Fighting cichlids: An integrated multimodal analysis to understand female and male aggression in Cichlasoma dimerus.

Aggression has been historically linked to males and androgen levels and, even if females from different species also display aggressive behavior, female aggression is still widely understudied. The aim of the present work is to disentangle how sex differences in social plasticity can be explained by sex steroid hormone levels, gonadal state and/or morphometric characteristics. In this context, we performed intrasexual dyadic encounters to identify social plasticity after acquiring a winner or loser status in males and females of Cichlasoma dimerus. This integral analysis suggests that the reproductive and hormonal variables analyzed explain the behavioral variation among winner and loser males and females, and that there are significant differences between sexes and contest outcome when individual morphometric variables are excluded from the analysis. Interestingly, there are no sex differences in aggressive and submissive behaviors, and clustering into winners and losers is mainly explained by specific behavioral displays, such as bites, chases, approaches, passive copings, and escapes. Correlation heatmaps show a positive correlation between estradiol with aggression and a negative correlation with submission, suggesting estrogens may have a dual role regulating agonistic behavior. Finally, these results suggest that size difference can help to understand aggression in females but not in males, and that assessment of the opponent's body size is important to understand aggression also before the initiation of the contest in both sexes. Overall, this study constitutes an integral approach adding insights into the importance of reproductive and hormonal variables to understand social plasticity in males and females.

Ultrastructural and immunohistochemical characteristics of the olfactory organ cardinal tetra, Paracheirodon axelrodi (Characiformes: Characidae).

The cardinal tetra Paracheirodon axelrodi belongs to the family Characidae, an economically important and morphologically diverse family of fishes. Information on the olfactory system of this species is scattered and scarce. Among teleost fishes, differences exist in the shape, number, and arrangement of the olfactory lamellae, in the distribution of the sensory and nonsensory epithelium, as well as in the abundance of various receptor cell types. Here, an anatomical and morphological description of the olfactory system was carried out using light microscopic histology, immunohistochemistry, scanning electron microscopy, and transmission electron microscopy. P. axelrodi is a ditremous and isosmat species. It has an arrow-shaped olfactory rosette arrangement. The olfactory epithelium is covering the 12-14 lamellae of the olfactory rosette and, using scanning electron microscopy, we observed that the apical surface of the olfactory epithelium carries a dense layer of mucus. Based on the histological, immunohistochemical, and ultrastructural descriptions, all characteristic sensory and nonsensory cell types of the olfactory epithelium of teleost fish were identified. Three types of olfactory receptor neurons were identified: ciliated, microvilli, and crypt cells. The distribution of sensory and nonsensory cell types is like that described in Aphyocharax anisitsi, another species of the Characidae family. A. anisitsi inhabits slow-flowing water bodies with high-density vegetation such as P. axelrodi.

Effects of intraspecific chemical cues on the behaviour of the bloodfin tetra Aphyocharax anisitsi (Ostariophysi: Characidae).

Chemical communication can induce a multitude of behaviours when detected by fish olfactory systems, from parental care, predation and alarm signalling, to foraging, schooling, reproduction, and migration. Chemical cues provide information that visual traits cannot and fish can respond to chemical cues without any additional sensory cue. In this way, pheromones play an essential role in the fitness of fishes. Given that Aphyocharax anisitsi inhabits environments characterized by cloudy and highly vegetated waters, it is interesting to evaluate the olfactory contribution in their communication. Here, we investigated the relevance of chemical cues in the types of behaviours triggered in A anisitsi by two experimental contexts: 1) non-social and olfactory context (conspecific-chemical cues), and 2) social context (conspecific female or male presence). Non-social context experiments suggest that males of A. anisitsi respond to both male and female-chemical cues even in the absence of other sensory inputs. The high olfactory sensitivity of characids in general and of A. anisitsi, in particular, could facilitate vital functions, such as foraging and conspecific recognition in habitats that impose severe restrictions on the visual system.

Sexual Dimorphism in Aggression: Sex-Specific Fighting Strategies Across Species.

Aggressive behavior is thought to have evolved as a strategy for gaining access to resources such as territory, food, and potential mates. Across species, secondary sexual characteristics such as competitive aggression and territoriality are considered male-specific behaviors. However, although female-female aggression is often a behavior that is displayed almost exclusively to protect the offspring, multiple examples of female-female competitive aggression have been reported in both invertebrate and vertebrate species. Moreover, cases of intersexual aggression have been observed in a variety of species. Genetically tractable model systems such as mice, zebrafish, and fruit flies have proven extremely valuable for studying the underlying neuronal circuitry and the genetic architecture of aggressive behavior under laboratory conditions. However, most studies lack ethological or ecological perspectives and the behavioral patterns available are limited. The goal of this review is to discuss each of these forms of aggression, male intrasexual aggression, intersexual aggression and female intrasexual aggression in the context of the most common genetic animal models and discuss examples of these behaviors in other species.

Effect of previous fighting on the dynamic of agonistic encounters in zebrafish males.

Aggression among individuals which compete for resources such as food or territory, or to establish dominance relationships, can cause injuries that may be risky for the contenders. In this way, individuals of many species have strategies to resolve conflicts reducing levels of aggression. Thus, if individuals are able to recognize each other and remember previous agonistic experiences and the result of the fight, they will resolve the subsequent encounter with lower levels of aggression. Here, we evaluated the effect of previous fighting experiences (24 h interval) on agonistic behaviors of subsequent encounters in zebrafish (Danio rerio) males. Specifically, we examined if any reduction in aggression is because of an individual's ability to remember other individuals from previous interactions, or if reductions come directly from winning or losing a fight. We found that when a pair of opponents (of the same size) had fought, and 24 h later the same dyad fought again, the number of bites decreases 85% and the duration of aggression decreases 73% in the second encounter, and this effect persisted in a third encounter (a decrease of 90% and 95%, respectively). To evaluate if the effect of previous experience on agonistic behaviors depended on facing the same opponent, in the second fight of a new experiment the opponent was changed. In this case, no decreases in the number of bites or in the duration of aggression was observed. In conclusion, pairs of zebrafish males resolve a conflict with lower levels of aggression when having previously fought with that particular opponent, but not with an unknown opponent. As a whole, these results suggest that zebrafish males are capable of recognizing the opponent, remembering previous experiences and changing their fighting strategies accordingly, but not only as a consequence of the result of a previous encounter.

Morphology and immunohistochemistry of the olfactory organ in the bloodfin tetra, Aphyocharax anisitsi (Ostariophysi: Characidae).

Among teleost fishes, differences exist in the shape, number, and arrangement of the olfactory lamellae, the distribution of the sensory and non-sensory epithelium, as well as, the abundance of various receptor cells. The objective of this work was to describe the morphology, immunohistochemistry, and scanning electron microscopy ultrastructure of the olfactory epithelium of the bloodfin tetra, Aphyocharax anisitsi. This is the first complete description including the anatomy, histology, and immunohistochemistry of the peripheral olfactory organ from a Characiformes. Based on the external morphology of the olfactory organ, A. anisitsi was classified as a ditermous species, with an olfactory cavity containing two openings divided by a skin flap that separates the anterior and posterior nostril. This species belongs to the group of isosmates, since the presence of accessory olfactory sacs was not observed, and non-sensory ciliated cells were identified. A. anisitsi has an olfactory rosette with an arrow-shaped arrangement, with differences in length between the anterior and posterior lamellae. In the olfactory epithelium, three types of olfactory receptor neurons were identified using histology and confirmed by immunohistochemistry, that is, ciliated olfactory receptor neurons in the basal region of the epithelium, microvillar olfactory receptor neurons in the middle region; and Crypt cells, in smaller numbers compared to the other neuronal types, present in the apical region. Sensory and non-sensory areas were scattered and mixed along the lamellar lateral surface but the nasal cavity and the midline raphe lacked olfactory receptor neurons. The presence of abundant kinocilia in the non-sensory cells could be related in A. anisitsi with ventilation and quality control of water entering the olfactory cavity. The spatial organization of the sensory and non-sensory areas in A. anisitsi was similar to that observed in other species that also inhabit still and slow-flowing bodies of water with high-density vegetation.

Social control of spermatogenesis and steroidogenesis in cichlid fish: a comparative approach.

Social animals with hierarchical dominance systems are susceptible to changes their environment. Interactions with conspecifics can greatly affect individual's behavior and reproductive success. This review will show how social behavior modulates gonadal steroidogenesis and spermatogenesis in African and Neotropical cichlid fish with different social systems and how this modulation regulates reproductive capacity. Social behavior and aggressiveness are strongly linked to sex steroids, glucocorticoids and neuropeptides. The challenge hypothesis suggests that behavioral interactions increase androgen levels in response to social instability, but there is little evidence regarding estradiol levels. It has been recently demonstrated that in male Cichlasoma dimerus, a Neotropical cichlid fish, the challenge hypothesis could also be extended to estrogens. In C. dimerus, dominant males have higher gonadosomatic index than subordinated; the percentage of spermatocytes and spermatids is higher in subordinates, while dominants show a greater percentage of spermatozoa. In other species of African cichlids, socially suppressed subordinate males are not reproductively incompetent maintaining some activity at every level of their reproductive axis. Axis reactivation upon social ascent is similar to the initiation of puberty in mammals, as well as the reoccurrence of puberty observed in seasonally breeding animals. In conclusion, social behavior and reproductive strategies in females cichlids are still understudied, and Neotropical cichlids still constitute a group that deserves more attention, considering cichlids' diversity in mating systems, reproductive behavior and parental care. This review highlights the importance of performing further studies and additional research in these two areas, which still remain to be addressed.

Morphological and immunohistochemical comparison of the pituitary gland between a tropical Paracheirodon axelrodi and a subtropical Aphyocharax anisitsi characids (Characiformes: Characidae)

Cardinal tetra Paracheirodon axelrodi and bloodfin tetra Aphyocharax anisitsi are two species of characids with high trade value as ornamental fish in South America. Although both species inhabit middle water layers, cardinal neon exhibits a tropical distribution and bloodfin tetra a subtropical one. Generally, these species are difficult to grow, so it becomes essential to know some key components of the neuroendocrine system to achieve their reproduction in captivity. Considering the importance of deepening the knowledge of the reproductive physiology through functional morphology, for the first time in this work we performed an anatomical, morphological and immunohistochemical analysis of the pituitary gland of these two species. In both species, a leptobasic type pituitary is found in the ventral zone of the hypothalamus and it is characterized by a neurohypophysis which has a well-developed pituitary stalk and a globular adenohypophysis. The pituitary components, characterized by histochemistry and immunohistochemistry, shows a distribution pattern of cells types similar to other teleost species, with only slight differences in the distribution of βFSH and βLH for P. axelrodi.(AU)

El cardenal tetra Paracheirodon axelrodi y el tetra Aphyocharax anisitsi son dos especies de carácidos con alto valor comercial como peces ornamentales en América del Sur. Aunque ambas especies habitan en las capas medias de agua, el neón cardenal exhibe una distribución tropical, mientras que el tetra cola roja una distribución subtropical. En general estas especies son difíciles de cultivar, por lo que es esencial conocer algunos componentes clave de los sistemas neuroendocrinos para lograr su reproducción en cautiverio. Considerando la importancia de profundizar en el conocimiento de la fisiología reproductiva a través de la morfología funcional, en este trabajo realizamos, por primera vez, un análisis anatómico, morfológico e inmunohistoquímico de la glándula pituitaria de estas dos especies. En ambas especies, la hipófisis, del tipo leptobásica, se encontró en la zona ventral del hipotálamo y se caracteriza por una neurohipófisis con un tallo hipofisario bien desarrollado y una adenohipófisis globular. Los componentes hipofisarios, caracterizados por la histoquímica y la inmunohistoquímica, mostraron un patrón de distribución de tipos de células similares a otras especies de teleósteos, con solo pequeñas diferencias en la distribución de βFSH y βLH para P. axelrodi.(AU)

Vasotocinergic control of agonistic behavior told by Neotropical fishes.

The hypothalamic neuropeptides of the vasopressin-oxytocin family (and their homologs for non-mammalian species) are key modulators of the Social Brain Network, acting via specific receptors reported in all the nuclei of this network. Different conclusive examples have proven the context-dependency actions of hypothalamic nonapeptides on social behavior in several vertebrate taxa. Teleost fishes provide endless possibilities of experimental model systems to explore the underlying mechanisms of nonapeptide actions on social behavior given that they are the most diverse group of vertebrates. Although it has been difficult to identify commonalities of nonapeptide actions across species, indisputable evidence in many teleost species have demonstrated a clear role of vasotocin in the modulation of aggressive and sexual behaviors. Though Neotropical South American fish contribute an important percentage of teleost diversity, most native species remain unexplored as model systems for the study of the neuroendocrine bases of social behavior. In this review, we will revise recent data on the two model systems of Neotropical fish, South American cichlids and weakly electric fish that have contributed to this issue.

Characterization of the gonadotropin-releasing hormone system in the Neotropical teleost, Steindachneridion parahybae during the annual reproductive cycle in captivity.

This study evaluated by immunohistochemical and Western blot methods, the distribution of two distinct gonadotropin-releasing hormones (GnRHs), corresponding to catfish GnRH (cfGnRH or GnRH1) and chicken-II GnRH (cGnRH-II or GnRH2), in Steindachneridion parahybae females in captivity, focusing these analyses on the reproductive cycle by semi-quantification of optical density (OD). Further, we found that the GnRH neuronal systems co-localized with their respective GnRH-associated peptides (GAPs). A group of neurons immunoreactive (ir) to GnRH1 were identified along the ventral region of the olfactory bulb (vOB) in the telencephalon (vTel) and in the main areas of the diencephalon (especially the medial basal hypothalamus, HBM), including fibers extending into the pituitary gland. In contrast, GnRH2 neurons were confined to the midbrain tegmentum, close to the ventricular surface, without projections to the pituitary gland. Moreover, a cfGAP (GnRH1)-specific band (9 kDa) was identified in the brain and pituitary gland, while a cGAP-II (GnRH2)-specific band (26 kDa) was observed only in the brain extract. During the reproductive cycle, GnRH1-ir presented greater OD values at the vitellogenic and regression stages than at the previtellogenic stage and after artificially induced to spawn. Larger GnRH2-ir neurons were observed during the reproductive cycle, but a higher OD was identified only in the regression stage compared with the other maturation stages. Finally, GnRH1 axons were found to be directed towards the pituitary, and this GnRH type, which is probably the hypophysiotropic form, can contribute to the reproductive dysfunction that occurs in S. parahybae females in captivity, whereas GnRH2 may act as a neuromodulator and/or neurotransmitter.

Can estrogens be considered as key elements of the challenge hypothesis? The case of intrasexual aggression in a cichlid fish.

Territorial aggression has been widely studied in males and it has been historically suggested that androgens are key mediators of this behavior. However, more recent evidence suggests that it is the aromatization to estrogens, rather than androgens themselves, that is key to regulating this behavior. Females also display aggressive behaviors, but the physiological regulation of female aggression is still understudied when compared to males. In this context, the challenge hypothesis postulates that male-male aggressive interactions stimulate the production of androgens in males in periods of social instability. Here we determine plasma sex steroid levels in Cichlasoma dimerus to assess whether estrogens are related to aggressive behavior and to test the challenge hypothesis in both males and females. We set-up challenge trials as intrasexual dyadic encounters and determined androgen and estrogen levels before and after the trial in both winners and losers. Even though there were no differences in initial estradiol-17ß plasma levels between male winners and losers, initial levels were higher (p = .046) in female winners than in losers, while there were no differences in testosterone or 11-ketotestosterone levels. After trials, both males and females showed elevated levels of estradiol-17ß and both androgens, but only males exhibited a significant 1.45, 5.42 and 3.2-fold increase in estradiol-17ß, testosterone and 11-ketotestosterone, respectively (p = .023, p = .016, p = .018). Moreover, changes in circulating levels of estradiol-17ß in females after the trials do not depend on their reproductive status or on the outcome of the contest. We suggest that female aggression is associated with initial levels of estradiol-17ß, and that the challenge hypothesis, originally defined for androgens, could also be extended to estrogens.

Fighting cichlids: Dynamic of intrasexual aggression in dyadic agonistic encounters.

Aggression is an extremely complex behaviour and female aggression is understudied when compared to males. Despite the fact that it has been suggested that conflict among females may be more frequently resolved peacefully, in many species females show high levels of aggression. We used Cichlasoma dimerus to describe dynamics and conflict outcome in intrasexual agonistic encounters. We performed encounters of two sex-matched animals in a neutral arena and we recorded agonistic interactions during one hour. All aggressive and submissive behaviours were described and quantified to perform the ethogram. Encounters followed three phases: pre-contest, contest and post-resolution. Latency, time of resolution and frequency of aggressive displays did not differ between sexes. Relative variations in size between female opponents better explained aggression outcome in each contest, since higher levels of aggression occurred in dyads of more similar fish. However, this was not observed in males, suggesting that probably morphological characteristics could be less relevant in male conflict resolution. Altogether these results suggest that in this ethological context, C. dimerus females are as aggressive as males and that they have similar motivation towards territorial aggression, emphasizing the need of deepening the study of aggression in females and not only in males.

A game of two? Gene expression analysis of brain (cyp19a1b) and gonadal (cyp19a1a) aromatase in females of a Neotropical cichlid fish through the parental care period and removal of the offspring.

For many species parental behavior is essential for the survival of the offspring. While the ultimate causes of teleost parental behavior have been widely studied, comparatively little is known about its proximate causes. The aim of this study was to analyze the yet unexplored, potential dual role of brain and gonadal aromatases, the enzymes responsible for the conversion of androgens to estrogens in the brains and gonads of teleosts, respectively, on the different stages of the maternal care period of the biparental cichlid Cichlasoma dimerus, locally known as chanchita. By immunohistochemistry we analyzed the neural distribution of brain aromatase and observed it exclusively within the forebrain, including areas involved in the regulation of parental behavior. We next analyzed the gene expression of brain aromatase in the brain, and gonadal aromatase in the ovary, of female chanchitas through the parental care period. To further characterize the physiological environment associated to maternal care, we also evaluated sex steroid levels (17ß-estradiol, testosterone and 11-ketotestoterone) and ovarian follicle percentage. The onset of parental behavior specifically downregulated sex steroids synthesis and the rate of ovarian maturation, as denoted by a more than 10-fold decrease in steroid levels and delayed detection of mature follicles in females with offspring, compared to females which eggs were removed. Gene expression levels of both aromatases were independent of maternal care at the evaluated time points, even though they varied during the parental care period.

From molecule to behavior: Brain aromatase (cyp19a1b) characterization, expression analysis and its relation with social status and male agonistic behavior in a Neotropical cichlid fish.

The enzyme aromatase, responsible for the conversion of C19 androgens to C18 estrogens, exists as two paralogue copies in teleost fish: Cyp19a1a mostly expressed in the gonads, referred as gonadal aromatase, and Cyp19a1b, mostly expressed in the brain, accordingly known as brain aromatase. The neural localization of Cyp19a1b is greatly contained within the social behavior network and mesolimbic reward system in fish, suggesting a strong role of estrogen synthesis in the regulation of social behavior. In this work we aimed to analyze the variation in cyp19a1b expression in brain and pituitary of males of a highly social cichlid, Cichlasoma dimerus (locally known as chanchita), and its relation with inter-individual variability in agonistic behavior in a communal social environment. We first characterized chanchita's cyp19a1b mRNA and deduced amino acid sequence, which showed a high degree of conservation when compared to other teleost brain aromatase sequences, and its tissue expression patterns. Within the brain, Cyp19a1b was solely detected at putative radial glial cells of the forebrain, close to the brain ventricles. We then studied the relative expression levels of cyp19a1b by Real Time PCR in the brain and pituitary of males of different social status, territorial vs. non-territorial, and its relationship with an index of agonistic behavior. We found that even though, brain aromatase expression did not differ between types of males, pituitary cyp19a1b expression levels positively correlated with the index of agonistic behavior. This suggests a novel role of the pituitary in the regulation of social behavior by local estrogen synthesis.

Topological and histological description of preoptic area and hypothalamus in cardinal tetra Paracheirodon axelrodi (Characiformes: Characidae)

Topological and histological descriptions of the preoptic area and hypothalamus of the cardinal tetra Paracheirodon axelrodi were performed. Standard histological paraffin sections were used and stained with Nissl technique, and plastic sections for high-resolution optic microscopy (HROM). The preoptic area showed some differences related to the location of the magnocellular preoptic nucleus (PM) and the size of the neurons in this region, as they were the biggest in all the preoptic area. Additionally, within the preoptic area, the different structures that comprise the organum vasculosum of the lamina terminalis (OVLT) were identified and characterized. The hypothalamus could be subdivided in three regions - the ventral, the dorsal and the caudal hypothalamic regions - neuron morphology, size and staining pattern were similar in all of them.(AU)

ESUMEN Se realizó la descripción topológica e histológica del área preóptica e hipotálamo en el Neón cardenal Paracheirodon axelrodi. Se usaron cortes obtenidos con tecnicas histológicas estándar, coloreados con técnica de Nissl y secciones en resina con microscopía óptica de alta resolución (MOAR). El área preóptica muestra algunas diferencias relacionadas con la localización del núcleo preóptico magnocelular (PM) y el tamaño de algunas neuronas en esta región, puesto que estas eran las más grandes de toda el área preoptica. Adicionalmente, dentro del área preóptica, fue posible identificar y caracterizar las diferentes estructuras que componen el órgano vasculoso de la lámina media (OVLM). El hipotálamo puede sudividirse en tres zonas: la zona hipotalámica ventral, la zona hipotalámica dorsal y la zona hipotalámica caudal. La morfología de las neuronas de los núcleos que comprenden las diferentes zonas del hipotálamo tiene tamaño, forma y coloración similar.(AU)

The pineal complex: a morphological and immunohistochemical comparison between a tropical (Paracheirodon axelrodi) and a subtropical (Aphyocharax anisitsi) characid species.

Cardinal neon Paracheirodon axelrodi and bloodfin tetra Aphyocharax anisitsi are two species of characids with high trade value as ornamental fish in South America. Although both species inhabit middle water layers, cardinal neon exhibits a tropical distribution and bloodfin tetra a subtropical one. In this work, we carried out an anatomical, histological and immunohistochemical study of the pineal complex of P. axelrodi and A. anisitsi. In both species, the pineal complex consisted of three components, the pineal and parapineal organs and the dorsal sac (DS). The pineal organ was composed of a short, thin pineal stalk (PS), vertically disposed with respect to the upper surface of the telencephalon, and a pineal vesicle (PV), located at the distal end of the PS and attached to the skull by connective tissue. The pineal window (PW), a site in the skull where the luminal information accesses the pineal organ, appeared just above the latter structures. In the epidermis of P. axelrodi's PW, club cells were identified, but were not observed in the epidermis of A. anisitsi's one. With respect to the DS, it appeared to be folded on itself, and was bigger and more folded in A. anisitsi than in P. axelrodi. Immunohistochemical assays revealed the presence of cone opsin-like and rod opsin-like photoreceptor cells in the PS and PV. These results provide a first insight into the morphological assembly of the pineal complex of both species, and contribute to a better understanding of the integration and transduction of light stimuli in characids. J. Morphol. 277:1355-1367, 2016. © 2016 Wiley Periodicals, Inc.

A case of intersex occurrence in Steindachneridion parahybae (Steindachner, 1877) (Siluriformes: Pimelodidae) under captivity condition: a cytogenetic and morphological study

Little is known about reproductive biology of endangered Steindachneridion parahybae , a gonochoristic teleost species inhabiting the Paraíba do Sul River Basin, and herein is the first description of intersex in S. parahybae juvenile. The normal appearance of ovaries and testes in juvenile from the same lot of breeding were also described for comparison, even as cytogenetic analysis was performed in these juveniles. One specimen was a priori classified as female due to the macroscopic characteristic of ovaries, with small yellow oocytes, without fringes (a main characteristic of catfish male), and larger than testes; however the microscopic analysis revealed the presence of ovotestes, including the complete spermatogenesis. S. parahybae had diploid number, 2n = 56 chromosomes with no evidence of differentiated sex chromosomes or supernumerary chromosomes among them. These findings may be due to the result of exposure to endocrine disrupting compounds or may also be influenced by environmental conditions. The possibility of intersexes might also happen spontaneously and it cannot be ruled out. Therefore, the functional significance and reproductive consequences of this anomaly remain to be determined, suggesting that this species may be susceptible to endocrine disruption. These results contribute to gain expertise about reproductive biology of an endangered species in captivity.(AU)

Poco se sabe sobre la biología reproductiva de Steindachneridion parahybae , una especie de teleósteo gonocorístico en peligro de extinción que habita la cuenca del río Paraíba do Sul y en éste trabajo se describe por primera vez la aparición de individuo intersexo en juvenil de S. parahybae . También se describió el aspecto normal de los ovarios y de los testículos de individuos juveniles procedentes del mismo lote de cría para su comparación; se realizó además el análisis citogenético. Un espécimen fue clasificado a priori como hembra debido a las características macroscópicas de los ovarios, con pequeños oocitos amarillos, sin flecos (característica principal de los bagres macho) y más grande que los testículos; sin embargo el análisis microscópico reveló la presencia de un ovotestis, incluyendo una espermatogénesis completa. S. parahybae presentó un número diploide, 2n = 56 cromosomas, sin evidencia de cromosomas sexuales diferenciados o supernumerarios entre ellos. Estos hallazgos pueden deberse al resultado de la exposición de los individuos a desorganizadores endocrinos o estar influenciados por las condiciones ambientales. Sin embargo no se puede descartar la posibilidad de la presencia de intersexos de forma espontánea. Por lo tanto, la importancia funcional y las consecuencias reproductivas de estas anomalías permanecen aún sin ser determinadas, sugiriendo que esta especie puede ser susceptible a los disruptores endocrinos. Estos resultados contribuyen a ampliar el conocimiento de la biología reproductiva de esta especie en peligro de extinción en condiciones de cautiverio.(AU)

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.

Gross anatomy and histology of the alimentary system of Characidae (Teleostei: Ostariophysi: Characiformes) and potential phylogenetic information

A compared study of the morphology of the alimentary tract and liver of seven selected species corresponding to the main clades of the Characidae family is presented herein. Three new set of characters corresponding to 1) alimentary tract gross anatomy, 2) alimentary tract histology and 3) liver gross anatomy are evaluated as potential sources of data for future phylogenetic studies of the Characidae. Not considerable interspecific variation was observed at the histological level and therefore this source is not considered to be phylogenetically informative at the taxonomic level analyzed. In contrast, liver and alimentary tract gross anatomy presented important interspecific variation while a relatively homogenous intraspecific morphology was observed. Those characters are optimized in tree-topologies from previous phylogenetic analyses and their evolution and potential relationship with ecological traits are discussed.

Un estudio comparado de la morfología del tracto alimentario y el hígado de siete especies seleccionadas correspondientes a los principales clados de la familia Characidae es presentada aquí. Tres nuevos conjuntos de caracteres correspondientes a 1) anatomía gruesa del tracto alimentario, 2) histología del tracto alimentario y 3) anatomía gruesa del hígado son evaluados aquí como potenciales fuentes de información para futuros estudios filogenéticos de los Characidae. No se observó una variación intraespecífica considerable a nivel histológico y consecuentemente esta fuente no es considerada como informativa filogenéticamente al nivel taxonómico analizado. En contraste, la anatomía gruesa del hígado y el tracto alimentario presentaron una variación interespecífica importante mientras que una relativamente homogénea variación intraespecífica fue observada. Estos caracteres son optimizados en topologías de árboles de análisis filogenéticos previos y su evolución y potencial relación con características ecológicas son discutidas.

Gonadotropins and Growth Hormone Family Characterization in an Endangered Siluriform Species, Steindachneridion parahybae (Pimelodidae): Relationship With Annual Reproductive Cycle and Induced Spawning in Captivity.

The aim of this study was to identify and characterize pituitary cells of Steindachneridion parahybae females in captivity, highlighting the possible relationship with reproductive disorders at this level, since this species shows oocyte final maturation, ovulation and spawning dysfunction in captivity. The localization and distribution of growth hormone (GH), prolactin (PRL), somatolactin (SL), ß-luteinizing hormone (ß-LH), and ß-follicle stimulating hormone (ß-FSH) immunoreactive (-ir) cells in the adenohypophysis was studied by immunohistochemical and Western blot methods. In addition, cellular morphometric analyses and semi-quantification of ir-cells optical density (OD) during the annual reproductive cycle and after artificial induced spawning (AIS) were performed. Results showed that the distribution and general localization of pituitary cell types were similar to that of other teleost species. However, the morphometrical study of adenohypophysial cells showed differences along the reproductive cycle and following AIS. In general, females at the vitellogenic stage presented greater OD values for GH, PRL and SL than at other maturation stages (previtellogenic and regression stages), probably indicating an increased cellular activity during this stage. Conversely, ß-LH OD did not vary during the annual reproductive cycle. After AIS, ß-LH, SL and GH ir-cells showed an increase in OD values suggesting a possible involvement on oocyte final maturation, ovulation and spawning or a feedback control on the brain-pituitary-gonads axis. Reproductive dysfunction in S. parahybae females in captivity may be due to alteration of the synthesis pathways of ß-LH. In addition, GH family of hormones could modulate associated mechanisms that influence the reproductive status in this species.