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In this review, we consider the definitions and experimental approaches to emotional contagion and prosocial behaviour in mammals and explore their evolutionary conceptualisation for studying their occurrence in the evolutionarily divergent vertebrate group of ray-finned fish. We present evidence for a diverse set of fish phenotypes that meet definitional criteria for prosocial behaviour and emotional contagion and discuss conserved mechanisms that may account for some preserved social capacities in fish. Finally, we provide some considerations on how to address the question of interdependency between emotional contagion and prosocial response, highlighting the importance of recognition processes, decision-making systems, and ecological context for providing evolutionary explanations., Competing Interests: Declaration of Competing Interest The authors declare that they have no competing interests or personal relationships that influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

It is generally agreed that variation in social and/or environmental complexity yields variation in selective pressures on brain anatomy, where more complex brains should yield increased intelligence. While these insights are based on many evolutionary studies, it remains unclear how ecology impacts brain plasticity and subsequently cognitive performance within a species. Here, we show that in wild cleaner fish (Labroides dimidiatus), forebrain size of high-performing individuals tested in an ephemeral reward task covaried positively with cleaner density, while cerebellum size covaried negatively with cleaner density. This unexpected relationship may be explained if we consider that performance in this task reflects the decision rules that individuals use in nature rather than learning abilities: cleaners with relatively larger forebrains used decision-rules that appeared to be locally optimal. Thus, social competence seems to be a suitable proxy of intelligence to understand individual differences under natural conditions.

Distinct patterns of gene expression often underlie intra- and intersexual differences, and the study of this set of coregulated genes is essential to understand the emergence of complex behavioural phenotypes. Here, we describe the development of a de novo transcriptome and brain gene expression profiles of wild-caught peacock blenny, Salaria pavo, an intertidal fish with sex-role reversal in courtship behaviour (i.e., females are the courting sex) and sequential alternative reproductive tactics in males (i.e., larger and older nest-holder males and smaller and younger sneaker males occur). Sneakers mimic both female's courtship behaviour and nuptial coloration to get access to nests and sneak fertilizations, and later in life transition into nest-holder males. Thus, this species offers the unique opportunity to study how the regulation of gene expression can contribute to intersex phenotypes and to the sequential expression of male and female behavioural phenotypes by the same individual. We found that at the whole brain level, expression of the sneaker tactic was paralleled by broader and divergent gene expression when compared to either females or nest-holder males, which were more similar between themselves. When looking at sex-biased transcripts, sneaker males are intersex rather than being either nest-holder or female-like, and their transcriptome is simultaneously demasculinized for nest-holder-biased transcripts and feminized for female-biased transcripts. These results indicate that evolutionary changes in reproductive plasticity can be achieved through regulation of gene expression, and in particular by varying the magnitude of expression of sex-biased genes, throughout the lifetime of the same individual., (© 2017 John Wiley & Sons Ltd.)

There is strong evidence that brain nonapeptides are implicated as modulators of a wide array of social and reproductive behaviors in fishes. However, the question remains, as to whether there is a link between the distribution of active nonapeptides across brain regions and fishes specific behavioral phenotypes. To explore this link we compared the nonapeptides' profile across the brains of fishes representing different degrees of mutualistic behavior (here: cleaning behavior). Herein we studied the quantitative distribution of both nonapeptides, arginine vasotocin (AVT) and isotocin (IT), in the brains of four species of fish belonging to the family Labridae: two are obligatory cleaners throughout their entire life (Labroides dimidiatus and Labroides bicolor), one species is a facultative cleaner (Labropsis australis; juveniles are cleaners and adults are corallivorous), and one is a non-cleaner species, corallivorous throughout its entire life (Labrichthys unilineatus). The biologically available AVT and IT concentrations were measured simultaneously in distinct brain macro-areas: forebrain, optic tectum, cerebellum and brain stem, using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We showed that the levels of both AVT and IT varied significantly across species, as measured in the whole brain or in the specific macro-areas. Significantly higher AVT concentrations in the cerebellum which were found in the obligate cleaners seemed to be related to expression of mutualistic behavior. On the other hand, the higher levels of brain IT in the non-cleaner L. unilineatus suggested that these might be linked to the development of sexual dimorphism, which occurs only in this non-cleaner species., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The mechanisms regulating sexual behaviours in female vertebrates are still poorly understood, mainly because in most species sexual displays in females are more subtle and less frequent than displays in males. In a sex-role reversed population of a teleost fish, the peacock blenny Salaria pavo, an external fertilizer, females are the courting sex and their sexual displays are conspicuous and unambiguous. We took advantage of this to investigate the role of ovarian-synthesized hormones in the induction of sexual displays in females. In particular, the effects of the sex steroids oestradiol (E2) and testosterone (T) and of the prostaglandin F2α (PGF2α) were tested. Females were ovariectomized and their sexual behaviour tested 7 days (sex steroids and PGF2α) and 14 days (sex steroids) after ovariectomy by presenting females to an established nesting male. Ovariectomy reduced the expression of sexual behaviours, although a significant proportion of females still courted the male 14 days after the ovary removal. Administration of PGF2α to ovariectomized females recovered the frequency of approaches to the male's nest and of courtship displays towards the nesting male. However, E2 also had a positive effect on sexual behaviour, particularly on the frequency of approaches to the male's nest. T administration failed to recover sexual behaviours in ovariectomized females. These results suggest that the increase in E2 levels postulated to occur during the breeding season facilitates female mate-searching and assessment behaviours, whereas PGF2α acts as a short-latency endogenous signal informing the brain that oocytes are mature and ready to be spawned. In the light of these results, the classical view for female fishes, that sex steroids maintain sexual behaviour in internal fertilizers and that prostaglandins activate spawning behaviours in external fertilizers, needs to be reviewed.

Phenotypic change in response to variation in environmental cues has been widely documented in fish. Transitions in social dominance, in particular, have been shown to induce a rapid switch in reproductive phenotypes in many species. However, this effect has been mainly studied in adults and focused on behavioural transitions. The way social cues constraint the phenotypic development of juveniles remains poorly studied in fish. We tested the importance of social dominance and density in the phenotypic development of juveniles of the peacock blenny Salaria pavo. This species shows sequential male alternative reproductive tactics. In the first breeding season males can reproduce as nest-holders or as parasitic males (female-mimicking), or postpone reproduction; from the following season afterwards all males reproduce as nest-holders. Parasitic males have relatively larger testes that lack a testicular gland, present in the testes of nest-holders. The testicular gland is the main source of androgens in the testes and accordingly nest-holders have higher circulating androgen levels. In addition, exogenous androgen administration to parasitic males promotes the development of secondary sexual characters (SSC) only present in nest-holders such as a head crest and an anal gland. We raised juveniles under a high or low-density treatment and monitored social interactions for 1 month. No significant effect of density on the development of juvenile males was detected. However, within each replicate, the relative body size of juvenile males at the beginning of the experiment determined their dominance status, with dominant males developing towards the nest-holder morphotype. Dominant males engaged in more nest defence behaviour, showed larger testicular glands, had higher levels of 11-ketotestosterone (11-KT) and testosterone (T) and developed more SSC, as compared to subordinate males. However, these effects of social dominance were moderated by body condition as only dominant males in good body condition developed SSC. The effect of social dominance and of the area of the testicular gland on the development of SSC was mediated by 11-KT and on the expression of nest defence behaviour by T. Interestingly, in spite of the higher androgen levels and more pronounced morphologic development of SSC in dominant individuals, gonadal development was independent of social dominance and most fish still had underdeveloped testis at the end of the experiment. In conclusion, social dominance promoted the development of the testicular gland, an increase in circulating androgen levels and the development of SSC, but did not promote testicular development. This suggests a dissociation of mechanisms underlying sexual maturation and the expression of male reproductive traits. This dissociation seems to be the key for the occurrence of female-mimicking males in this species, which are sexually mature despite lacking the SSC typical of nest-holders., (Copyright © 2012 Elsevier Inc. All rights reserved.)

social stressors typically elicit two distinct behavioural responses in vertebrates: an active response (i.e., "fight or flight") or behavioural inhibition (i.e., freezing). Here, we report an interesting exception to this dichotomy in a Caribbean cleaner fish, which interacts with a wide variety of reef fish clients, including predatory species. Cleaning gobies appraise predatory clients as potential threat and become stressed in their presence, as evidenced by their higher cortisol levels when exposed to predatory rather than to non-predatory clients. Nevertheless, cleaning gobies neither flee nor freeze in response to dangerous clients but instead approach predators faster (both in captivity and in the wild), and interact longer with these clients than with non-predatory clients (in the wild). We hypothesise that cleaners interrupt the potentially harmful physiological consequences elicited by predatory clients by becoming increasingly proactive and by reducing the time elapsed between client approach and the start of the interaction process. The activation of a stress response may therefore also be responsible for the longer cleaning service provided by these cleaners to predatory clients in the wild. Future experimental studies may reveal similar patterns in other social vertebrate species when, for instance, individuals approach an opponent for reconciliation after a conflict.

Blenniid fish exhibit a polygynandric mating system with parental care restricted to males. Nest-holder males defend a breeding territory centered on their nest, usually a crevice or hole in a rocky substrate, to which they attract females to spawn. Females, on the other hand, must search for nests in order to spawn and usually are the choosy sex, producing several sequential egg batches and broods during the breeding season. Therefore, male blennies are more site-attached than females. This situation offers an opportunity to investigate potential neural correlates of intraspecific differences in selective pressures for different spatial abilities in these species. Since the dorsolateral telencephalon has been considered a teleost homologue of the mammalian hippocampus, we predicted that the spatial abilities required for females to locate and return accurately to nests of males may have produced a sex difference in the size of the telencephalic nuclei involved in spatial abilities, biased towards females. To test this hypothesis, we assessed the home ranges and measured the size of the dorsolateral telencephalon of both sexes during the breeding season in two blenniid species, the shanny (Lipophrys pholis) and the Azorean rock-pool blenny (Parablennius parvicornis). We chose these two species because they differ in the degree of chemical communication they use, and this could also lead to differences in telencephalic areas. As predicted, in both species females present considerably larger home ranges paralleled by larger dorsolateral ventral telencephalic nuclei (DLv) than males. Other telencephalic nuclei that were measured did not show any sex difference in size. These results suggest that the DLv is involved in spatial abilities in blenniid fish and that sexual selection may be promoting this divergence as already described for mammals and birds., (Copyright © 2011 S. Karger AG, Basel.)

Interactions between the bluestreak cleaner wrasse Labroides dimidiatus and its client reef fish are a textbook example of interspecific mutualism. The fact that clients actively visit cleaners and invite inspection, together with evidence that cleaners eat many client ectoparasites per day, indeed strongly suggests a mutualistic relationship. What remains unknown is how parasite removal affects the physiology of clients and thereby their body condition, health, and immune function. Here we addressed these issues in a field study in Ras Mohammed National Park, Egypt. In our study area, small reef patches are inter-spaced with areas of sandy substrate, thereby preventing many species (i.e., residents, including cleaner wrasses) from travelling between the reef patches. This habitat structure leads to a mosaic of resident clients with and without access to bluestreak cleaner wrasses, further referred to as "cleaner access", on which we focused our study. We found that residents with cleaner access had higher body condition than residents without cleaner access. However, indicators of stress like variation in cortisol levels corrected for handling time and various immune parameters were apparently unaffected by cleaner access. In fact antibody responses were significantly higher in fishes without cleaner access. This suggests that cleaner access decreases the need for active immunity and that this releases resources that might be allocated to other functions such as somatic growth and reproduction., (Copyright © 2010 Elsevier Inc. All rights reserved.)

We tested whether subordinate helper males of the Lake Tanganyika cooperatively breeding cichlid Neolamprologus pulcher show elevated excretion levels of the stress hormone cortisol and reduced levels of 11-ketotestosterone and testosterone when living in groups with a small breeder male, compared to similar helper males living in groups with a large breeder male, in a full-factorial repeated measures experimental design. We also measured the same hormones in breeder males with and without helper males. Previous research showed that the size difference between large male helpers and male breeders in groups of this species influences behaviour and growth decisions. Contrary to our expectation, no effect of the size-difference between helper males and breeder males on helper hormone levels was detected. Furthermore, helper males had similar hormone excretion levels to those of size-matched breeder males without helpers, and to small breeder males. There was no influence of egg laying on breeder male and helper hormone levels during the experiment. Interestingly, all three hormone levels were significantly lower in helpers showing elevated levels of submissive behaviour towards the breeders, independently of the size of the breeder males. The low cortisol levels suggest that helper males can successfully reduce stress by appeasing breeder males through submission. Furthermore, helper males showing a high level of submissive behaviour had lower levels of androgens than less submissive helpers, suggesting a lower reproductive potential in submissive helpers. We propose that helper submission may be used as an honest signal of reduced interest in reproduction towards the breeder male in this species.

The occurrence of intra-sexual variation in reproduction is a widespread phenomenon in teleosts. One such form of variation consists in the occurrence of alternative male types: males that invest resources in mate attraction and males that exploit the investment of the former males, by trying to sneak fertilizations during spawning. These alternative reproductive tactics can be classified according to their plasticity during the life span of the individuals (i.e., fixed vs. sequential vs. reversible). Furthermore, the differences between morphs within a given species may involve a set of different traits, including reproductive behavior, the differentiation of male morphological traits, and the patterns of gonad tissue allocation and the differentiation of gonadal accessory glands. In this paper, we review the available data on four species exhibiting different types of intra-sexual plasticity in reproduction that have been studied in our lab. The data on the proximate mechanisms, androgens and forebrain arginine-vasotocin (AVT), underlying these alternative tactics suggest that between-morph differences in androgen levels, especially in 11-ketotestosterone, are especially present in species where the alternative male types have evolved morphological traits that are tactic-specific (i.e., sexual polymorphisms) and that differences in AVT appear to be related to between-morph differences in the expression of courtship behavior. Therefore, this comparative approach leads us to propose that the different endocrine systems are involved in the differentiation of different sets of traits that make up alternative phenotypes, and that the differentiation of alternative tactics is not controlled by a single endocrine system (e.g., androgens).

In the common Azorean rock-pool blenny, Parablennius parvicornis, males exhibit alternative reproductive morphologies: (1) larger males defend nest sites, provide parental care, have anal glands (involved in pheromone release), testicular glands, and low gonad:body weight ratio (GSI) and (2) smaller, younger, males do not defend nests, have reduced glands and high GSI. These smaller non-nesting males behave as satellites (associated with nests) or sneakers (moving among nests), attempting to achieve parasitic fertilizations via sperm competition. In non-mammals, arginine vasotocin (AVT) is a key hypothalamic peptide involved in the control of reproductive behavior and physiology, and several fish species that exhibit alternative male reproductive morphs show polymorphism in AVT brain chemistry. We conducted an immunocytochemical study to generate comparative data on this intertidal blenny. Our analysis showed no difference in AVT-immunoreactive cell number or size between the male morphs, which is consistent with studies on other fish, including blennies. The number of AVT cells was positively correlated to fish body mass, while cell size showed no such relation. If corrected for body mass, the smaller non-nesting males have significantly more cells than the large nesting males. Our data suggest that the size and number of forebrain AVT cells develops initially to allow for reproduction in the young non-nesting males and this pattern does not appear to change when males take on the nesting morphotype later in life. This result appears to be consistent in many fishes with alternative male morphotypes.

In this paper, we present the results of cellular and molecular studies on the neuroendocrine correlates of male sexual polymorphism in a population of the blenniid fish Salaria pavo (Risso). Bigger and older males defend nests, whereas smaller and younger males mimic female nuptial coloration and behavior to gain access to nests and sneak fertilizations. In this population, sex-role reversal in courtship also occurs (i.e., females are the courting sex). Immunocytochemistry and in situ hybridization were used to examine the production of arginine vasotocin (AVT) peptide and messenger RNA, respectively. The expression of AVT mRNA on a per-cell basis was correlated with mating behavior, rather than with sex morphotype, which suggests that the greater level of AVT mRNA expression in females and sneakers is correlated with the production of courtship behavior. On the other hand, the number and size of AVT peptide-producing cells in both male types is higher or larger, respectively, than in females, which suggests that it is correlated with sex morphotype, rather than with mating behavior.

In many territorial species androgen hormones are known to increase in response to territorial intrusions as a way to adjust the expression of androgen-dependent behaviour to social challenges. The dear enemy effect has also been described in territorial species and posits that resident individuals show a more aggressive response to intrusions by strangers than by other territorial neighbours. Therefore, we hypothesized that the dear enemy effect may also modulate the androgen response to a territorial intrusion. Here we tested this hypothesis in male cichlid fish (Mozambique tilapia, Oreochromis mossambicus) using a paradigm of four repeated territorial intrusions, either by the same neighbour or by four different unfamiliar intruders. Neighbour intruders elicited lower aggression and a weaker androgen response than strangers on the first intrusion of the experiment. With repeated intrusions, the agonistic behaviour of the resident males against familiar intruders was similar to that displayed towards strangers. By the fourth intrusion the androgen response was significantly reduced and there was no longer a difference between the responses to the two types of intruders. These results suggest that the dear enemy effect modulates the androgen response to territorial intrusions and that repeated intrusions lead to a habituation of the androgen response. [ABSTRACT FROM AUTHOR]

Animals communicate through the exchange of signals. However, third-party individuals can detect and intercept signals not directly sent to them, a phenomenon known as eavesdropping, and the presence of bystanders can influence the signalling behaviour of interacting conspecifics, a phenomenon named the audience effect. So far, research done on audience effects and eavesdropping has been mainly focused on their function, rather than on their proximate mechanisms. For this reason, we were interested in testing the occurrence of audience effects on male zebrafish, a genetically tractable model organism that is emerging as a major candidate for the study of the neural basis of social behaviour. Here, pairs of males were exposed to a mixed-sex shoal, which was used as an audience, at two different times: (1) during a contest between them, to test for an audience effect and (2) before the contest, to test whether this prior exposure influences subsequent agonistic behaviour (i.e. aggressive priming). We analysed the pairs' aggressive signalling during the contest by measuring variables that characterize both the individuals' behaviour and the interaction, and found that pre-exposure to an audience induced a shorter latency to display, an increase in the time dominants spent chasing subordinates and a shorter time to resolve the agonistic interaction. Also, exposure to the audience during the interaction led to a higher number of interactions in which displays occurred, a higher number of resolved interactions with displays and a decrease in the escalation of aggression for resolved interactions. These results add zebrafish to the literature on the audience effect and, most importantly, open the way for the study of the neural mechanisms involved in the processing of social information in a model organism. [ABSTRACT FROM AUTHOR]

The nonapeptide arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin play a key role in the regulation of social behaviour across vertebrates. In teleost fishes, three AVT neuronal populations have been described in the preoptic area (POA): the parvocellular (pPOA), the magnocellular (mPOA) and the gigantocellular (gPOA). Neurons from each of these areas project both to the pituitary and to other brain regions, where AVT is supposed to regulate neural circuits underlying social behaviour. However, in the fish species studied so far, there is considerable variation in which AVT neuronal populations are involved in behavioural modulation and in the direction of the effect. In this study, the association between AVT neuronal phenotypes and social status was investigated in the Mozambique tilapia (Oreochromis mossambicus). This species is an African female mouth-brooding cichlid fish in which males form breeding aggregations in which dominant males establish territories and subordinate males to act as floaters. With respect to sex differences in AVT neuronal phenotypes, females have a larger number of AVT neurons in the pPOA and mPOA. Within males, AVT appeared associated with social subordination, as indicated by the larger cell body areas of AVT neurons in mPOA and gPOA nuclei of non-territorial males. There were also positive correlations between submissive behaviour and the soma size of AVT cells in all three nuclei and AVT cell number in the mPOA. In summary, the results provide evidence for an involvement of AVT in the modulation of social behaviour in tilapia, but it was not possible to identify specific roles for specific AVT neuronal populations. The results presented here also contrast with those previously published for another cichlid species with a similar mating system, which highlights the species-specific nature of the pattern of association between AVT and social behaviour even within the same taxonomic family. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Background: Social plasticity is a pervasive feature of animal behavior. Animals adjust the expression of their social behavior to the daily changes in social life and to transitions between life-history stages, and this ability has an impact in their Darwinian fitness. This behavioral plasticity may be achieved either by rewiring or by biochemically switching nodes of the neural network underlying social behavior in response to perceived social information. Independent of the proximate mechanisms, at the neuromolecular level social plasticity relies on the regulation of gene expression, such that different neurogenomic states emerge in response to different social stimuli and the switches between states are orchestrated by signaling pathways that interface the social environment and the genotype. Here, we test this hypothesis by characterizing the changes in the brain profile of gene expression in response to social odors in the Mozambique Tilapia, Oreochromis mossambicus. This species has a rich repertoire of social behaviors during which both visual and chemical information are conveyed to conspecifics. Specifically, dominant males increase their urination frequency during agonist encounters and during courtship to convey chemical information reflecting their dominance status. Results: We recorded electro-olfactograms to test the extent to which the olfactory epithelium can discriminate between olfactory information from dominant and subordinate males as well as from pre- and post-spawning females. We then performed a genome-scale gene expression analysis of the olfactory bulb and the olfactory cortex homolog in order to identify the neuromolecular systems involved in processing these social stimuli. Conclusions: Our results show that different olfactory stimuli from conspecifics' have a major impact in the brain transcriptome, with different chemical social cues eliciting specific patterns of gene expression in the brain. These results confirm the role of rapid changes in gene expression in the brain as a genomic mechanism underlying behavioral plasticity and reinforce the idea of an extensive transcriptional plasticity of cichlid genomes, especially in response to rapid changes in their social environment. [ABSTRACT FROM AUTHOR]

In the peacock blenny (Salaria pavo) the reproductive behaviour is described to vary between two populations that differ in nest availability. At the Gulf of Trieste (GT), Italy, where nest availability is high, conventional sex roles are present and males adopting an alternative parasitic reproductive tactic are rare. Conversely, at Ria Formosa (RF), Portugal, where nest site availability is low, females are the courting sex and a high percentage of parasitic males occur. Laboratory experiments were used to study the degree of plasticity of the reproductive behaviours used by females and by the two male morphs in both populations. Nesting males were sequentially presented with a female and a female-like parasitic male and the reproductive behaviours of all fish were quantified. Under similar laboratory conditions, nesting males from both populations did not differ in sexual or agonistic displays towards females or parasitic males, showing that males from the sex-reversed population are also able to express significant levels of courtship. In contrast, females followed the typical population pattern, with females from RF courting nesting males more and more readily than females from GT. We hypothesised that apparent differences in behavioural plasticity between nesting males and females were a consequence of the perception of the presence of eggs in the nest. Nesting males from both populations received an empty nest during test trials and, thus, had to court females in order to receive a first spawn. On the other hand, females were probably unaware of the presence or absence of eggs when presented to the nesting male and assumed the population typical courtship profile. Interestingly, the parasitic males' behaviour towards the nesting male closely followed the displays of females from their own population; parasitic males from RF courted the nesting male with a high frequency of female-like displays while parasitic males from GT failed to exhibit female-like courtship behaviour. Taken together, the results suggest that S. pavo presents high levels of plasticity in reproductive behaviours and that these may underlie the interpopulation differences in behaviour reported for the species. Additionally, the results also suggest that the parasitic male reproductive tactic at GT is not based on female-mimicry. [ABSTRACT FROM AUTHOR]

The ability to respond to stress is vital to the survival of any living organism, though sustained reactions can become detrimental to the health and welfare of animals. Stress responses of vertebrates are known through several studies in their physiological, behavioural and psychological components, under acute and chronic contexts. In fish, the physiological and behavioural aspects of stress are considerably well known phenomena and show striking similarities to those of other vertebrates. However, the psychological component is not well known. Some authors deny mental experiences to fish on the basis of their lack of neocortex. Nevertheless, recent studies have shown neuroendocrine, cognitive and emotional processes in fish that are not only equivalent to other vertebrates, but also allow inferring some forms of mental representation. The integration of psychological elements in fish stress physiology is insufficiently studied, but, as discussed in this article, there is already indirect evidence to admit that some form of stimuli appraisal can take place in fish. This fact has profound implications on the regulation of the stress response, as well as on fish welfare and its management. [ABSTRACT FROM AUTHOR]

Androgens are classically thought of as the sex steroids controlling male reproduction. However, in recent years evidence has accumulated showing that androgens can also be affected by the interactions between conspecifics, suggesting reciprocal interactions between androgens and behaviour. These results have been interpreted as an adaptation for individuals to adjust their agonistic motivation and to cope with changes in their social environment. Thus, male–male interactions would stimulate the production of androgens, and the levels of androgens would be a function of the stability of its social environment [‘challenge hypothesis’, Gen. Comp. Endocrinol. 56 (1984) 417]. Here the available data on social modulation of androgen levels in male teleosts are reviewed and some predictions of the challenge hypothesis are addressed using teleosts as a study model. We investigate the causal link between social status, territoriality and elevated androgen levels and the available evidence suggests that the social environment indeed modulates the endocrine axis of teleosts. The association between higher androgen levels and social rank emerges mainly in periods of social instability. As reported in the avian literature, in teleosts the trade-off between androgens and parental care is indicated by the fact that during the parental phase breeding males decreased their androgen levels. A comparison of androgen responsiveness between teleost species with different mating and parenting systems also reveals that parenting explains the variation observed in androgen responsiveness to a higher degree than the mating strategy. Finally, the adaptive value of social modulation of androgens and some of its evolutionary consequences are discussed. [Copyright &y& Elsevier]

Presents a study on visual communication in a marine fish, Salaria pavo, using video recordings. Design of the video monitors; Controversy in using video playbacks in the study of animal visual communication; Details on the reactions to the stimulus of the Salaria pavo species; Discussion on reaction differences of species.

Describes a method for recording the coordinates of a fish in an aquarium in a three-dimensional space using a single video camera and a mirror. Review of related literature; Assumptions of the lens formula.

Group living animals may eavesdrop on signalling interactions between conspecifics in order to collect adaptively relevant information obtained from others, without incurring in the costs of first-hand information acquisition. This ability (aka social eavesdropping) is expected to impact Darwinian fitness, and hence predicts the evolution of cognitive processes that enable social animals to use public information available in the environment. These adaptive specializations in cognition may have evolved both at the level of learning and memory mechanisms, and at the level of input mechanisms, such as attention, which select the information that is available for learning. Here we used zebrafish to test if attention in a social species is tuned to the exchange of information between conspecifics. Our results show that zebrafish are more attentive towards interacting (i.e. fighting) than towards non-interacting pairs of conspecifics, with the exposure to fighting not increasing activity or stress levels. Moreover, using video playbacks to manipulate form features of the fighting fish, we show that during the assessment phase of the fight, bystanders' attention is more driven by form features of the interacting opponents; whereas during the post-resolution phase, it is driven by biological movement features of the dominant fish chasing the subordinate fish. [ABSTRACT FROM AUTHOR]

Photoperiod is a major environmental cue that signals breeding conditions in animals living in temperate climates. Therefore, the activity of the reproductive (i.e. hypothalamic–pituitary–gonadal, HPG) axis and of the expression of reproductive behaviors, including territoriality, is responsive to changes in day length. However, at low latitudes the seasonal variation in day length decreases dramatically and photoperiod becomes less reliable as a breeding entraining cue in tropical species. In spite of this, some tropical mammals and birds have been found to still respond to small amplitude changes in photoperiod (e.g. 17 min). Here we tested the effect of 2 photoperiod regimes, referred to as long-day (LD: 16L:08D) and short-day (SD: 08L:16D), on the activity of the HPG axis, on aggressive behavior and in the androgen response to social challenges in males of the tropical cichlid fish Tilapia rendalli . For each treatment, fish were transferred from a pre-treatment photoperiod of 12L:12D to their treatment photoperiod (either LD or SD) in which they were kept for 20 days on stock tanks. Afterwards, males were isolated for 4 days in glass aquaria in order to establish territories and initial androgen levels (testosterone, T; 11-ketotestosterone, KT) were assessed. On the 4th day, territorial intrusions were promoted such that 1/3 of the isolated males acted as residents and another 1/3 as intruders. Territorial intrusions lasted for 1 h to test the effects of a social challenge under different photoperiod regimes. Photoperiod treatment (either SD or LD) failed to induce significant changes in the HPG activity, as measured by androgen levels and gonadosomatic index. However, SD increased the intensity of aggressive behaviors and shortened the time to settle a dominance hierarchy in an androgen-independent manner. The androgen responsiveness to the simulated territorial intrusion was only present in KT but not for T. The percent change in KT levels in response to the social challenge was different between treatments (SD > LD) and between male types (resident > intruder). The higher androgen response to a social challenge in residents under SD may be explained by the time course of the androgen response that due to the long time it takes to fight resolution under LD, might have been delayed. This result illustrates the importance of incorporating time response data in social endocrinology studies. [ABSTRACT FROM AUTHOR]

Gonads are the main source of sex steroids, which have been implicated in the regulation of sexually differentiated behavior, such as reproductive and aggressive displays. In the Mozambique tilapia ( Oreochromis mossambicus ) territorial males have higher androgen levels than non-territorials, express reproductive behavior and use a urine-borne pheromone to signal their social status towards conspecifics. Here we investigated the effects of gonadectomy on the circulating levels of androgens and cortisol, and on the expression of aggressive and reproductive behavior (nest building, courtship behavior, and nuptial coloration). Males were either castrated, urine bladder damaged, or sham-operated and visually exposed to a group of females during 8 consecutive days and subsequently to a male on day 9. The urine bladder damaged treatment was included in the experimental design because a full castration procedure in this species causes quite often damage to the urine bladder. Gonadectomy lowers dramatically the circulating levels of androgens measured at 4 and 8 days post-castration and abolishes the expression of nest building, courtship behavior and nuptial coloration, but has no effect on the expression of aggressive behavior. These results confirm the gonads as the main source of androgens in this species and show that androgens are necessary for the expression of reproductive behaviors. However, the expression of aggressive behavior seems to be decoupled from gonadal steroids, namely androgens, suggesting the action of independent central mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: In recent years there has been an increasing interest in the cognitive abilities of fish with implications for animal welfare and management of rearing operations. Although it is known that psychological factors can modulate the stress response in mammals, this aspect has seldom been investigated within stress in fish. In this study we investigate whether the perception (appraisal) that fish make of significant environmental events modifies their behavioural and physiological response. For this purpose we have used a predictable vs. unpredictable paradigm for positive (feeding) and negative (confinement) events using the cichlid fish Oreochromis mossambicus as a model species. Results show that there is a differential effect of predictability for the feeding and confinement events. In the confinement experiment, predictability involved more attention to the visual cue and lower cortisol. The feeding event triggered higher levels of anticipatory behaviour and a tendency for higher cortisol in the predictable group. Therefore, predictable negative events reduce the cortisol response. Predictable positive events may elicit an anticipatory response, and when there is a significant delay between the visual cue and the actual occurrence of the event, it may also contain elements that can be interpreted as a stress response. These findings demonstrate that fish can appraise relevant aspects of the environment, with welfare implications for housing, husbandry and experimental procedures. [ABSTRACT FROM AUTHOR]

Abstract: Recent behavioural, cognitive and neurophysiological studies strongly suggest that fish are capable of psychological experiences. Therefore, identifying needs from the animals’ point of view is likely to be one of the best approaches to understand their welfare. Motivational tests, as a measure of what animals want, have been developed and refined for some decades. Despite numerous studies on fish motivational systems, none have attempted to quantify their motivation using this approach. Motivation studies often imply operant tasks for which various devices are used. The aim of this study was to adapt a push-door to quantify motivation in a cichlid fish, the Mozambique tilapia (Oreochromis mossambicus). Males of this species have strong snouts which they use for a number of activities and are thus suited to push. Twelve males of different social status were tested for three kinds of reinforcers: food, social partner and a control (additional space with substrate only). The animals were required to work the door (push/touch) at an ascending cost in order to have access to the resources. Measures of motivation included latency to open the door, work attention and maximum price paid. Latency to open the door increased with increasing cost for all resources, with the highest latency for the control reinforcer. Work attention was constant with increasing costs for social partners and food, and higher than the control. Work attention decreased for the control as cost increased. Maximum price paid was consistent with these results, being higher for social partners and food than for the control. The results of the three measures were consistent with each other and showed that the push-door can be used to measure motivation in this species. Further refinement of the present experimental set up will allow the use of this paradigm in the future, in order to improve knowledge on how this species values and ranks its needs. [ABSTRACT FROM AUTHOR]

Proper response to stress and social stimuli depends on orchestrated development of hypothalamic neuronal circuits. Here we address the effects of the developmental transcription factor orthopedia (Otp) on hypothalamic development and function. We show that developmental mutations in the zebrafish paralogous gene otpa but not otpb affect both stress response and social preference. These behavioral phenotypes were associated with developmental alterations in oxytocinergic (OXT) neurons. Thus, otpa and otpb differentially regulate neuropeptide switching in a newly identified subset of OXT neurons that co-express the corticotropin-releasing hormone (CRH). Single-cell analysis revealed that these neurons project mostly to the hindbrain and spinal cord. Ablation of this neuronal subset specifically reduced adult social preference without affecting stress behavior, thereby uncoupling the contribution of a specific OXT cluster to social behavior from the general otpa-/- deficits. Our findings reveal a new role for Otp in controlling developmental neuropeptide balance in a discrete OXT circuit whose disrupted development affects social behavior. [ABSTRACT FROM AUTHOR]

The teleost fish nonapeptides, arginine vasotocin (AVT) and isotocin (IT), have been implicated in the regulation of social behavior. These peptides are expected to be involved in acute and transient changes in social context, in order to be efficient in modulating the expression of social behavior according to changes in the social environment. Here we tested the hypothesis that short-term social interactions are related to changes in the level of both nonapeptides across different brain regions. For this purpose we exposed male zebrafish to two types of social interactions: (1) real opponent interactions, from which a Winner and a Loser emerged; and (2) mirror-elicited interactions, that produced individuals that did not experience a change in social status despite expressing similar levels of aggressive behavior to those of participants in real-opponent fights. Non-interacting individuals were used as a reference group. Each social phenotype (i.e. Winners, Losers, Mirror-fighters) presented a specific brain profile of nonapeptides when compared to the reference group. Moreover, the comparison between the different social phenotypes allowed to address the specific aspects of the interaction (e.g. assessment of opponent aggressive behavior vs. self-assessment of expressed aggressive behavior) that are linked with neuropeptide responses. Overall, agonistic interactions seem to be more associated with the changes in brain AVT than IT, which highlights the preferential role of AVT in the regulation of aggressive behavior already described for other species. [ABSTRACT FROM AUTHOR]