The ability of teleost fishes to recognize individual faces suggests an early evolutionary origin in vertebrates.

The face is the most important area on the human body for visually differentiating between individuals. When encountering another person, humans initially gaze at and perceive the face holistically, utilizing relational information and specific neural systems. Information such as identity and emotional state are then obtained from the face by distinguishing between small inter-individual differences, i.

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.

Male Guppies Recognize Familiar Conspecific Males by Their Face.

Individual recognition is a necessary cognitive ability for the maintenance of stable social relationships. Recent studies have shown that like primates, some fish species can distinguish familiar fish from unfamiliar strangers via face-recognition. However, the taxa of the studied fish species are restricted (within Perciformes) and the visual signal used for the recognition of fish remains unclear.

Further evidence for the capacity of mirror self-recognition in cleaner fish and the significance of ecologically relevant marks.

An animal that tries to remove a mark from its body that is only visible when looking into a mirror displays the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness. Conservative interpretations of existing data conclude that convincing evidence for MSR is currently restricted to great apes. Here, we address proposed shortcomings of a previous study on MSR in the cleaner wrasse Labroides dimidiatus, by varying preexposure to mirrors and by marking individuals with different colors.

Age- and sex-dependent variation in relatedness corresponds to reproductive skew, territory inheritance, and workload in cooperatively breeding cichlids.

Kin selection plays a major role in the evolution of cooperative systems. However, many social species exhibit complex within-group relatedness structures, where kin selection alone cannot explain the occurrence of cooperative behavior. Understanding such social structures is crucial to elucidate the evolution and maintenance of multi-layered cooperative societies.

Prosocial and antisocial choices in a monogamous cichlid with biparental care.

Human society is cooperative and characterized by spontaneous prosociality. Comparative studies on endotherm vertebrates suggest that social interdependence causes the evolution of proactive prosociality. To test the generality of this hypothesis, we modify a prosocial choice task for application to the convict cichlid, Amatitlania nigrofasciata, a monogamous fish with biparental care and a strong pair bond.

Transitive inference in cleaner wrasses (Labroides dimidiatus).

Transitive inference (TI) is the ability to infer unknown relationships from previous information. To test TI in non-human animals, transitive responding has been examined in a TI task where non-adjacent pairs were presented after premise pair training. Some mammals, birds and paper wasps can pass TI tasks.

Sperm Allocation Strategies Depending on Female Quality in Medaka ().

Sperm production is costly, and males are expected to strategically allocate this potentially limiting resource to maximize their fitness. Sperm allocation theory predicts that males should adjust their sperm expenditure in relation to female quality. However, the available empirical evidence is limited.

Fish focus primarily on the faces of other fish.

"Face" is a special stimulus in humans and, nonhuman primates, and some other social mammals; that is, they perceive the face differently from the other body parts and other stimuli. In these species, the face conveys much information, so individuals examine the face at first sight rather than other body parts. Similar to mammals, the faces of fish also convey much information, but little is known about whether fish pay attention to the face or face-viewing patterns.

Do Scales of the Cichlid in Lake Tanganyika Function as a Morphological Defense Against Scale-Eating?

Many cichlid species in the shallow-shore of Lake Tanganyika suffer damage from attacks by the scale-eater . Many prey fish engage in warning behaviors to this predator. It has been hypothesized that, if prey fish have difficulty employing such behavioral tactics, morphological defenses against scale-eating, such as hard scales, will evolve.

If a fish can pass the mark test, what are the implications for consciousness and self-awareness testing in animals?

Abstract: The ability to perceive and recognise a reflected mirror image as self (mirror self-recognition, MSR) is considered a hallmark of cognition across species. Although MSR has been reported in mammals and birds, it is not known to occur in any other major taxon. Potentially limiting our ability to test for MSR in other taxa is that the established assay, the mark test, requires that animals display contingency testing and self-directed behaviour.

Does a cichlid fish process face holistically? Evidence of the face inversion effect.

Faces are the most important body part for differentiating among human individuals by humans. Humans read the face as a whole, rather than looking at its parts, which makes it more difficult to recognise inverted faces than upright. Some other mammals also identify each other based on the upright face and take longer to recognise inverted faces.

Variations in the breeding behavior of cichlids and the evolution of the multi-functional seminal plasma protein, seminal plasma glycoprotein 120.

Background: Seminal plasma proteins are associated with successful fertilization. However, their evolutionary correlation with fertilization mechanisms remains unclear. Cichlids from Lake Tanganyika show a variety-rich spawning behavior that is associated with the transfer of the sperm to the egg for fertilization.

A social cichlid fish failed to pass the mark test.

Since the pioneering work in chimpanzees, mirror self-recognition (MSR), the ability to recognise oneself in a mirror, has been reported in great apes, Asian elephants, dolphins, and some social birds using the mark test, in which animals that possess MSR touch an imperceptible mark on their own bodies only when a mirror is present. However, giant pandas, which are solitary, failed to pass the mark test, suggesting that MSR evolved solely in highly social animals. In contrast to the increasing evidence of MSR in mammals and birds, little is known about MSR in fish.

Laterality is Universal Among Fishes but Increasingly Cryptic Among Derived Groups.

Laterality has been studied in several vertebrates, mainly in terms of brain lateralization and behavioral laterality, but morphological asymmetry has not been extensively investigated. Asymmetry in fishes was first described in scale-eating cichlids from Lake Tanganyika, in the form of bilateral dimorphism in which some individuals, when opening their mouths, twist them to the right and others to the left. This asymmetry has a genetic basis, and is correlated with lateralized attack behaviors.

Facial Recognition in a Discus Fish (Cichlidae): Experimental Approach Using Digital Models.

A number of mammals and birds are known to be capable of visually discriminating between familiar and unfamiliar individuals, depending on facial patterns in some species. Many fish also visually recognize other conspecifics individually, and previous studies report that facial color patterns can be an initial signal for individual recognition. For example, a cichlid fish and a damselfish will use individual-specific color patterns that develop only in the facial area.

The social and ecological costs of an 'over-extended' phenotype.

Extended phenotypes offer a unique opportunity to experimentally manipulate and identify sources of selection acting on traits under natural conditions. The social cichlid fish Neolamprologus multifasciatus builds nests by digging up aquatic snail shells, creating an extended sexual phenotype that is highly amenable to experimental manipulation through addition of extra shells. Here, we find sources of both positive sexual selection and opposing natural selection acting on this trait; augmenting shell nests increases access to mates, but also increases social aggression and predation risk.

Facial Recognition in a Group-Living Cichlid Fish.

The theoretical underpinnings of the mechanisms of sociality, e.g. territoriality, hierarchy, and reciprocity, are based on assumptions of individual recognition.

Depth segregation and diet disparity revealed by stable isotope analyses in sympatric herbivorous cichlids in Lake Tanganyika.

Background: Lake Tanganyika in the African Great Rift Valley is known as a site of adaptive radiation in cichlid fishes. Diverse herbivorous fishes coexist on a rocky littoral of the lake. Herbivorous cichlids have acquired multiple feeding ecomorphs, including grazer, browser, scraper, and scooper, and are segregated by dietary niche.

Diet disparity among sympatric herbivorous cichlids in the same ecomorphs in Lake Tanganyika: amplicon pyrosequences on algal farms and stomach contents.

Background: Lake Tanganyika, an ancient lake in the Great Rift Valley, is famous for the adaptive radiation of cichlids. Five tribes of the Cichlidae family have acquired herbivory, with five ecomorphs: grazers, browsers, scrapers, biters and scoopers. Sixteen species of the herbivorous cichlids coexist on a rocky littoral slope in the lake.

Duration of memory of dominance relationships in a group living cichlid.

Animal contests are costly and tend to escalate when rivals have similar competitive abilities. Individuals that remember dominance relationships with rivals may avoid repeated agonistic interactions and hence avoid the costs of repeated escalation of contests. However, it can be difficult to experimentally disentangle the effects of memory from those of loser effects (losers behaving subordinately due to prior defeats).

Maternal food provisioning in a substrate-brooding African cichlid.

Fish demonstrate the greatest variety of parental care strategies within the animal kingdom. Fish parents seldom provision food for offspring, with some exceptions predominantly found in substrate-brooding Central American cichlids and mouth-brooding African cichlids. Here, we provide the first evidence of food provisioning in a substrate-brooding African cichlid Neolamprologus mondabu.

Territorial males can sire more offspring in nests with smaller doors in the cichlid Lamprologus lemairii.

To examine how territorial males counter reproductive parasites, we examined the paternity of broods guarded by territorial males using 5 microsatellite loci and factors that determine siring success in a wild population of the Lake Tanganyika cichlid Lamprologus lemairii. Females enter rock holes (nests) and spawn inside, and territorial males release milt over the nest openings. Sneakers attempt to dart into the nests, but territorial males often interrupt the attempt.