Labroides Dimidiatus Research Articles

Cleaner fish with mirror self-recognition capacity precisely realize their body size based on their mental image

Animals exhibiting mirror self-recognition (MSR) are considered self-aware; however, studies on their level of self-awareness remain inconclusive. Recent research has indicated the potential for cleaner fish (Labroides dimidiatus) to possess a sophisticated level of private self-awareness. However, as this study revealed only an aspect of private self-awareness, further investigation into other elements is essential to substantiate this hypothesis. Here, we show that cleaner fish, having attained MSR, construct a mental image of their bodies by investigating their ability to recall body size. A size-based hierarchy governs the outcomes of their confrontations. The mirror-naïve fish behaved aggressively when presented with photographs of two unfamiliar conspecifics that were 10% larger and 10% smaller than their body sizes. After passing the MSR test, they refrained from aggression toward the larger photographs but still behaved aggressively toward the smaller ones without re-examining their mirror images. These findings suggest that cleaner fish accurately recognize their body size based on mental images of their bodies formed through MSR. Additionally, mirror-experienced fish frequently revisited the mirror when presented with an intimidating larger photograph, implying the potential use of mirrors for assessing body size. Our study established cleaner fish as the first non-human animal to be demonstrated to possess private self-awareness.

Learning competence of the temperate facultative cleaner wrasse Thalassoma pavo (Labridae).

Cleaner fishes remove parasites from other fishes called "clients," thereby contributing to a healthier ecosystem. Although the behavior and learning abilities of dedicated and tropical cleaner fishes have been broadly studied, a limited number of studies investigated the behavior of facultative and temperate cleaner fishes and, to the best of our knowledge, none focused on their cognitive abilities. Here, we tested the learning abilities of a species of temperate facultative cleaner, the ornate wrasse Thalassoma pavo in laboratory conditions, based on two problems. These two problems, or tasks, are relevant in two different contexts: the first one, deemed as mutualistically relevant, the cue-based discrimination task, and the second one, the spatial-based discrimination task, which is relevant in a non-cleaning context, when fish navigate through their environment to find food and return to their territories. We found that T. pavo individuals were able to solve these two tasks but excelled at the spatial task rather than with the cue discrimination. The same individuals were also challenged to learn the reverse protocol of these tasks and were again most successful in learning the reverse spatial discrimination problem, but not the cue. Contrary to the dedicated cleaner wrasse Labroides dimidiatus, this temperate facultative cleaner wrasse is slower to learn mutualistic relevant problems but competent in solving spatially derived problems. This may be due to the specific demands of their socio-ecological environment, with facultative cleaners having a greater component of non-mutualistic skills (spatial component), which prepares them to search for alternative food sources if necessary (e.g., feeding on the substrate) or even to expand territories more easily and less prepared to deal with mutualistic exchanges compared to dedicated cleaners that specialize to become increasingly socially competent.

Cleaner gobies can solve a biological market task when the correct cue is larger

Animal cognition is deeply influenced by interactions with the environment. A notable example of sophisticated cognition in the animal kingdom is described by the mutualistic relationship between cleaner fish and clients, where decision-making processes play a pivotal role in partner choice and fish survival. In this context, while extensive research has explored the cognition of the cleaner wrasse Labroides dimidiatus, it is important to note that studies on the cognition of other wrasse species and on its Caribbean counterparts, Elacatinus spp., are limited. Therefore, to extend our comprehension of cognition in cleaner fish with different evolutionary backgrounds, it is important to focus our attention on the genus Elacatinus spp. In this study, we used plexiglass plates as surrogates for clients and assessed the ability of cleaner gobies, Elacatinus oceanops, to solve a biological market task where prioritizing an ephemeral food plate over a permanent one would double the food reward. We varied cue-based decision-making using both ecologically relevant cues (plate, size, and color) and non-relevant ones (presentation side). Additionally, we tested their capacity for reversal learning, an indicator of complex cognitive abilities. Notably, cleaner gobies were able to solve the biological markets task when the distinguishing cue was a larger plate size. Given that these gobies tend to prioritize larger predatory clients in nature, our results align with their natural inclination. Consequently, further research, including studies involving wild individuals, is essential to elucidate the cognitive abilities of the studied species and their implications in the ecological context and evolutionary history.

Behavior, site use and demographics of shortfin devil rays, Mobula kuhlii, at a newly-discovered cleaning area in South Africa

Many shark and ray species show affinity to specific sites, making these areas critical for their survival. These include cleaning stations: locations on reefs where cleaner fish remove parasites and clean wounds, which is important for maintaining health. Cleaning stations also function as social gathering sites, or resting points, where courtship and mating can occur. In this study, we identify an aggregation site for the shortfin devil ray, Mobula kuhlii (Family Mobulidae) within the Aliwal Shoal Marine Protected Area in KwaZulu-Natal (KZN), South Africa, and document their behavior. Remote underwater video was used to collect footage of M. kuhlii being cleaned by blue streak cleaner wrasse, Labroides dimidiatus. Generalized additive models (GAMs) were used to assess environmental predictors of M. kuhlii presence on Aliwal Shoal. Mixed models were used to assess the same environmental predictors and their correlation with mean M. kuhlii cleaning duration and number of L. dimidiatus bites per second at the identified cleaning station site. M. kuhlii were present in 56% of observation days, with group numbers up to > 150 individuals. Sea surface temperature was a significant predictor for M. kuhlii presence, while a north to south current was significantly associated with longer mean cleaning durations. These results support findings of mobulid studies in KZN that show increased habitat use during summer temperatures (24–25 °C) and suggest these sites to be important for individual health and social interaction. We hope these findings can be used for development of location-specific management plans to safeguard this Endangered species.

Neuromolecular responses in disrupted mutualistic cleaning interactions under future environmental conditions

BackgroundMutualistic interactions, which constitute some of the most advantageous interactions among fish species, are highly vulnerable to environmental changes. A key mutualistic interaction is the cleaning service rendered by the cleaner wrasse, Labroides dimidiatus, which involves intricate processes of social behaviour to remove ectoparasites from client fish and can be altered in near-future environmental conditions. Here, we evaluated the neuromolecular mechanisms behind the behavioural disruption of cleaning interactions in response to future environments. We subjected cleaner wrasses and surgeonfish (Acanthurus leucosternon, serving as clients) to elevated temperature (warming, 32 °C), increased levels of CO2 (high CO2, 1000 ppm), and a combined condition of elevated CO2 and temperature (warming and high CO2, 32 °C, and 1000 ppm) for 28 days.ResultsEach of these conditions resulted in behavioural disruptions concerning the motivation to interact and the quality of interaction (high CO2 − 80.7%, warming − 92.6%, warming and high CO2 − 79.5%, p < 0.001). Using transcriptomics of the fore-, mid-, and hindbrain, we discovered that most transcriptional reprogramming in both species under warming conditions occurred primarily in the hind- and forebrain. The associated functions under warming were linked to stress, heat shock proteins, hypoxia, and behaviour. In contrast, elevated CO2 exposure affected a range of functions associated with GABA, behaviour, visual perception, thyroid hormones and circadian rhythm. Interestingly, in the combined warming and high CO2 condition, we did not observe any expression changes of behaviour. However, we did find signs of endoplasmic reticulum stress and apoptosis, suggesting not only an additive effect of the environmental conditions but also a trade-off between physiological performance and behaviour in the cleaner wrasse.ConclusionsWe show that impending environmental shifts can affect the behaviour and molecular processes that sustain mutualistic interactions between L. dimidiatus and its clients, which could have a cascading effect on their adaptation potential and possibly cause large-scale impacts on coral reef ecosystems.

Punishment is sensitive to outside options in humans but not in cleaner fish (Labroides dimidiatus)

Punishment is sensitive to outside options in humans but not in cleaner fish (Labroides dimidiatus)

Gene losses, parallel evolution and heightened expression confer adaptations to dedicated cleaning behaviour

BackgroundCleaning symbioses are captivating interspecific interactions in which a cleaner fish removes ectoparasites from its client, contributing to the health and diversity of natural fish communities and aquaculture systems. However, the genetic signatures underlying this specialized behaviour remain poorly explored. To shed light on this, we generated a high-quality chromosome-scale genome of the bluestreak cleaner wrasse Labroides dimidiatus, a dedicated cleaner with cleaning as primary feeding mechanism throughout its life.ResultsCompared with facultative and non-cleaner wrasses, L. dimidiatus was found with notable contractions in olfactory receptors implying their limited importance in dedicated cleaning. Instead, given its distinct tactile pre-conflict strategies, L. dimidiatus may rely more heavily on touch sensory perception, with heightened gene expression in the brain in anticipation of cleaning. Additionally, a reduction in NLR family CARD domain-containing protein 3 might enhance innate immunity of L. dimidiatus, probably assisting to reduce the impacts from parasite infections. In addition, convergent substitutions for a taste receptor and bone development genes across cleaners (L. dimidiatus and facultative cleaners) may provide them with evolved food discrimination abilities and jaw morphology that differentiate them from non-cleaners. Moreover, L. dimidiatus may exhibit specialized neural signal transductions for cleaning, as evidenced by positive selection in genes related to the glutamatergic synapse pathway. Interestingly, numerous glutamate receptors also demonstrated significantly higher expression in L. dimidiatus not engaged in cleaning, as compared to those involved in cleaning. Besides, apparent contractions in L. dimidiatus for protocadherins, which are responsible for neuronal development, may further promote specialized neural signal transductions in this species.ConclusionsThis study reveals that L. dimidiatus harbours substantial losses in specific gene families, convergent evolutions across cleaners and a large-scale high gene expression in preparation for cleaning, allowing for adaptation to the dedicated cleaning behaviour.

In the absence of extensive initial training, cleaner wrasse Labroides dimidiatus fail a transitive inference task.

Transitive inference (TI) is a reasoning capacity that allows individuals to deduce unknown pair relationships from previous knowledge of other pair relationships. Its occurrence in a wide range of animals, including insects, has been linked to their ecological needs. Thus, TI should be absent in species that do not rely on such inferences in their natural lives. We hypothesized that the latter applies to the cleaner wrasse Labroides dimidiatus and tested this with 19 individuals using a five-term series (A > B > C > D > E) experiment. Cleaners first learned to prefer a food-rewarding plate (+) over a non-rewarding plate (-) in four plate pairs that imply a hierarchy from plate A to plate E (A+B-, B+C-, C+D-, D+E-), with the learning order counterbalanced between subjects. We then tested for spontaneous preferences in the unknown pairs BD (transitive inference task) and AE (as a control for anchors), interspersed between trials involving a mix of all known adjacent pairs. The cleaners systematically preferred A over E and showed good performance for A+B- and D+E- trials. Conversely, cleaners did not prefer B over D. These results were unaffected by the reinforcement history, but the order of learning of the different pairs of plates had a main impact on the remembrance of the initial training pairs. Overall, cleaners performed randomly in B+C- and C+D- trials. Thus, a memory constraint may have prevented subjects from applying TI. Indeed, a parallel study on cleaner wrasse provided positive evidence for TI but was achieved following extensive training on the non-adjacent pairs which may have over-ridden the ecological relevance of the task.

Not so monochromatic: Size-dependency of both sex and color in the cleaner wrasse Labroides dimidiatus

In marine interspecific cleaning mutualisms, small fish known as “cleaners” inspect the surface, gills and sometimes the mouth of “client” reef fish, eating ectoparasites, mucus, scales and dead or infected tissue. These cleaner fish species share similar vivid coloration that makes them recognizable by clients. To gain insight on additional communication roles of cleaner fish color, we tested if differences in color among cleaner wrasse Labroides dimidiatus individuals captured from the wild are explained by sex, body size or parasite loads. We found that males were larger, heavier and tended to have more saturated blue tails than females. We also found blue color saturation to be positively correlated with size, and that this size-dependence explains the trend for the sexes to differ in color. Parasite loads did not predict individual differences in color, but fish in our sample were not heavily parasitized. Other color traits (including yellow color saturation and black color brightness) did not differ between the sexes and were associated with morphological differences. Size-dependence of blue color may thus suggest that it is a condition-dependent signal that could be used in various types of inter- and intraspecific social interactions.

A marine cleaning mutualism provides new insights in biological market dynamics.

Most mutually beneficial social interactions (cooperation within species, mutualism between species) involve some degree of partner choice. In an analogy to economic theory as applied to human trading practices, biological market theory (BMT) focuses on how partner choice affects payoff distributions among non-human traders. BMT has inspired a great diversity of research, including research on the mutualism between cleaner fish Labroides dimidiatus and other marine fish, their 'clients'. In this mutualism, clients have ectoparasites removed and cleaners obtain food in return. We use the available data on L. dimidiatus cleaner-client interactions to identify avenues for future expansion of BMT. We focus on three main topics, namely how partner quality interacts with supply-to-demand ratios to affect service quality, the role of threats and forms of forceful intervention, and the potential role of cognition. We consider it essential to identify the specifics of each biological market as a basis for the development of more sophisticated BMT models. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.

Do Cleaner Fish (Labroides dimidiatus) Have General Cognitive Ability? A Reanalysis of Individual Differences Data and Consideration of Phylogenetic Context

Do Cleaner Fish (Labroides dimidiatus) Have General Cognitive Ability? A Reanalysis of Individual Differences Data and Consideration of Phylogenetic Context

Cleaner fish recognize self in a mirror via self-face recognition like humans

Some animals have the remarkable capacity for mirror self-recognition (MSR), yet any implications for self-awareness remain uncertain and controversial. This is largely because explicit tests of the two potential mechanisms underlying MSR are still lacking: mental image of the self and kinesthetic visual matching. Here, we test the hypothesis that MSR ability in cleaner fish, Labroides dimidiatus, is associated with a mental image of the self, in particular the self-face, like in humans. Mirror-naive fish initially attacked photograph models of both themselves and unfamiliar strangers. In contrast, after all fish had passed the mirror mark test, fish did not attack their own (motionless) images, but still frequently attacked those of unfamiliar individuals. When fish were exposed to composite photographs, the self-face/unfamiliar body were not attacked, but photographs of unfamiliar face/self-body were attacked, demonstrating that cleaner fish with MSR capacity recognize their own facial characteristics in photographs. Additionally, when presented with self-photographs with a mark placed on the throat, unmarked mirror-experienced cleaner fish demonstrated throat-scraping behaviors. When combined, our results provide clear evidence that cleaner fish recognize themselves in photographs and that the likely mechanism for MSR is associated with a mental image of the self-face, not a kinesthetic visual-matching model. Humans are also capable of having a mental image of the self-face, which is considered an example of private self-awareness. We demonstrate that combining mirror test experiments with photographs has enormous potential to further our understanding of the evolution of cognitive processes and private self-awareness across nonhuman animals.

Species diversity and DNA barcoding of wrasses (Teleostei: Labridae) along the southwest coast of India

Wrasses are among the most interesting and numerically abundant fish families and are widely distributed in deep and coastal marine waters. A survey was undertaken to study the diversity of labrids along the southwest coast of India between December 2020 to January 2022. A total of 98 specimens belonging to the family Labridae were collected during the study period, including nine species classified under five genera. The species included Cheilinus chlorourus, Halichoeres timorensis, Halichoeres marginatus, Halichoeres zeylonicus, Labroides dimidiatus, Stethojulis trilineata, Stethojulis interrupta, Thalassoma lunare and Thalassoma jansenii. The species were identified through morphological studies and DNA barcoding using the mitochondrial cytochrome oxidase I (COI) gene. The analyses aimed to document the morphological and molecular variations of species from different localities. The resultant molecular data were compared with morphological identifications and additional sequence data from GenBank. The results concluded that generated mtDNA sequences of wrasses matched closely with the available sequences in the GenBank. The studied species were nested in clades with the nearest related species with low Pairwise distances. The study recommends stock assessment of the labrids of India, as they are heavily exploited for both as food and ornamental fish species.

Comparison of mortality and feeding behavior of the false cleanerfish Aspidontus taeniatus and the lance blenny A. dussumieri regarding the effects of mimicry.

The online version contains supplementary material available at 10.1007/s10164-022-00769-8.

Indirect effects of cleaner fish Labroides dimidiatus on fish grazing per reef area and benthic community structure

Grazing fishes farm algae, and consume algae, detritus and sediment and consequently differentially modify benthic communities. Manipulations of cleaner fish Labroides dimidiatus on reefs show that cleaners affect fish abundance differently according to grazer functional group. Accordingly, whether reefs are grazed differently, with consequences for the benthos (fouling material tile−1), was tested using reefs kept free of L. dimidiatus for 10 years compared with undisturbed control reefs. We recorded on video the grazing density (bites tile−1 h−1 reef−1) on settlement tiles and the natural benthos (roving fishes only), according to territorial algal farmer (Pomacentridae) and roving grazer (Acanthuridae, Labridae, Siganidae) functional groups, and measured the accumulation of fouling material tile−1 after 10 months. Grazing density on tiles (dominated by ‘indeterminate’ farmers, and roving ‘sediment-removing’ detritivore Ctenochaetus striatus) and the natural benthos (dominated by Ct. striatus and other grazers) was not measurably affected by cleaner presence. The composition of fouling material (dominated by detritus > turf algae > sediment > other) and organic and inorganic dry weight of material tile−1 were also not measurably affected by cleaner presence. This points to resilience of the benthic community to loss of cleaners. The likely complex interactions between cleaner fish presence, grazer abundance and mobility, and the often-opposite effects of territorial farmers and roving grazers on the benthos underscore the challenge in determining indirect effects of cleaners on benthic community structure. However, a lack of cleaners has negative ramifications for fish populations and physiology and thus their loss remains problematic for client fishes.

Bluestreak cleaner wrasse are unsuspecting parasite super-spreaders

Personal hygiene matters, whether it's preening or taking a shower. But some creatures are unable to maintain their own cleanliness, so fish subcontract out their sanitation to smaller fish that nibble at lice on their skin. ‘Cleaner fish may clean throughout their entire lifespan, using cleaning as their primary way of acquiring food, or engage in cleaning interactions predominantly as juveniles or as a secondary source of food’, says Pauline Narvaez from James Cook University, Australia. However, Narvaez and Kate Hutson (James Cook University) wondered whether there was a darker side to the symbiotic hygiene story. Could cleaner fish unintentionally carry and transmit to unsuspecting clients some of the parasites that they usually vacuum up? Intrigued by the possibility that cleaner fish could be inadvertent parasite super-spreaders, Narvaez and Hutson joined forces with Renato Morais (James Cook University), David Vaughan (Central Queensland University, Australia) and Alexandra Grutter (The University of Queensland, St Lucia, Australia) to find out whether bluestreak cleaner wrasse (Labroides dimidiatus) are vulnerable to infection by the pests upon which they usually feast. Venturing out onto the Great Barrier Reef at Lizard Island, Australia, Narvaez and Morais went in search of bluestreak cleaner wrasse, armed with barrier- and hand-nets. ‘Once the cleaner fish were caught, we gently moved them into plastic bags until we got back to the research station’ says Narvaez. She then released five famished parasitic juvenile gnathiid isopod crustaceans (Gnathia aureamaculosa) into each tank with an individual wrasse to find out how succulent the cleaner fish were for the parasites. Back at James Cook University, Narvaez also isolated cleaner wrasse with juvenile parasitic protozoans (Cryptocaryon irritans), which cause marine white spot disease, and parasitic flatworm larvae (Neobenedenia girellae), which attach to their host's body, to find out how susceptible the fish were to other infections.Impressively, the cleaner wrasse were remarkably resistant to both white spot disease and the parasitic flatworms; however, the juvenile parasitic crustacean larvae were able to grab a hold on the cleaner wrasses’ skin. So bluestreak cleaner wrasse aren't completely immune to freely swimming juvenile parasites, although they seem to be less vulnerable than other similarly sized species. But how susceptible might the wrasse be to adult parasites, carried by their clients, while going about their day job?This time, Narvaez dextrously transferred adult flat worms to healthy bluestreak cleaner wrasse to find out how the parasitic flatworms fared on the cleaning professionals. Impressively, the flatworms managed to hold on to their cleaner wrasse rides for the first 24 h, although roughly half detached in the following 24 h; the adult parasites are able to cling on long enough to reach their next host. Fortunately, when Narvaez monitored the number of eggs released by the parasitic N. girellae hitch-hikers, she found they weren't as fertile as when catching a lift on their usual hosts, initially producing only a fraction (7%) of the eggs that they usually release, falling to virtually zero by the end of the week.‘Some parasites may have evolved to exploit cleaning symbiosis as a mechanism for transmission’, says Narvaez, explaining that the flexible flatworms, which shuffle about on their host's skin, could hop off their L. dimidiatus ride as the wrasse burrows about in the gills of another client to infect it. And, as bluestreak cleaner wrasse provide hygiene services to approximately 2300 fish each day, Narvaez and colleagues suspect that infected cleaners could be contributing unwittingly to the problem.

Cleaner fish are potential super-spreaders.

Cleaning symbiosis is critical for maintaining healthy biological communities in tropical marine ecosystems. However, potential negative impacts of mutualism, such as the transmission of pathogens and parasites during cleaning interactions, have rarely been evaluated. Here, we investigated whether the dedicated bluestreak cleaner wrasse, Labroides dimidiatus, is susceptible to and can transmit generalist ectoparasites between client fish. In laboratory experiments, L. dimidiatus were exposed to infective stages of three generalist ectoparasite species with contrasting life histories. Labroides dimidiatus were susceptible to infection by the gnathiid isopod Gnathia aureamaculosa, but were significantly less susceptible to the ciliate protozoan Cryptocaryon irritans and the monogenean flatworm Neobenedenia girellae, compared with control host species (Coris batuensis or Lates calcarifer). The potential for parasite transmission from a client fish to the cleaner fish was simulated using experimentally transplanted mobile adult (i.e. egg-producing) monogenean flatworms on L. dimidiatus. Parasites remained attached to cleaners for an average of 2days, during which parasite egg production continued, but was reduced compared with that on control fish. Over this timespan, a wild cleaner may engage in several thousand cleaning interactions, providing numerous opportunities for mobile parasites to exploit cleaners as vectors. Our study provides the first experimental evidence that L. dimidiatus exhibits resistance to infective stages of some parasites yet has the potential to temporarily transport adult parasites. We propose that some parasites that evade being eaten by cleaner fish could exploit cleaning interactions as a mechanism for transmission and spread.

Access to Cleaning Services Alters Fish Physiology Under Parasite Infection and Ocean Acidification.

Cleaning symbioses are key mutualistic interactions where cleaners remove ectoparasites and tissues from client fishes. Such interactions elicit beneficial effects on clients’ ecophysiology, with cascading effects on fish diversity and abundance. Ocean acidification (OA), resulting from increasing CO2 concentrations, can affect the behavior of cleaner fishes making them less motivated to inspect their clients. This is especially important as gnathiid fish ectoparasites are tolerant to ocean acidification. Here, we investigated how access to cleaning services, performed by the cleaner wrasse Labroides dimidiatus, affect individual client’s (damselfish, Pomacentrus amboinensis) aerobic metabolism in response to both experimental parasite infection and OA. Access to cleaning services was modulated using a long-term removal experiment where cleaner wrasses were consistently removed from patch reefs around Lizard Island (Australia) for 17 years or left undisturbed. Only damselfish with access to cleaning stations had a negative metabolic response to parasite infection (maximum metabolic rate—ṀO2Max; and both factorial and absolute aerobic scope). Moreover, after an acclimation period of 10 days to high CO2 (∼1,000 µatm CO2), the fish showed a decrease in factorial aerobic scope, being the lowest in fish without the access to cleaners. We propose that stronger positive selection for parasite tolerance might be present in reef fishes without the access to cleaners, but this might come at a cost, as readiness to deal with parasites can impact their response to other stressors, such as OA.

Cleaner Fish Labroides dimidiatus Presence Does Not Indirectly Affect Demersal Zooplankton

Coral reef mutualisms involve complex trophic ecological relationships that produce indirect effects. Excluding mutualistic cleaner fish Labroides dimidiatus from reefs indirectly increases the abundance of many fishes and reduces demersal stages of their ectoparasitic prey (gnathiid isopods). Whether cleaners affect populations of planktivorous fishes that consume demersal zooplankton, and consequently indirectly affect the rest of the demersal zooplankton community — via presumed changes in planktivory — is unknown. Therefore, using a long-term cleaner fish manipulation on patch reefs (July 2000 to December 2012, Great Barrier Reef), we tested whether cleaner treatment (removal or control) affects planktivorous fish abundance and diversity, and demersal zooplankton biomass, abundance, and diversity. Fish surveys, 9 and 12 years after removing cleaners revealed fewer fish on removal compared to control reefs for one of the three most abundant planktivores, but not total abundance (Pomacentridae, 26 species), diversity, and composition. Emerging zooplankton were sampled during the day and night over nine sampling trips across 12 years. There was no effect of cleaner treatment on post-removal values, compared with pre-removal values in July 2000, for zooplankton biomass, abundance, diversity, and composition (34 taxa). Zooplankton abundance showed no diel differences, but diversity, and occasionally biomass, were higher at night. Zooplankton composition also showed diel differences, with three taxa contributing the most to this dissimilarity [Cirripeda nauplii, Facetotecta (Arthopoda), Oikopleuridae (Chordata)]. Zooplankton diversity did not differ among times, abundance was higher in January 2002 relative to July 2000, and composition differed among all times. The lack of detectable indirect effects of cleaner fish presence on zooplankton (non-gnathiid) may partly be due to cleaners’ variable effect on planktivorous fish abundance, but also the result of invertebrate planktivory and other processes that affect zooplankton populations not investigated here. Nevertheless, the pronounced diel and temporal changes in zooplankton observed likely influence coral reef trophic interactions.

Neuro-molecular characterization of fish cleaning interactions

Coral reef fish exhibit a large variety of behaviours crucial for fitness and survival. The cleaner wrasse Labroides dimidiatus displays cognitive abilities during interspecific interactions by providing services of ectoparasite cleaning, thus serving as a good example to understand the processes of complex social behaviour. However, little is known about the molecular underpinnings of cooperative behaviour between L. dimidiatus and a potential client fish (Acanthurus leucosternon). Therefore, we investigated the molecular mechanisms in three regions of the brain (Fore-, Mid-, and Hindbrain) during the interaction of these fishes. Here we show, using transcriptomics, that most of the transcriptional response in both species was regulated in the Hindbrain and Forebrain regions and that the interacting behaviour responses of L. dimidiatus involved immediate early gene alteration, dopaminergic and glutamatergic pathways, the expression of neurohormones (such as isotocin) and steroids (e.g. progesterone and estrogen). In contrast, in the client, fewer molecular alterations were found, mostly involving pituitary hormone responses. The particular pathways found suggested synaptic plasticity, learning and memory processes in the cleaner wrasse, while the client indicated stress relief.