cm2. All fish were housed separately to avoid bullying. Handling of all fish briefly with an aquarium hand-held net was crucial for the transferral into and out of the experimental tanks and could not be avoided. Hand-netting was kept to the operational minimum, occurring only once per day in and out of the experimental tanks per individual. Fish were offered food daily after experimentation and fed successfully, demonstrating a rapid return to normal behaviour after brief handling. Anaesthesia was justifiably employed to facilitate rapid photography of all fish and to avoid prolonged aerial exposure. Three fish mortalities occurred during the experimentation period employing 126 fish. All fish were humanely euthanised after sampling using an anaesthetic overdose of 2-phenoxyethanol (1.5 ml/l > 10 min; Neiffer and Stamper 2009) following the approved animal end-point set out in the animal ethics approval. This article does not contain any studies with human participants performed by any of the authors.
Conflict of interest
The authors declare no conflicts of interest.
All datasets used to generate the statistical analyses are available from https://doi.org/10.4225/28/5b2c885b32331.
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