Intermale competition in sexually mature arctic charr: effects on brain monoamines, endocrine stress responses, sex hormone levels, and behavior

Behavioural, developmental and biochemical effects in zebrafish caused by ibuprofen, irgarol and terbuthylazine

The increasing use of chemicals and their release into aquatic ecosystems are harming aquatic biota. Despite extensive ecotoxicological research, many environmental pollutants' ecological effects are still unknown. This study examined the spatial avoidance, behavioural and biochemical impacts of ibuprofen, irgarol, and terbuthylazine on the early life stages of zebrafish (Danio rerio) under a range of ecologically relevant concentrations (0-500 μg/L). Embryos were exposed following the OECD guideline "fish embryo toxicity test" complemented with biochemical assessment of AChE activity and behavioural analyses (swimming activity) using the video tracking system Zebrabox. Moreover, spatial avoidance was assessed by exposing 120 hpf-old larvae of D. rerio to a gradient of each chemical, by using the heterogeneous multi-habitat assay system (HeMHAS). The results obtained revealed that the 3 compounds delayed hatching at concentrations of 50 and 500 μg/L for both ibuprofen and irgarol and 500 μg/L for terbuthylazine. Moreover, all chemicals elicited a dose-dependent depression of movement (swimming distance) with LOEC values of 5, 500 and 50 μg/L for ibuprofen, irgarol and terbuthylazine, respectively. Zebrafish larvae avoided the three chemicals studied, with 4 h-AC50 values for ibuprofen, irgarol, and terbuthylazine of 64.32, 79.86, and 131.04 μg/L, respectively. The results of the HeMHAS assay suggest that larvae may early on avoid (just after 4 h of exposure) concentrations of the three chemicals that may later induce, apical and biochemical effects. Findings from this study make clear some advantages of using HeMHAS in ecotoxicology as it is: ecologically relevant (by simulating a chemically heterogeneous environmental scenario), sensitive (the perception of chemicals and the avoidance can occur at concentrations lower than those producing lethal or sublethal effects) and more humane and refined approach (organisms are not mandatorily exposed to concentrations that can produce individual toxicity).

Stressful Daylight: Differences in Diel Rhythmicity Between Albino and Pigmented Fish

In laboratory experiments, variously colored strains of animals, including those with albino phenotypes, are commonly used. The melanocortin theory suggests, however, that coloration phenotypes alter animal physiology and behavior. Animals with the albino phenotype show photoreceptor degradation associated with lowered visual accuracy, escape reactions, etc., presumably accompanied by prevailing nocturnal activity and lowered aggressiveness. This assumption was tested in small groups of albino and pigmented European catfish, Silurus glanis, during the diel cycle. The frequency of agonistic interactions was observed during mutual contests for shelters, and subsequently, blood plasma, brain, gill, and liver samples were collected to evaluate stress parameters. In an experimental arena with shelters, the light/dark rhythmicity of locomotor activity and aggressiveness of the two phenotypes were comparable; the peak was observed at night, and a lower peak was observed at dawn. In an experimental stream without shelters, the peak of locomotor activity occurred at night for only the pigmented phenotype. In the evaluation of 4 antioxidants and 1 oxidative stress indicator, representing a total of 15 indices, albino fish showed significant rhythmicity for 8 indices, whereas pigmented catfish showed significant rhythmicity for 5 indices. The production of blood stress parameters with the peak during the day occurred only in albino fish. A complex model was fitted with the aim of evaluating the links between behavioral and biochemical indices. Time periodicity was modeled using a sine wave and confirmed parallel courses of agonistic interactions in the catfish groups; the peak at dawn was associated with a 4.08-fold (conf. int. 3.53–4.7) increase in such interactions. The changes in glucose and superoxide dismutase concentrations varied with phenotype, while the effects of cortisol, lactate and catalase did not. In summary, the rhythmicity of locomotor activity and changes in the aggressiveness of catfish were influenced by shelter availability, and the effect of light-induced stress was more apparent in albino fish than in pigmented conspecific fish. The results suggested that laboratory-raised animals with pigmentation patterns naturally occurring in the wild show more reasonable values during experiments than those with an albino phenotype.

Endoplasmic reticulum stress as a key mechanism in stunted growth of seawater rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Rainbow trout (Oncorhynchus mykiss) is a salmonid species with a complex life-history. Wild populations are naturally divided into freshwater residents and sea-run migrants. Migrants undergo an energy-demanding adaptation for life in seawater, known as smoltification, while freshwater residents display these changes in an attenuated magnitude and rate. Despite this, in seawater rainbow trout farming all fish are transferred to seawater. Under these circumstances, weeks after seawater transfer, a significant portion of the fish die (around 10%) or experience growth stunting (GS; around 10%), which represents an important profitability and welfare issue. The underlying causes leading to GS in seawater-transferred rainbow trout remain unknown. In this study, we aimed at characterising the GS phenotype in seawater-transferred rainbow trout using untargeted and targeted approaches. To this end, the liver proteome (LC-MS/MS) and lipidome (LC-MS) of GS and fast-growing phenotypes were profiled to identify molecules and processes that are characteristic of the GS phenotype. Moreover, the transcription, abundance or activity of key proteins and hormones related to osmoregulation (Gill Na+, K + -ATPase activity), growth (plasma IGF-I, and liver igf1, igfbp1b, ghr1 and ctsl) and stress (plasma cortisol) were measured using targeted approaches.

RESULTS

No differences in Gill Na+, K + -ATPase activity and plasma cortisol were detected between the two groups. However, a significant downregulation in plasma IGF-I and liver igf1 transcription pointed at this growth factor as an important pathomechanism for GS. Changes in the liver proteome revealed reactive-oxygen-species-mediated endoplasmic reticulum stress as a key mechanism underlying the GS phenotype. From the lipidomic analysis, key observations include a reduction in triacylglycerols and elevated amounts of cardiolipins, a characteristic lipid class associated with oxidative stress, in GS phenotype.

CONCLUSION

While the triggers to the activation of endoplasmic reticulum stress are still unknown, data from this study point towards a nutritional deficiency as an underlying driver of this phenotype.

Association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti

Agonistic behavior governs the settlement of conflicts among conspecifics for limiting resources. Sex steroids play a critical role in the regulation of agonistic behavior which in turn may produce modulations in hormone titres. In this study we analyzed the association of androgens and estrogens with agonistic behavior in the annual fish Austrolebias reicherti. This native species inhabits temporary ponds that dry out completely during summer, having one of the shortest lifespans among vertebrates. They are highly sexually dimorphic and have a single breeding season during which they reproduce continuously. Here we measured plasma levels of 11-ketotestosterone (11KT) and 17β-estradiol (E₂) in adult males after the resolution of a social conflict and assessed the role of the aromatase conversion of testosterone (T) to E₂ in male aggression. Winners had higher levels of 11KT than losers yet; winner 11KT levels did not differ from those of males not exposed to a social challenge. E₂ levels did not show differences among winners, losers or control males. However, fights under the aromatase inhibitor Fadrozole were overall less aggressive than control fights. Our results suggest an androgen response to losing a conflict and that the conversion of T to E₂ is involved in the regulation of aggressive behavior. Annual fish extreme life history may give new insights on hormone-behavior interactions.

Evidence that Gulf toadfish use pulsatile urea excretion to communicate social status

Gulf toadfish (Opsanus beta), a highly territorial marine teleost species, are believed to communicate through chemicals released across the gill during pulsatile urea excretion. While freshwater teleost and crustacean urinary signals have been shown to relay information about dominance to reduce physical aggression in future encounters, the use of chemical signals to convey social status in marine teleosts is understudied. Behavior and urea excretion patterns were monitored in pairs of male toadfish during an initial agonistic encounter and in a 2^nd encounter where a subset of pairs had their nares blocked to determine how olfaction, and thus chemical communication, play a role in establishing dominance. Anosmic toadfish did not experience increases in aggressive behavior, unlike other species previously studied. However, behavior and the pattern of urea excretion were disrupted in anosmic pairs compared to control pairs. Specifically, control subordinate fish had an increase in their dominance index during the 2^nd encounter, a response that anosmic subordinate fish did not experience suggesting that without the ability to smell, subordinate fish cannot recognize their opponent and assess their fighting ability and have a reduced chance of winning. These anosmic subordinate fish also had an increase in pulse frequency, perhaps reflecting an increased effort in communication of status. Future research is needed to conclude if peaks in agonistic behavior are coordinated around the time of urea pules. However, the observed changes in behavior and pulsatile urea excretion due to anosmia in the present study provide evidence that toadfish use pulsatile urea excretion to release signals for chemical communication during agonistic encounters.

Effect of Winning Experience on Aggression Involving Dangerous Fighting Behavior in Anastatus disparis (Hymenoptera: Eupelmidae)

Aggressive behavior is widely observed in animal species for acquiring important resources and usually includes both dangerous and nondangerous fighting patterns. Only a few species show dangerous fighting patterns that are defined by fights ending with contestants being severely injured or killed. Prior experience, an important factor in many species, has been demonstrated to affect a contestant's subsequent fighting behavior. Few studies have focused on the effect of experience on aggression involving dangerous fighting patterns. Here, an egg parasitoid wasp, Anastatus disparis, which shows extreme and dangerous fighting behavior to acquire mating opportunities, was used as an experimental model. Our results showed that the fighting intensity of the winning males significantly decreased subsequent fighting behavior, which was inconsistent with general predictions. Transcriptomic analyses showed that many genes related to energy metabolism were downregulated in winners, and winners increased their fighting intensity after dietary supplementation. Our study suggested that fighting in A. disparis is a tremendous drain on energy. Thus, although males won at combat, significant reductions in available energy constrained the intensity of subsequent fights and influenced strategic decisions. In addition, winners might improve their fighting skills and abilities from previous contests, and their fighting intensity after dietary supplementation was significantly higher than that of males without any fighting experience. Generally, in A. disparis, although winners increased their fighting ability with previous experience, the available energy in winners was likely to be a crucial factor affecting the intensity and strategic decisions in subsequent fights.

Oil toxicity and implications for environmental tolerance in fish

Crude oil and its constituent chemicals are common environmental toxicants in aquatic environments worldwide, and have been the subject of intense research for decades. Importantly, aquatic environments are also the sites of numerous other environmental disturbances that can impact the endemic fauna. While there have been a number of attempts to explore the potential additive and synergistic effects of oil exposure and environmental stressors, many of these efforts have focused on the cumulative effects on typical toxicological endpoints (e.g. survival, growth, reproduction and cellular damage). Fewer studies have investigated the impact that oil exposure may have on the ability of exposed animals to tolerate typically encountered environmental stressors, despite the fact that this is an important consideration when placing oil spills in an ecological context. Here we review the available data and highlight potentially understudied areas relating to how oil exposure may impair organismal responses to common environmental stressors in fishes. We focused on four common environmental stressors in aquatic environments - hypoxia, temperature, salinity and acid-base disturbances - while also considering social stress and impacts on the hypothalamus-pituitary-interrenal axis. Overall, we believe the evidence supports treating the impacts of oil exposure on environmental tolerance as an independent endpoint of toxicity in fishes.

Social competition in red drum (Sciaenops ocellatus) is influenced by crude oil exposure

The present study examined impacts of crude oil exposure on dyad competition in juvenile red drum. Following the 2010 Deepwater Horizon oil spill, it has become well established that oil exposure can constrain maximum metabolic rate, reduce aerobic scope and exercise performance in marine fish. Aerobic scope is one of the physiological characteristics that is a known determinant of dominance in fish social hierarchy formation. As such, oil exposure may predispose individuals to subordinate social status, complete with the concomitant ecological costs. We tested this hypothesis on the gregarious Gulf of Mexico species, the red drum (Sciaenops ocellatus). Using a standard dyad, one-on-one, test design, we first assessed the parameters - including size and aerobic scope- that predict social dominance. Of the tested parameters, only aerobic scope was predictive of social dominance, with dominant individuals consistently having higher aerobic scopes than subordinates. Hierarchy formation between individuals exposed to one of two oil concentrations (5.7 ± 0.5 and 9.0 ± 0.2 μg l^-1 ΣPAH₅₀) and unexposed conspecifics were then investigated. As hypothesized, fish exposed to both oil concentrations were more likely to be subordinate than what would occur by random chance. These results demonstrate that the physiological constraints imposed by oil exposure can affect social status and behavior in fishes, which can have downstream consequences for ecological fitness.

Endocrine differences among colour morphs in a lizard with alternative behavioural strategies

Alternative behavioural strategies of colour morphs are expected to associate with endocrine differences and to correspond to differences in physical performance (e.g. movement speed, bite force in lizards); yet the nature of correlated physiological and performance traits in colour polymorphic species varies widely. Colour morphs of male tawny dragon lizards Ctenophorus decresii have previously been found to differ in aggressive and anti-predator behaviours. We tested whether known behavioural differences correspond to differences in circulating baseline and post-capture stress levels of androgen and corticosterone, as well as bite force (an indicator of aggressive performance) and field body temperature. Immediately after capture, the aggressive orange morph had higher circulating androgen than the grey morph or the yellow morph. Furthermore, the orange morph maintained high androgen following acute stress (30min of capture); whereas androgen increased in the grey and yellow morphs. This may reflect the previously defined behavioural differences among morphs as the aggressive response of the yellow morph is conditional on the colour of the competitor and the grey morph shows consistently low aggression. In contrast, all morphs showed an increase in corticosterone concentration after capture stress and morphs did not differ in levels of corticosterone stress magnitude (CSM). Morphs did not differ in size- and temperature-corrected bite force but did in body temperature at capture. Differences in circulating androgen and body temperature are consistent with morph-specific behavioural strategies in C. decresii but our results indicate a complex relationship between hormones, behaviour, temperature and bite force within and between colour morphs.

Hormonal Responses to Noncontact Aggression in Convict Cichlid Fish

This study explored whether convict cichlid fish mount a hormonal response to aggressive encounters where dominance status remains unresolved. Hormone samples were collected at two time points before an aggressive interaction to obtain confinement-induced and baseline measures, and at one time point following a contest across a clear partition (experimental) or exposure to an opaque partition with an opponent on the opposite side (control). There was no overall significant effect of treatment (control vs. experimental) on hormone release rates but there were trends for cortisol and testosterone (T). A priori linear contrasts showed that individuals that engaged in aggressive interactions had lower postfight cortisol and T release rates than controls, suggesting that aggression, in this context, might attenuate the synthesis of both hormones. Cortisol decreased significantly between initial confinement and baseline, indicating that individuals habituate to the water-borne hormone collection procedure. Contrary to expectation, individuals with higher baseline T and 11-ketotestosterone (KT) release rates took longer to initiate conflict. None of the other measures of behavior were predicted by baseline hormone release rates, and contest behavior did not predict postfight hormone release rates. There was a significant positive relationship between KT and T at all time points. As with studies that employ mirror image stimulation, we found no hormonal response to unresolved contests despite high levels of aggressive behavior. Our study is unique because we demonstrate that animals engaged in conflict with live opponents also do not mount a significant hormonal response when clear dominance relationships are not established.

Serotonergic outcome, stress and sexual steroid hormones, and growth in a South American cichlid fish fed with an L-tryptophan enriched diet

Reared animals for edible or ornamental purposes are frequently exposed to high aggression and stressful situations. These factors generally arise from conspecifics in densely breeding conditions. In vertebrates, serotonin (5-HT) has been postulated as a key neuromodulator and neurotransmitter involved in aggression and stress. The essential amino acid L-tryptophan (trp) is crucial for the synthesis of 5-HT, and so, leaves a gateway for indirectly augmenting brain 5-HT levels by means of a trp-enriched diet. The cichlid fish Cichlasoma dimerus, locally known as chanchita, is an autochthonous, potentially ornamental species and a fruitful laboratory model which behavior and reproduction has been studied over the last 15years. It presents complex social hierarchies, and great asymmetries between subordinate and dominant animals in respect to aggression, stress, and reproductive chance. The first aim of this work was to perform a morphological description of chanchita's brain serotonergic system, in both males and females. Then, we evaluated the effects of a trp-supplemented diet, given during 4weeks, on brain serotonergic activity, stress and sexual steroid hormones, and growth in isolated specimens. Results showed that chanchita's brain serotonergic system is composed of several populations of neurons located in three main areas: pretectum, hypothalamus and raphe, with no clear differences between males and females at a morphological level. Animals fed with trp-enriched diets exhibited higher forebrain serotonergic activity and a significant reduction in their relative cortisol levels, with no effects on sexual steroid plasma levels or growth parameters. Thus, this study points to food trp enrichment as a "neurodietary'' method for elevating brain serotonergic activity and decreasing stress, without affecting growth or sex steroid hormone levels.

Social status differences regulate the serotonergic system of a cichlid fish, Astatotilapia burtoni

Serotonin (5-HT) inhibits aggression and modulates aspects of sexual behaviour in many species, but the mechanisms responsible are not well understood. Here, we exploited the social dominance hierarchy of Astatotilapia burtoni to understand the role of the serotonergic system in long-term maintenance of social status. We identified three populations of 5-HT cells in dorsal and ventral periventricular pretectal nuclei (PPd, PPv), the nucleus of the paraventricular organ (PVO) and raphe. Dominant males had more 5-HT cells than subordinates in the raphe, but the size of these cells did not differ between social groups. Subordinates had higher serotonergic turnover in the raphe and preoptic area (POA), a nucleus essential for hypothalamic-pituitary-gonadal (HPG) axis function. The relative abundance of mRNAs for 5-HT receptor (5-HTR) subtypes 1A and 2A (htr1a, htr2a) was higher in subordinates, a difference restricted to the telencephalon. Because social status is tightly linked to reproductive capacity, we asked whether serotonin turnover and the expression of its receptors correlated with testes size and circulating levels of 11-ketotestosterone (11-KT). We found negative correlations between both raphe and POA serotonin turnover and testes size, as well as between htr1a mRNA levels and circulating 11-KT. Thus, increased serotonin turnover in non-aggressive males is restricted to specific brain nuclei and is associated with increased expression of 5-HTR subtypes 1A and 2A exclusively in the telencephalon.

Testosterone alters genomic responses to song and monoaminergic innervation of auditory areas in a seasonally breeding songbird

Behavioral responses to social stimuli often vary according to endocrine state. Our previous work has suggested that such changes in behavior may be due in part to hormone-dependent sensory processing. In the auditory forebrain of female white-throated sparrows, expression of the immediate early gene ZENK (egr-1) is higher in response to conspecific song than to a control sound only when plasma estradiol reaches breeding-typical levels. Estradiol also increases the number of detectable noradrenergic neurons in the locus coeruleus and the density of noradrenergic and serotonergic fibers innervating auditory areas. We hypothesize, therefore, that reproductive hormones alter auditory responses by acting on monoaminergic systems. This possibility has not been examined in males. Here, we treated non-breeding male white-throated sparrows with testosterone to mimic breeding-typical levels and then exposed them to conspecific male song or frequency-matched tones. We observed selective ZENK responses in the caudomedial nidopallium only in the testosterone-treated males. Responses in another auditory area, the caudomedial mesopallium, were selective regardless of hormone treatment. Testosterone treatment reduced serotonergic fiber density in the auditory forebrain, thalamus, and midbrain, and although it increased the number of noradrenergic neurons detected in the locus coeruleus, it reduced noradrenergic fiber density in the auditory midbrain. Thus, whereas we previously reported that estradiol enhances monoaminergic innervation of the auditory pathway in females, we show here that testosterone decreases it in males. Mechanisms underlying testosterone-dependent selectivity of the ZENK response may differ from estradiol-dependent ones

Primary and secondary sexual characters in alternative reproductive tactics of Chinook salmon: Associations with androgens and the maturation-inducing steroid

The proximate mechanisms that underlie the evolution of within-sex variation in mating behavior, sexual characters and reproductive investment patterns are still poorly understood. Species exhibiting alternative reproductive tactics (ARTs) are ideal model systems to examine these mechanisms. Chinook salmon (Oncorhynchus tshawytscha) exhibits two distinct ARTs: hooknoses, which are large males that establish spawning dominance hierarchies via intense male-male competition and jacks, which are smaller precocious sneaking males that steal fertilizations via sperm competition. In this study, we examine plasma testosterone (T), 11-ketotestosterone (11-KT) and maturation-inducing steroid (MIS; 17α,20β-dihydroxy-4-pregnen-3-one) profiles of spawning hooknoses and jacks. Furthermore, we examine relationships between androgens and primary (gonad mass, gonadosomatic index and sperm traits) and secondary (total mass, body size, hump depth and kype length) sexual characters. Relationships between MIS and sperm traits are also examined. We found that hooknoses and jacks did not significantly differ in terms of plasma T, 11-KT or MIS concentrations. Moreover, we found significant positive relationships between levels of both androgens within each ART. There were no significant relationships between androgens, MIS and sperm traits. T and 11-KT concentrations co-varied positively with gonad investment and kype length in jacks. In hooknoses, 11-KT concentration was positively related to total mass, hump depth and condition factor. Overall, these findings suggest that there are differential androgen effects for each of the ARTs in Chinook salmon.

Relationships between circulating androgens, aggressive behaviour and breeding tubercles in males of the common bream Abramis brama L. in an aquarium environment

In this study, relationships between circulating androgens, aggressive behaviour and breeding tubercles in males of common bream Abramis brama were examined in an aquarium environment. The breeding tubercles of fish were counted, the number of attacks was quantified by male status and circulating rates of testosterone and 11-ketotestosterone from blood plasma were analysed using radioimmunoassay procedures. The results revealed that no significant differences were found between circulating testosterone and 11-ketotestosterone in territorial and nonterritorial males. Furthermore, no significant correlations were found between circulating androgens, androgens and aggression, androgens and tubercles and breeding tubercles and aggression in common bream by male status. However, territorial fish displayed a significantly higher level of aggressive behaviour and breeding tubercles than nonterritorial fish. In natural environments, the occurrence of breeding tubercles during the spawning season could contribute to identifying the behavioural status of common bream males.

Higher levels of aggression are observed in socially dominant toadfish treated with the selective serotonin reuptake inhibitor, fluoxetine

The following study set out to test the hypothesis that acute treatment with the selective serotonin reuptake inhibitor, fluoxetine, would result in a rise in circulating 5-HT levels and consequently a decrease in territorial aggression in the Gulf toadfish, Opsanus beta. Size-matched pairs of toadfish were implanted intraperitoneally with the same dose of fluoxetine (0, 10 or 25 μg g⁻¹). After a social interaction between a pair of fish, circulating levels of serotonin (5-HT; 5-hydroxytryptamine) and cortisol were measured and relative mRNA expression of the 5-HT(1A) receptor in the toadfish brain was determined using quantitative (real-time) PCR (qPCR). Behavioral endpoints such as the number of aggressive acts and swimming activity were also quantified so that dominant and subordinate fish could be identified. Fluoxetine treatment resulted in an increase in circulating levels of 5-HT, regardless of social status. Circulating cortisol concentrations were unaffected by fluoxetine, but were significantly higher in subordinate individuals when compared to dominant fish. Toadfish brain 5-HT(1A) receptor mRNA expression was not affected by treatment or social status. Lastly and contrary to our predictions, fluoxetine treatment resulted in an increase in the number of aggressive acts made by dominant individuals, with no differences in the level of aggression or swimming activity of subordinate fish. This study is the first to describe elevated aggression in a teleost fish with elevated circulating levels of 5-HT.

Influences of sex and activity level on physiological changes in individual adult sockeye salmon during rapid senescence

A noninvasive biopsy protocol was used to sample plasma and gill tissue in individual sockeye salmon (Oncorhynchus nerka) during the critical life stage associated with spawning-arrival at a spawning channel through senescence to death several days later. Our main objective was to characterize the physiological changes associated with rapid senescence in terms of the physiological stress/cortisol hypersecretion model and the energy exhaustion model. Salmon lived an average of 5 d in the spawning channel, during which time there were three major physiological trends that were independent of sexual status: a large increase in plasma indicators of stress and exercise (i.e., lactate and cortisol), a decrease in the major plasma ions (i.e., Cl(-) and Na(+)) and osmolality, and a decrease in gross somatic energy reserves. Contrary to a generalized stress response, plasma glucose decreased in approximately 2/3 of the fish after arrival, as opposed to increasing. Furthermore, plasma cortisol levels at spawning-ground arrival were not correlated with the degree of ionoregulatory changes during rapid senescence. One mechanism of mortality in some fish may involve the exhaustion of energy reserves, resulting in the inability to mobilize plasma glucose. Sex had a significant modulating effect on the degree of physiological change. Females exhibited a greater magnitude of change for gross somatic energy, osmolality, and plasma concentrations of Cl(-), Na(+), cortisol, testosterone, 11-ketotestosterone, 17,20beta-progesterone, and estradiol. The activity level of an individual on the spawning grounds appeared to influence the degree of some physiological changes during senescence. For example, males that received a greater frequency of attacks exhibited larger net decreases in plasma 11-ketotestosterone while on the spawning grounds. These results suggest that rapid senescence on spawning grounds is influenced by multiple physiological processes and perhaps behavior. This study provides some of the first data to look at sex differences in senescence in Pacific salmon.

Effects of chronic exposure to ammonia concentrations on brain monoamines and ATPases of Nile tilapia (Oreochromis niloticus)

The effects of chronic exposure to total ammonia nitrogen (TAN) concentrations on the brain monoamines and ATPases of Nile tilapia, Oreochromis niloticus fingerlings, were studied. The period of exposure was 70 consecutive days, and the initial weight of the fingerlings was 18+/-2.1g. In addition to the control, three treatment groups exposed to 2.5 (low), 5 (medium), and 10 (high) mg TANL(-)(1) concentrations were tested. The unionized ammonia nitrogen (NH(3)) levels calculated in mgL(-)(1) were 0.059, 0.185, and 0.575 in aquaria at 26 degrees C. The brain monoamines were serotonin (5-HT), dopamine (DA), and norepinephrine (NE), as well as their derivatives, 5-hydroxyindoleacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC). Compared with the controls, the levels of brain monoamines and Na(+)/K(+)- and Ca(2+)-ATPase activities were not significantly altered in fish exposed to low TAN concentration. However, there was a significant decrease in 5-HT, DA, and NE levels, and a significant increase in both serotonergic (5-HIAA/5-HT) and dopaminergic (DOPAC/DA) activities of fish exposed to medium TAN and high TAN concentrations. The activities of brain Na(+)/K(+)- and Ca(2+)-ATPases of fish exposed to medium TAN and high TAN concentrations significantly increased, while Mg(2+)-ATPase did not significantly change compared with that of the controls. The quantity of the detected alterations increased in fish exposed to high TAN concentration.

A multivariate comparison of the stress response in three salmonid and three cyprinid species: evidence for inter-family differences

The response of six species of freshwater fishes, from the families Cyprinidae (common carp Cyprinus carpio, roach Rutilus rutilus and chub Leuciscus cephalus) and Salmonidae (rainbow trout Oncorhynchus mykiss, brown trout Salmo trutta and Arctic charr Salvelinus alpinus), to a standardized stressor was evaluated. A 6 h period of confinement resulted in changes to plasma cortisol, glucose, amino acid and lactate levels compared with unconfined controls. There were significant differences in the response profiles both within and between families. The cyprinid species exhibited higher and more sustained stress-induced increases in plasma cortisol and glucose than the salmonid species. In cyprinids, plasma lactate and plasma amino acid concentration showed less disturbance following stress than in salmonids. The results of the study, together with an evaluation of previously published data for eight salmonid species and six cyprinid species, support the hypothesis that differences in core elements of the stress response exist between species of fishes, and that this variation may have a systematic basis.

The role of the maturation-inducing steroid, 17,20beta-dihydroxypregn-4-en-3-one, in male fishes: a review

The major progestin in teleosts is not progesterone, as in tetrapods, but 17,20beta-dihydroxypregn-4-en-3-one (17,20beta-P) or, in certain species, 17,20beta,21-trihydroxy-pregn-4-en-3-one (17,20beta,21-P). Several functions for 17,20beta-P and 17,20beta,21-P have been proposed (and in some cases proved). These include induction of oocyte final maturation and spermiation (milt production), enhancement of sperm motility (by alteration of the pH and fluidity of the seminal fluid) and acting as a pheromone in male cyprinids. Another important function, initiation of meiosis (the first step in both spermatogenesis and oogenesis), has only very recently been proposed. This is a process that takes place at puberty in all fishes and once a year in repeat spawners. The present review critically examines the evidence to support the proposed functions of 17,20beta-P in males, including listing of the evidence for the presence of 17,20beta-P in the blood plasma of male fishes and discussion of why, in many species, it appears to be absent (or present at low and, in some cases, unvarying concentrations); consideration of the evidence, obtained mainly from in vitro studies, for this steroid being predominantly produced by the testis, for its production being under the control of luteinizing hormone (gonadotrophin II) and, at least in salmonids, for two cell types (Leydig cells and sperm cells) being involved in its synthesis; discussion of the factors involved in the regulation of the switch from androgen to 17,20beta-P production that seems to occur in many species just at the time of spermiation; discussion of the effects of in vivo injection and application of 17,20beta-P (and closely related compounds) in males; a listing of previously published evidence that supports the proposed new function of 17,20beta-P as an initiator of meiosis; finally, discussion of the evidence for environmental endocrine disruption by progestins in fishes.

Social competition affects electric signal plasticity and steroid levels in the gymnotiform fish Brachyhypopomus gauderio

Sexually-selected communication signals can be used by competing males to settle contests without incurring the costs of fighting. Steroid regulation of these signals can render them as reliable indicators of a male's physiological state. We investigated how plasticity in electrocommunication signals is driven by social competition for mates, mediated by steroid hormones, and subject to the effects of past social experience. We measured the electric waveform's amplitude and duration and steroid hormone levels of male gymnotiform electric fish (Brachyhypopomus gauderio) following week-long periods of social isolation, and low or high social competition. To quantify the effect of social history on the modulation of the electric signal, six groups of six males experienced all three social conditions but in different order. We found that males differentially modulate their electric signals depending on the order they experienced these conditions. Thus, past social interactions affect both present and future social electric signals. Cortisol levels and the amplitude of the electric signal appeared to track the intensity of competition, while androgen levels and the duration of the electric signal only responded to the presence (low and high competition) or absence (isolation) of a social environment (low and high androgens respectively). In addition, cortisol levels were related to the body size of the males at high social competition. Taken together, these findings suggest that the capacity of males to modulate their signals in response to social competition is regulated by steroids.

Establishment of dominance relationships in gilthead sea bream Sparus aurata juveniles during feeding: effects on feeding behaviour, feed utilization and fish health

In gilthead sea bream Sparus aurata held in groups of two, five or 10 fish, social hierarchies were observed. Subordinate S. aurata were characterized by elevation of basal levels of plasma cortisol, together with a reduced immunological potential. Subordinate fish also showed lower feed intake, feed utilization and lower growth. Fatty acid composition was also affected by social status, with a lower content of saturated acids, oleic and eicosapentaenoic, in muscle and liver of fish considered as subordinate. Results show that social hierarchy acts as a stressor in S.aurata.

Physiological endpoints for potential SSRI interactions in fish

Selective serotonin reuptake inhibitors (SSRIs) are among the pharmaceutical compounds frequently detected in sewage treatment plant effluents and surface waters, albeit at very low concentrations, and have therefore become a focus of interest as environmental pollutants. These neuroactive drugs are primarily used in the treatment of depression but have also found broader use as medication for other neurological dysfunctions, consequently resulting in a steady increase of prescriptions worldwide. SSRIs, via inhibition of the serotonin (5-hydroxytryptamine, 5-HT) reuptake mechanism, induce an increase in extracellular 5-HT concentration within the central nervous system of mammals. The phylogenetically ancient and highly conserved neurotransmitter and neurohormone 5-HT has been found in invertebrates and vertebrates, although its specific physiological role and mode of action is unknown for many species. Consequently, it is difficult to assess the impact of chronic SSRI exposure in the environment, especially in the aquatic ecosystem. In view of this, the current knowledge of the functions of 5-HT in fish physiology is reviewed and, via comparison to the physiological role and function of 5-HT in mammals, a characterization of the potential impact of chronic SSRI exposure on fish is provided. Moreover, the insight on the physiological function of 5-HT strongly suggests that the experimental approaches currently used are inadequate if not entirely improper for routine environmental risk assessment of pharmaceuticals (e.g., SSRIs), as relevant endpoints are not assessed or impossible to determine.

Reciprocity between endocrine state and contest behavior in the killifish, Kryptolebias marmoratus

Given the dramatic behavioral effects of winning and losing contests, and pronounced changes in stress and sex steroid hormones post-fight, it is reasonable to suppose that these hormones also dictate future behavior. We sampled water-borne cortisol, testosterone (T), and 11-ketotestosterone (KT) before and after contests in the mangrove killifish, Kryptolebias marmoratus, to determine how endogenous steroid hormone levels might predict and respond to contest dynamics or success. Pre-fight cortisol related negatively, and pre-fight T related positively to contest initiation and winning, particularly in the smaller opponent. In the pairs where a larger fish won the contest, winners with higher pre-fight T and lower pre-fight cortisol delivered more attacks to the losers. Contest duration and escalation influenced post-fight hormone concentrations primarily in losers. Escalation significantly increased post-fight cortisol, T, and KT for losers but not for winners. However, winners that attacked losers at higher rates had higher levels of post-fight cortisol. Losers also demonstrate the most consistent post-fight hormone responses, particularly to contest escalation and duration. Despite the bidirectional relationship between hormones and contest behavior, we found no overall mean differences in pre- or post-fight cortisol, T, or KT between eventual winners and losers. Thus, it is evident that the categorical states of winner and loser cannot alone reveal the complex, reciprocal associations between endocrine systems and social behavior.

Sex steroids and their receptors in lampreys

The use of steroids and their receptors as ligand-gated transcription factors is thought to be an important step in vertebrate evolution. The lamprey is the earliest-evolving vertebrate to date in which sex steroids and their receptors have been demonstrated to have hormonal roles similar to those found in jawed vertebrates. Sex steroids and their receptors have been examined in several lamprey species, and the majority of studies have focused on the sea lamprey, Petromyzon marinus. While classical steroids appear to be present in lampreys, their function, concentrations, and synthesis have not been determined conclusively. The only classical steroid that is thought to act as a hormone in both males and females is estradiol. Recent research has established that lampreys produce and circulate 15alpha-hydroxylated steroids, and that these steroids respond to upstream stimulation within the hypothalamic-pituitary-gonadal axis. In particular, 15alpha-hydroxyprogesterone is highly sensitive and responds in great magnitude to stimulation, and is likely a hormone. Lampreys also appear to use androstenedione, a precursor to vertebrate androgens, as their main androgen, and a receptor for androstenedione has recently been described. Non-classical steroids are prevalent in many aquatic vertebrates, and the non-classical steroids found in the sea lamprey may represent an evolutionary artifact, or alternatively may be a way to avoid endocrine disruption when ingesting the body fluids of host fish. The lamprey will continue to be an interesting model for examining the evolution of steroid hormones, steroid receptors, and steroid function.

Hormone levels in territorial and non-territorial male collared lizards

For species displaying plastic alternative reproductive tactics, the relative plasticity hypothesis (RPH) combined with the positive relationship between androgens and aggression predicts higher androgen levels in more aggressive socially dominant males relative to less aggressive subordinate males (directional RPH). We tested this prediction of the directional RPH by comparing plasma levels of testosterone, dihydrotestosterone, and corticosterone in 2y+-collared lizard males that defended territories with those of first-year males that were mature, but did not defend territories. As expected, 2y+-males exhibited higher rates of advertisement, aggression, and courtship than first-year males. Contrary to expectations of the directional RPH, levels of testosterone, dihydrotestosterone and corticosterone were similar in the males displaying these alternative tactics. Furthermore, whereas display by non-territorial males increased after a neighboring territorial male died, levels of testosterone and corticosterone decreased in these males, counter to prediction that the territorial tactic is activated by increased androgens. This result also suggests that high rates of aggression do not alter plasma steroids, although behavioral manipulations are needed to more fully test this hypothesis. Secretion of testosterone in non-territorial males may promote their high growth rates, and/or may prime them for the rapid behavioral changes that occur when opportunities for territory acquisition arise as a consequence of predation on territorial males. Relationships among hormones differed between these types of males: corticosterone was negatively correlated with both testosterone and dihydrotestosterone in territorial males, but androgens and corticosterone did not significantly covary in non-territorial males.

Social Regulation of Neurogenesis in Teleosts

Salmonid fishes such as the rainbow trout (Oncorhynchus mykiss) are frequently used to study behavioral and neuroendocrine effects of socially induced stress. A predictable aggressive response to territorial intrusion, a well described neuroanatomy, and many essential similarities in the stress response in fishes and other vertebrates are among the advantages of this comparative model. One conspicuous difference when compared to mammals, however, is that in teleost fish and other non-mammalian vertebrates, neurogenesis persists into adulthood to a much higher degree. Very little is known about the functional significance of individual differences in the rate of brain cell proliferation in fish, or whether structural changes in the fish brain are influenced by the social environment. In this paper we discuss the observation that brain cell proliferation is reduced in subordinate fish, focusing in particular on whether such individual variation reflects a difference in coping style or is indeed a response to social interactions.

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks

Variable neuroendocrine responses to ecologically-relevant challenges in sticklebacks. PHYSIOL BEHAV 00(0) 000-000, 2006. Here, we compare the behavioral, endocrine and neuroendocrine responses of individual sticklebacks exposed to either an unfamiliar conspecific or to a predator. We found that the two stressors elicited a similar hypothalamic-pituitary-interrenal response as assessed by whole-body concentrations of cortisol, but produced quite different patterns of change in brain monoamine and monoamine metabolite content as assessed by concentrations of serotonin (5-HT), dopamine (DA), norepinephrine (NE) and the monoamine metabolites 5-hydroxyindole acetic acid (5-HIAA), homovanillic acid (HVA) and 3-4-dihydroxyphenylacetic acid (DOPAC). For example, relative to baseline levels, NE levels were elevated in individuals exposed to a predator but were lower in individuals confronted by a challenging conspecific. Levels of monoamine neurotransmitters in specific regions of the brain showed extremely close links with behavioral characteristics. Frequency of attacking a conspecific and inspecting a predator were both positively correlated with concentrations of NE. However, whereas serotonin was negatively correlated with frequency of attacking a conspecific, it was positively associated with predator inspection. The data indicate that the qualitative and quantitative nature of the neuroendocrine stress response of sticklebacks varies according to the nature of the stressor, and that interindividual variation in behavioural responses to challenge are reflected by neuroendocrine differences.

Behavioral and neurophysiological responses of European sea bass groups reared under food constraint

The individual food-demand behavior of juvenile European sea bass (Dicentrarchus labrax, L.) reared in groups under self-feeding conditions was investigated. The triggering activity on self-feeder, i.e. index of the food-demand activity, agonistic interactions and territorial behavior were monitored for periods of 42 to 68 days in six groups of 50 fish. The specific growth rate was calculated and the brain serotonergic activity was used as a stable index of social stress. Inter-individual differences appeared in triggering activity and three groups were distinguished: 3-5 high-triggering fish, 17-30 low-triggering fish and the remaining individuals were null-triggering fish. There were no significant differences in specific growth rates calculated at the end of the experiment (day 42 or day 68) between individuals with high, low, and null food-demand (ANOVA, p>0.05). No territorial or agonistic behaviors were observed, however, there were significant differences in brain serotonergic activity between the three triggering groups (ANOVA, p=0.050 in telencephalon and p=0.004 in cerebellum). Specifically, high-triggering fish had lower serotonergic turnover than low or null-triggering fish. We put forth the hypothesis that fish with low or null-triggering activity could be stressed by the high activity of high-triggering individuals.

Testosterone change after losing predicts the decision to compete again

Testosterone (T) levels can fluctuate after wins and losses, but surprisingly, there are no empirical studies in humans that have tested whether these post-competition T changes predict the social behaviors that follow. The present study examined whether changes in T after losing in a competition predicted who wanted to compete again in a second competition. Sixty-four males provided saliva samples immediately before and 15 min after a rigged one-on-one competition. After the second saliva sample, participants chose whether or not to compete again against the same competitor. Winners did not increase in T relative to losers, but pre-competition cortisol, change in cortisol, and pre-competition T were associated with T changes, especially in losers. Importantly, changes in T predicted decisions to compete again in losers. Losers who increased in T were more likely to choose to compete again than losers who decreased in T. T changes were unrelated to decisions to compete again in winners. These findings provide novel data in humans that T changes after a status loss predict subsequent social behavior. Our discussion focuses on the theoretical implications of these findings for the link between short-term T changes and status-related behaviors.

The mismatch effect: when testosterone and status are at odds

Why do some people strive for high status, whereas others actively avoid it? In the present studies, the authors examined the psychological and physiological consequences of a mismatch between baseline testosterone and a person's current level of status. The authors tested this mismatch effect by placing high and low testosterone individuals into high or low status positions using a rigged competition. In Study 1, low testosterone participants reported greater emotional arousal, focused more on their status, and showed worse cognitive functioning in a high status position. High testosterone participants showed this pattern in a low status position. In Study 2, the emotional arousal findings were replicated with heart rate, and the cognitive findings were replicated using a math test. In Study 3, the authors demonstrate that testosterone is a better predictor of behavior than self-report measures of the need for dominance. Discussion focuses on the value of measuring hormones in personality and social psychology.

Growth Depression in Socially Subordinate Rainbow TroutOncorhynchus mykiss: More than a Fasting Effect

To assess the effects of subordinate social status on digestive function, metabolism, and enzyme activity in salmonid fish, juvenile rainbow trout Oncorhynchus mykiss were paired with size-matched conspecifics (<1.5% difference in fork length) for 5 d. Fish that were fasted for 5 d and fish sampled directly from the holding tank were used as control groups. Both subordinate and fasted fish experienced significant decreases in intestine mass (P = 0.043), and the gall bladder showed marked and significant changes in both size (P = 0.004) and appearance. These findings suggest that the negative effect of social subordination on digestive function reflects in large part a lack of feeding. Hepatic phosphoenolpyruvate carboxykinase activity was significantly higher in subordinate fish relative to dominants, whereas subordinate hepatic pyruvate kinase activity was significantly lower; activities of both enzymes were significantly correlated with plasma cortisol concentrations and behavior scores. Dominant-subordinate differences in the activities of these enzymes were eliminated by administration of the glucocorticoid receptor antagonist RU486, underlining a role for circulating cortisol in eliciting the differences. Significant increases relative to control fish were also detected in red and white muscles from subordinate fish in the activities of protein catabolic enzymes (aspartate aminotransferase, alanine aminotransferase, glutamate dehydrogenase). These differences occurred in the absence of any change in plasma free amino acid or ammonia concentrations, supporting an enhanced turnover of amino acids in muscle in subordinate fish. The results support the hypothesis that changes in metabolism, beyond those elicited by low food consumption, may be responsible at least in part for the low growth rates typical of subordinate fish and that these changes may be related specifically to circulating cortisol levels in subordinate fish.

Male 11-ketotestosterone levels change as a result of being watched in Siamese fighting fish, Betta splendens

This study investigated the effects of nesting status and the presence of an audience on 11-ketotestosterone (11KT) levels in male Siamese fighting fish, Betta splendens. Prior studies have demonstrated that both nesting status, an indicator of territory-holding power and reproductive state, and the sex of a conspecific audience lead to differences in male behavior during aggressive encounters. Since behavioral changes have already been demonstrated, we chose to investigate whether 11KT levels were also influenced by nesting status and audience presence as 11KT both stimulates, and is stimulated by, reproductive and aggressive behaviors in male teleosts. Male 11KT levels were measured from water samples taken from containers holding fish both before and after interaction. Males interacted under three treatment conditions: no audience, female audience, and male audience. Within these treatments were two nest paradigms: both males had nests or neither male had a nest. 11KT levels varied depending on nesting status and audience type. In general, 11KT levels were lower in interacting males when a female audience was present or when males had nests. Overall, 11KT showed increases or decreases as aggression increased or decreased, as shown by already established behavioral findings [see Dzieweczynski T.L., Green T.M., Earley R.L., Rowland W.J., 2005. Audience effect is context dependent in Siamese fighting fish, Betta splendens. Behav. Ecol. 16, 1025-1030; Doutrelant, C., McGregor, P.K., Oliveira, R.F., 2001. Effect of an audience on intrasexual communication in male Siamese fighting fish (Betta splendens). Behav. Ecol. 12, 283-286.]. Our results suggest that 11KT levels are influenced by reproductive status, as indicated by nest ownership, and audience presence and are most likely modulated by territorial behavior and social environment.

Glucocorticoid interaction with aggression in non-mammalian vertebrates: reciprocal action

Socially aggressive interaction is stressful, and as such, glucocorticoids are typically secreted during aggressive interaction in a variety of vertebrates, which may both potentiate and inhibit aggression. The behavioral relationship between corticosterone and/or cortisol in non-mammalian (as well as mammalian) vertebrates is dependent on timing, magnitude, context, and coordination of physiological and behavioral responses. Chronically elevated plasma glucocorticoids reliably inhibit aggressive behavior, consistent with an evolutionarily adaptive behavioral strategy among subordinate and submissive individuals. Acute elevation of plasma glucocorticoids may either promote an actively aggressive response via action in specialized local regions of the brain such as the anterior hypothalamus, or is permissive to escalated aggression and/or activity. Although the permissive effect of glucocorticoids on aggression does not suggest an active role for the hormone, the corticosteroids may be necessary for full expression of aggressive behavior, as in the lizard Anolis carolinensis. These effects suggest that short-term stress may generally be best counteracted by an actively aggressive response, at least for socially dominant proactive individuals. An acute and active response may be evolutionarily maladaptive under chronic, uncontrollable and unpredictable circumstances. It appears that subordinate reactive individuals often produce compulsorily chronic responses that inhibit aggression and promote submissive behavior.