Hidden Diversity in Eigenmannia (Gymnotiformes: Sternopygidae) Populations from Upper Paraná and Paraguay Rivers.

Eigenmannia is a highly diverse genus within the Sternopygidae family, comprising 30 species. Due to its complex taxonomy, molecular analyses have been crucial for species delimitation within this group. Therefore, the present study presents a genetic analysis using sequences of the mitochondrial gene cytochrome c oxidase subunit 1 (COI) in specimens previously identified through alpha taxonomy as E. correntes (with unpublished data), E. virescens, and E. trilineata, originating from various locations within the Upper Paraná and Paraguay River basins in Brazil. The molecular data confirm the taxonomic complexity of the genus, as individuals morphologically identified as E. virescens and E. trilineata shared the same haplotype (H52). Furthermore, the results of the species delimitation tests suggest that specimens morphologically identified as E. virescens belong to the species E. trilineata. In addition, samples morphologically identified as E. correntes may correspond to more than one Operational Taxonomic Units (OTUs). Furthermore, the intraspecific Kimura-2-parameter (K2P) distances within the different studied populations are significant. This study has contributed valuable information about genetic diversity in Eigenmannia, emphasizing the importance of using integrative analyses to resolve taxonomic conflicts within the group. It also supports biogeographical studies and assists in biodiversity conservation efforts.

Vasotocin but not isotocin is involved in the emergence of the dominant-subordinate status in males of the weakly electric fish, Gymnotus omarorum.

The establishment of the dominant-subordinate status implies a clear behavioral asymmetry between contenders that arises immediately after the resolution of the agonistic encounter and persists during the maintenance of stable dominance hierarchies. Changes in the activity of the brain social behavior network (SBN) are postulated to be responsible for the establishment and maintenance of the dominant-subordinate status. The hypothalamic nonapeptides of the vasopressin (AVP) and oxytocin (OT) families are known to modulate the activity of the SBN in a context-dependent manner across vertebrates, including status-dependent modulations. We searched for status-dependent asymmetries in AVP-like (vasotocin, AVT) and OT-like (isotocin, IT) cell number and activation immediately after the establishment of dominance in males of the weakly electric fish, Gymnotus omarorum, which displays the best understood example of non-breeding territorial aggression among teleosts. We used immunolabeling (FOS, AVT, and IT) of preoptic area (POA) neurons after dyadic agonistic encounters. This study is among the first to show in teleosts that AVT, but not IT, is involved in the establishment of the dominant-subordinate status. We also found status-dependent subregion-specific changes of AVT cell number and activation. These results confirm the involvement of AVT in the establishment of dominance and support the speculation that AVT is released from dominants' AVT neurons.

Neuroethology in South America: past, present and future.

South America is a vast continent endowed with extraordinary biodiversity that offers abundant opportunities for neuroethological research. Although neuroethology is still emerging in the region, the number of research groups studying South American species to unveil the neural organization of natural behaviors has grown considerably during the last decade. In this Perspective, we provide an account of the roots and strategies that led to the present state of neuroethology in the Southern Cone of America, with a forward-looking vision of its role in education and its international recognition. Hopefully, our Perspective will serve to further promote the study of natural behaviors across South America, as well as in other scarcely explored regions of the world.

Karyotype description and comparative chromosomal mapping of rDNA and U2 snDNA sequences in Eigenmannialimbata and E.microstoma (Teleostei, Gymnotiformes, Sternopygidae).

The genus Eigenmannia Jordan et Evermann,1896 includes electric fishes endemic to the Neotropical region with extensive karyotype variability and occurrence of different sex chromosome systems, however, cytogenetic studies within this group are restricted to few species. Here, we describe the karyotypes of Eigenmannialimbata (Schreiner et Miranda Ribeiro, 1903) and E.microstoma (Reinhardt, 1852) and the chromosomal locations of 5S and 18S rDNAs (ribosomal RNA genes) and U2 snDNA (small nuclear RNA gene). Among them, 18S rDNA sites were situated in only one chromosomal pair in both species, and co-localized with 5S rDNA in E.microstoma. On the other hand, 5S rDNA and U2 snRNA sites were observed on several chromosomes, with variation in the number of sites between species under study. These two repetitive DNAs were observed co-localized in one chromosomal pair in E.limbata and in four pairs in E.microstoma. Our study shows a new case of association of these two types of repetitive DNA in the genome of Gymnotiformes.

Comparative bioaccumulation of PAH and BTEX in Malapterurus electricus (Siluriformes: Malapteruridae) and its enteric parasite, Electrotaenia malopteruri Sampled from Lekki lagoon, Lagos, Nigeria / Bioacumulação comparativa de HAP e BTEX em Malapterurus electricus (Siluriformes: Malapteruridae) e seu parasita entérico, Electrotaenia malopteruri, coletado na lagoa Lekki, Lagos, Nigéria

Contamination of Lekki lagoon by petrogenic chemicals such as polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylene (BTEX) has been widely reported. The study was aimed at investigating the bioaccumulation of PAH and BTEX in Malapterurus electricus collected from Lekki lagoon in Lagos, Nigeria. BTEX was analyzed in the intestine, water, and sediment samples using 8260B Agilent 7890B gas chromatograph coupled to a mass spectrometer (GC-MS). While PAHs were tested in the same media using a gas chromatograph coupled to a flame ionization detector (GC-FID). Histopathological analysis of the fish intestine was conducted using haematoxylin and eosin (H&E) stains. Parasite intensity, antioxidant enzymes, and lipid peroxidation activities were investigated in the fish. The parasitic infection detected in Malapterurus electricus was Electrotaenia malopteruri. The parasite showed weak and no depurative capacities for BTEX and PAH respectively. The decrease in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) in conjunction with an increase in Malondialdehyde (MDA) characterized relatively higher susceptibility among the male fish. Varieties of tissue injuries increased with the standard length of the fish groups. Results suggest that lengthier and uninfected M. electricus were more susceptible to PAH in Lekki lagoon than the shorter and infected ones. The study demonstrated a promising tendency of the enteric parasite, E. malopteruri to depurate chlorobenzene, ethylbenzene, o-xylene, m+p-xylene, and 1,4-dichlorobenzene from the intestine of its host fish, M. electricus, while PAHs were poorly mediated by the parasite.(AU)

A contaminação da lagoa Lekki por produtos químicos petrogênicos, como hidrocarbonetos aromáticos policíclicos (HAP) e benzeno, tolueno, etilbenzeno e xileno (BTEX), foi amplamente relatada. O estudo teve como objetivo investigar a bioacumulação de HAP e BTEX em Malapterurus electricus, coletados na lagoa Lekki, em Lagos, Nigéria. O BTEX foi analisado no intestino, na água e nas amostras de sedimento usando o cromatógrafo de gás Agilent 7890B 8260B acoplado a um espectrômetro de massa (GC-MS). Já os HAP foram testados no mesmo meio utilizando cromatógrafo gasoso acoplado a detector de ionização de chama (GC-FID). A análise histopatológica do intestino do peixe foi conduzida usando colorações de hematoxilina e eosina (H&E). Intensidade de parasitas, enzimas antioxidantes e atividades de peroxidação lipídica foram investigadas nos peixes. A infecção parasitária detectada em Malapterurus electricus foi Electrotaenia malopteruri. O parasita mostrou fraca e nenhuma capacidade depurativa para BTEX e HAP, respectivamente. A diminuição da superóxido dismutase (SOD), catalase (CAT) e glutationa reduzida (GSH), em conjunto com o aumento do Malondialdeído (MDA), caracterizou a suscetibilidade relativamente maior entre os peixes machos. Variedades de lesões nos tecidos aumentaram com o comprimento padrão dos grupos de peixes. Os resultados sugerem que os M. electricus maiores e não infectados foram mais suscetíveis aos HAP na lagoa Lekki do que os menores e infectados. O estudo demonstrou uma tendência promissora do parasita entérico E. malopteruri de depurar clorobenzeno, etilbenzeno, o-xileno, m + p-xileno e 1,4-diclorobenzeno do intestino de seu peixe hospedeiro, M. electricus, enquanto os HAP foram mal mediados pelo parasita.(AU)

Comparative Bioaccumulation of PAH and BTEX in Malapterurus electricus (Siluriformes: Malapteruridae) and its Enteric Parasite, Electrotaenia malopteruri Sampled from Lekki Lagoon, Lagos, Nigeria / Bioacumulação comparativa de HAP e BTEX em Malapterurus electricus (Siluriformes: Malapteruridae) e seu parasita entérico, Electrotaenia malopteruri, coletado na lagoa Lekki, Lagos, Nigéria

Abstract Contamination of Lekki lagoon by petrogenic chemicals such as polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylene (BTEX) has been widely reported. The study was aimed at investigating the bioaccumulation of PAH and BTEX in Malapterurus electricus collected from Lekki lagoon in Lagos, Nigeria. BTEX was analyzed in the intestine, water, and sediment samples using 8260B Agilent 7890B gas chromatograph coupled to a mass spectrometer (GC-MS). While PAHs were tested in the same media using a gas chromatograph coupled to a flame ionization detector (GC-FID). Histopathological analysis of the fish intestine was conducted using haematoxylin and eosin (H&E) stains. Parasite intensity, antioxidant enzymes, and lipid peroxidation activities were investigated in the fish. The parasitic infection detected in Malapterurus electricus was Electrotaenia malopteruri. The parasite showed weak and no depurative capacities for BTEX and PAH respectively. The decrease in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) in conjunction with an increase in Malondialdehyde (MDA) characterized relatively higher susceptibility among the male fish. Varieties of tissue injuries increased with the standard length of the fish groups. Results suggest that lengthier and uninfected M. electricus were more susceptible to PAH in Lekki lagoon than the shorter and infected ones. The study demonstrated a promising tendency of the enteric parasite, E. malopteruri to depurate chlorobenzene, ethylbenzene, o-xylene, m+p-xylene, and 1,4-dichlorobenzene from the intestine of its host fish, M. electricus, while PAHs were poorly mediated by the parasite.

Resumo A contaminação da lagoa Lekki por produtos químicos petrogênicos, como hidrocarbonetos aromáticos policíclicos (HAP) e benzeno, tolueno, etilbenzeno e xileno (BTEX), foi amplamente relatada. O estudo teve como objetivo investigar a bioacumulação de HAP e BTEX em Malapterurus electricus, coletados na lagoa Lekki, em Lagos, Nigéria. O BTEX foi analisado no intestino, na água e nas amostras de sedimento usando o cromatógrafo de gás Agilent 7890B 8260B acoplado a um espectrômetro de massa (GC-MS). Já os HAP foram testados no mesmo meio utilizando cromatógrafo gasoso acoplado a detector de ionização de chama (GC-FID). A análise histopatológica do intestino do peixe foi conduzida usando colorações de hematoxilina e eosina (H&E). Intensidade de parasitas, enzimas antioxidantes e atividades de peroxidação lipídica foram investigadas nos peixes. A infecção parasitária detectada em Malapterurus electricus foi Electrotaenia malopteruri. O parasita mostrou fraca e nenhuma capacidade depurativa para BTEX e HAP, respectivamente. A diminuição da superóxido dismutase (SOD), catalase (CAT) e glutationa reduzida (GSH), em conjunto com o aumento do Malondialdeído (MDA), caracterizou a suscetibilidade relativamente maior entre os peixes machos. Variedades de lesões nos tecidos aumentaram com o comprimento padrão dos grupos de peixes. Os resultados sugerem que os M. electricus maiores e não infectados foram mais suscetíveis aos HAP na lagoa Lekki do que os menores e infectados. O estudo demonstrou uma tendência promissora do parasita entérico E. malopteruri de depurar clorobenzeno, etilbenzeno, o-xileno, m + p-xileno e 1,4-diclorobenzeno do intestino de seu peixe hospedeiro, M. electricus, enquanto os HAP foram mal mediados pelo parasita.

Neuroendocrine Mechanisms Underlying Non-breeding Aggression: Common Strategies Between Birds and Fish.

Aggression is an adaptive behavior that plays an important role in gaining access to limited resources. Aggression may occur uncoupled from reproduction, thus offering a valuable context to further understand its neural and hormonal regulation. This review focuses on the contributions from song sparrows (Melospiza melodia) and the weakly electric banded knifefish (Gymnotus omarorum). Together, these models offer clues about the underlying mechanisms of non-breeding aggression, especially the potential roles of neuropeptide Y (NPY) and brain-derived estrogens. The orexigenic NPY is well-conserved between birds and teleost fish, increases in response to low food intake, and influences sex steroid synthesis. In non-breeding M. melodia, NPY increases in the social behavior network, and NPY-Y1 receptor expression is upregulated in response to a territorial challenge. In G. omarorum, NPY is upregulated in the preoptic area of dominant, but not subordinate, individuals. We hypothesize that NPY may signal a seasonal decrease in food availability and promote non-breeding aggression. In both animal models, non-breeding aggression is estrogen-dependent but gonad-independent. In non-breeding M. melodia, neurosteroid synthesis rapidly increases in response to a territorial challenge. In G. omarorum, brain aromatase is upregulated in dominant but not subordinate fish. In both species, the dramatic decrease in food availability in the non-breeding season may promote non-breeding aggression, via changes in NPY and/or neurosteroid signaling.

The captivating effect of electric organ discharges: species, sex and orientation are embedded in every single received image.

Some fish communicate using pulsatile, stereotyped electric organ discharges (EODs) that exhibit species- and sex-specific time courses. To ensure reproductive success, they must be able to discriminate conspecifics from sympatric species in the muddy waters they inhabit. We have previously shown that fish in both Gymnotus and Brachyhypopomus genera use the electric field lines as a tracking guide to approach conspecifics (electrotaxis). Here, we show that the social species Brachyhypopomus gauderio uses electrotaxis to arrive abreast a conspecific, coming from behind. Stimulus image analysis shows that, even in a uniform field, every single EOD causes an image in which the gradient and the local field time courses contain enough information to allow the fish to evaluate the conspecific sex, and to find the path to reach it. Using a forced-choice test, we show that sexually mature individuals orient themselves along a uniform field in the direction encoded by the time course characteristic of the opposite sex. This indicates that these fish use the stimulus image profile as a spatial guidance clue to find a mate. Embedding species, sex and orientation cues is a particular example of how species can encode multiple messages in the same self-generated communication signal carrier, allowing for other signal parameters (e.g. EOD timing) to carry additional, often circumstantial, messages. This 'multiple messages' EOD embedding approach expressed in this species is likely to be a common and successful strategy that is widespread across evolutionary lineages and among varied signaling modalities.

Glutamatergic control of a pattern-generating central nucleus in a gymnotiform fish.

The activity of central pattern-generating networks (CPGs) may change under the control exerted by various neurotransmitters and modulators to adapt its behavioral outputs to different environmental demands. Although the mechanisms underlying this control have been well established in invertebrates, most of their synaptic and cellular bases are not yet well understood in vertebrates. Gymnotus omarorum, a pulse-type gymnotiform electric fish, provides a well-suited vertebrate model to investigate these mechanisms. G. omarorum emits rhythmic and stereotyped electric organ discharges (EODs), which function in both perception and communication, under the command of an electromotor CPG. This nucleus is composed of electrotonically coupled intrinsic pacemaker cells, which pace the rhythm, and bulbospinal projecting relay cells that contribute to organize the pattern of the muscle-derived effector activation that produce the EOD. Descending influences target CPG neurons to produce adaptive behavioral electromotor responses to different environmental challenges. We used electrophysiological and pharmacological techniques in brainstem slices of G. omarorum to investigate the underpinnings of the fast transmitter control of its electromotor CPG. We demonstrate that pacemaker, but not relay cells, are endowed with ionotropic and metabotropic glutamate receptor subtypes. We also show that glutamatergic control of the CPG likely involves two types of synapses contacting pacemaker cells, one type containing both α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptors and the other one only-NMDA receptor. Fast neurotransmitter control of vertebrate CPGs seems to exploit the kinetics of the involved postsynaptic receptors to command different behavioral outputs. The prospect of common neural designs to control CPG activity in vertebrates is discussed.NEW & NOTEWORTHY Underpinnings of neuromodulation of central pattern-generating networks (CPG) have been well characterized in many species. The effects of fast neurotransmitter systems remain, however, poorly understood. This research uses in vitro electrophysiological and pharmacological techniques to show that the neurotransmitter control of a vertebrate CPG in gymnotiform fish involves the convergence of only-NMDA and AMPA-NMDA glutamatergic synapses onto neurons that pace the rhythm. These inputs may organize different behavioral outputs according to their distinct functional properties.

Distinct neuron phenotypes may serve object feature sensing in the electrosensory lobe of Gymnotus omarorum.

Early sensory relay circuits in the vertebrate medulla often adopt a cerebellum-like organization specialized for comparing primary afferent inputs with central expectations. These circuits usually have a dual output, carried by center ON and center OFF neurons responding in opposite ways to the same stimulus at the center of their receptive fields. Here, we show in the electrosensory lateral line lobe of Gymnotiform weakly electric fish that basilar pyramidal neurons, representing 'ON' cells, and non-basilar pyramidal neurons, representing 'OFF' cells, have different intrinsic electrophysiological properties. We used classical anatomical techniques and electrophysiological in vitro recordings to compare these neurons. Basilar neurons are silent at rest, have a high threshold to intracellular stimulation, delayed responses to steady-state depolarization and low pass responsiveness to membrane voltage variations. They respond to low-intensity depolarizing stimuli with large, isolated spikes. As stimulus intensity increases, the spikes are followed by a depolarizing after-potential from which phase-locked spikes often arise. Non-basilar neurons show a pacemaker-like spiking activity, smoothly modulated in frequency by slow variations of stimulus intensity. Spike-frequency adaptation provides a memory of their recent firing, facilitating non-basilar response to stimulus transients. Considering anatomical and functional dimensions, we conclude that basilar and non-basilar pyramidal neurons are clear-cut, different anatomo-functional phenotypes. We propose that, in addition to their role in contrast processing, basilar pyramidal neurons encode sustained global stimuli such as those elicited by large or distant objects while non-basilar pyramidal neurons respond to transient stimuli due to movement of objects with a textured surface.

A new species of sexually dimorphic and rheophilic ghost knifefish (Apteronotidae: Gymnotiformes) from the Amazon basin.

A new species of ghost knifefish, Apteronotus, is described from high-energy environments in the Rios Mapuera and Trombetas (at Cachoeira Porteira waterfalls), Brazil. X-ray microcomputed tomography (µCT scan) was used to access the internal anatomy of the type series. The new species is distinguished from all congeners by the anteriormost position of the anus, with its posterior margin extending less than one eye diameter beyond the vertical through the caudal limit of the posterior nostril, the low number of anal-fin rays (117-125) and the reduced number of branchiostegal rays (three). A series of modifications associated with secondary sexual dimorphism on the preorbital region of mature males are depicted and discussed. In addition, comments on homologies of the branchiostegal rays in Apteronotidae are provided.

Feeding ecology of electric eel Electrophorus varii (Gymnotiformes: Gymnotidae) in the Curiaú River Basin, Eastern Amazon

In this study, the composition of the diet and the feeding activity of Electrophorus varii were evaluated. The influence of ontogeny and seasonality in these feeding parameters was also examined. Fish were collected in the Curiaú River Basin, Amazon, Brazil, from March 2005 to February 2006, during the rainy (January-June) and dry (July-December) seasons. Diet composition was characterized based on the analysis of stomach contents and feeding dynamics was assessed based on the Stomach Fullness Index (IR) calculated using stomach weight. Stomach content and RI data were grouped into four-cm size classes (40-80, 80-120, 120-160, and 160-200) and two seasonal periods (rainy and dry). The influence of ontogeny and seasonality in the diet was investigated through PERMANOVA, and in the food dynamics through ANOVA. The analysis of stomach contents revealed that fish were the most consumed preys by electric eels, especially Callichthyidae and Cichlidae. Diet composition and RI values of electric eels were not influenced by ontogeny and seasonality. Electric eels are fish predators, regardless of size class and seasonal period.(AU)

Neste estudo foram avaliadas a composição da dieta e a atividade alimentar de Electrophorus varii. A influência da ontogenia e da sazonalidade nestes aspectos da alimentação dos poraquês também foi examinada. Os peixes foram coletados na Bacia do rio Curiaú, Amazônia, Brasil, no período de março de 2005 a fevereiro de 2006, abrangendo os períodos chuvoso (janeiro-junho) e o seco (julho-dezembro). A dieta foi avaliada por meio da análise dos conteúdos estomacais e a dinâmica alimentar por meio do Índice de Repleção Estomacal (RI) baseado nos dados de peso do estômago. Os dados do conteúdo estomacal e do RI foram agrupados em quatro classes de tamanho em cm (40-80, 80-120, 120-160 e 160-200) e dois períodos sazonais (chuvoso e seco). A influência da ontogenia e da sazonalidade na dieta foi investigada por meio da PERMANOVA, e na dinâmica alimentar por meio da ANOVA. A análise do conteúdo estomacal mostrou que os peixes foram as presas mais consumidas pelos poraquês, especialmente Callichthyidae e Cichlidae. A composição da dieta e os valores de RI dos poraquês não foram influenciadas pela ontogenia e pela sazonalidade. Os poraquês são predadores piscívoros, independente da classe de tamanho e do período sazonal.(AU)

Comparative Bioaccumulation of PAH and BTEX in Malapterurus electricus (Siluriformes: Malapteruridae) and its Enteric Parasite, Electrotaenia malopteruri Sampled from Lekki Lagoon, Lagos, Nigeria

Abstract Contamination of Lekki lagoon by petrogenic chemicals such as polycyclic aromatic hydrocarbons (PAH) and benzene, toluene, ethylbenzene, and xylene (BTEX) has been widely reported. The study was aimed at investigating the bioaccumulation of PAH and BTEX in Malapterurus electricus collected from Lekki lagoon in Lagos, Nigeria. BTEX was analyzed in the intestine, water, and sediment samples using 8260B Agilent 7890B gas chromatograph coupled to a mass spectrometer (GC-MS). While PAHs were tested in the same media using a gas chromatograph coupled to a flame ionization detector (GC-FID). Histopathological analysis of the fish intestine was conducted using haematoxylin and eosin (H&E) stains. Parasite intensity, antioxidant enzymes, and lipid peroxidation activities were investigated in the fish. The parasitic infection detected in Malapterurus electricus was Electrotaenia malopteruri. The parasite showed weak and no depurative capacities for BTEX and PAH respectively. The decrease in superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH) in conjunction with an increase in Malondialdehyde (MDA) characterized relatively higher susceptibility among the male fish. Varieties of tissue injuries increased with the standard length of the fish groups. Results suggest that lengthier and uninfected M. electricus were more susceptible to PAH in Lekki lagoon than the shorter and infected ones. The study demonstrated a promising tendency of the enteric parasite, E. malopteruri to depurate chlorobenzene, ethylbenzene, o-xylene, m+p-xylene, and 1,4-dichlorobenzene from the intestine of its host fish, M. electricus, while PAHs were poorly mediated by the parasite.

Resumo A contaminação da lagoa Lekki por produtos químicos petrogênicos, como hidrocarbonetos aromáticos policíclicos (HAP) e benzeno, tolueno, etilbenzeno e xileno (BTEX), foi amplamente relatada. O estudo teve como objetivo investigar a bioacumulação de HAP e BTEX em Malapterurus electricus, coletados na lagoa Lekki, em Lagos, Nigéria. O BTEX foi analisado no intestino, na água e nas amostras de sedimento usando o cromatógrafo de gás Agilent 7890B 8260B acoplado a um espectrômetro de massa (GC-MS). Já os HAP foram testados no mesmo meio utilizando cromatógrafo gasoso acoplado a detector de ionização de chama (GC-FID). A análise histopatológica do intestino do peixe foi conduzida usando colorações de hematoxilina e eosina (H&E). Intensidade de parasitas, enzimas antioxidantes e atividades de peroxidação lipídica foram investigadas nos peixes. A infecção parasitária detectada em Malapterurus electricus foi Electrotaenia malopteruri. O parasita mostrou fraca e nenhuma capacidade depurativa para BTEX e HAP, respectivamente. A diminuição da superóxido dismutase (SOD), catalase (CAT) e glutationa reduzida (GSH), em conjunto com o aumento do Malondialdeído (MDA), caracterizou a suscetibilidade relativamente maior entre os peixes machos. Variedades de lesões nos tecidos aumentaram com o comprimento padrão dos grupos de peixes. Os resultados sugerem que os M. electricus maiores e não infectados foram mais suscetíveis aos HAP na lagoa Lekki do que os menores e infectados. O estudo demonstrou uma tendência promissora do parasita entérico E. malopteruri de depurar clorobenzeno, etilbenzeno, o-xileno, m + p-xileno e 1,4-diclorobenzeno do intestino de seu peixe hospedeiro, M. electricus, enquanto os HAP foram mal mediados pelo parasita.

Feeding ecology of electric eel Electrophorus varii (Gymnotiformes: Gymnotidae) in the Curiaú River Basin, Eastern Amazon

In this study, the composition of the diet and the feeding activity of Electrophorus varii were evaluated. The influence of ontogeny and seasonality in these feeding parameters was also examined. Fish were collected in the Curiaú River Basin, Amazon, Brazil, from March 2005 to February 2006, during the rainy (January-June) and dry (July-December) seasons. Diet composition was characterized based on the analysis of stomach contents and feeding dynamics was assessed based on the Stomach Fullness Index (IR) calculated using stomach weight. Stomach content and RI data were grouped into four-cm size classes (40-80, 80-120, 120-160, and 160-200) and two seasonal periods (rainy and dry). The influence of ontogeny and seasonality in the diet was investigated through PERMANOVA, and in the food dynamics through ANOVA. The analysis of stomach contents revealed that fish were the most consumed preys by electric eels, especially Callichthyidae and Cichlidae. Diet composition and RI values of electric eels were not influenced by ontogeny and seasonality. Electric eels are fish predators, regardless of size class and seasonal period.(AU)

Neste estudo foram avaliadas a composição da dieta e a atividade alimentar de Electrophorus varii. A influência da ontogenia e da sazonalidade nestes aspectos da alimentação dos poraquês também foi examinada. Os peixes foram coletados na Bacia do rio Curiaú, Amazônia, Brasil, no período de março de 2005 a fevereiro de 2006, abrangendo os períodos chuvoso (janeiro-junho) e o seco (julho-dezembro). A dieta foi avaliada por meio da análise dos conteúdos estomacais e a dinâmica alimentar por meio do Índice de Repleção Estomacal (RI) baseado nos dados de peso do estômago. Os dados do conteúdo estomacal e do RI foram agrupados em quatro classes de tamanho em cm (40-80, 80-120, 120-160 e 160-200) e dois períodos sazonais (chuvoso e seco). A influência da ontogenia e da sazonalidade na dieta foi investigada por meio da PERMANOVA, e na dinâmica alimentar por meio da ANOVA. A análise do conteúdo estomacal mostrou que os peixes foram as presas mais consumidas pelos poraquês, especialmente Callichthyidae e Cichlidae. A composição da dieta e os valores de RI dos poraquês não foram influenciadas pela ontogenia e pela sazonalidade. Os poraquês são predadores piscívoros, independente da classe de tamanho e do período sazonal.(AU)

Sexual dimorphism in the electric knifefish, Gymnorhamphichthys rondoni (Rhamphichthyidae: Gymnotiformes) / Dimorfismo sexual no peixe elétrico, Gymnorhamphichthys rondoni (Rhamphichthyidae: Gymnotiformes)

Sexual dimorfism refers to morphological differences between males and females of a species. It may be a result of different selection pressures acting on either or both sexes and may occur in any sexually-reproducing dioecious species, including fishes. We analyzed 63 females and 63 adult males of Gymnorhamphichthys rondoni (Gymnotiformes) collected by us or deposited in museum collections. Sex was identified through abdominal dissection. We measured length from snout to posterior end of anal-fin, anal-fin length, distance from anus to anal-fin origin, distance from genital papilla to anal-fin origin, body width at beginning of anal-fin, and head length. Morphometric data submitted to a Principal Component Analysis (PCA) grouped males and females according to variables related to body size (along the first component) and to head length and body height along the second and third components. Females were larger than males, whereas males had proportionally larger heads and higher bodies than females. The urogenital papilla of males and females showed differences in shape, size and relative position on the body. The female papilla was elongated horizontally, larger than that of males, and was located on a vertical line below the eye, while the papilla of the males was vertically elongated and located on a vertical line below the operculum. To our knowledge, this is the first recorded case of sexual dimorphism in a species of Rhamphichthyidae, a condition that is now known in all the currently recognized families of Gymnotiformes.(AU)

Dimorfismo sexual é caracterizado por diferenças entre machos e fêmeas de uma espécie. Pode estar presente em qualquer ser vivo dioico que se reproduza sexualmente, inclusive peixes. Analisamos 63 fêmeas e 63 machos adultos de Gymnorhamphichthys rondoni (Gymnotiformes) coletados por nós ou obtidos em coleções. O sexo foi determinado por dissecção abdominal. Medimos o comprimento do focinho até o final da origem da nadadeira anal, comprimento da nadadeira anal, distância da papila genital até a origem da nadadeira anal, distância do ânus até a origem da nadadeira anal, altura do corpo e comprimento da cabeça. Dados morfométricos submetidos a uma Análise de Componentes Principais (PCA) agruparam machos e fêmeas de G. rondoni em função de variáveis relacionadas ao tamanho do corpo ao longo do primeiro componente, ao comprimento da cabeça e à altura do corpo ao longo do segundo e terceiro componentes. Fêmeas foram maiores que os machos, enquanto machos tiveram a cabeça proporcionalmente maior e o corpo mais alto que as fêmeas. A papila urogenital de machos e fêmeas diferiu no formato, tamanho e posição relativa no corpo. A papila das fêmeas foi alongada horizontalmente, maior que a dos machos e localizada na linha vertical abaixo do olho, enquanto que a papila dos machos foi alongada verticalmente e localizada na linha vertical abaixo do opérculo. Até onde sabemos, esse é o primeiro caso registrado de dimorfismo sexual em uma espécie de Rhamphichthyidae, uma condição que é agora conhecida para todas as famílias atualmente reconhecidas de Gymnotiformes.(AU)

Sexual dimorphism in the electric knifefish, Gymnorhamphichthys rondoni (Rhamphichthyidae: Gymnotiformes)

Sexual dimorfism refers to morphological differences between males and females of a species. It may be a result of different selection pressures acting on either or both sexes and may occur in any sexually-reproducing dioecious species, including fishes. We analyzed 63 females and 63 adult males of Gymnorhamphichthys rondoni (Gymnotiformes) collected by us or deposited in museum collections. Sex was identified through abdominal dissection. We measured length from snout to posterior end of anal-fin, anal-fin length, distance from anus to anal-fin origin, distance from genital papilla to anal-fin origin, body width at beginning of anal-fin, and head length. Morphometric data submitted to a Principal Component Analysis (PCA) grouped males and females according to variables related to body size (along the first component) and to head length and body height along the second and third components. Females were larger than males, whereas males had proportionally larger heads and higher bodies than females. The urogenital papilla of males and females showed differences in shape, size and relative position on the body. The female papilla was elongated horizontally, larger than that of males, and was located on a vertical line below the eye, while the papilla of the males was vertically elongated and located on a vertical line below the operculum. To our knowledge, this is the first recorded case of sexual dimorphism in a species of Rhamphichthyidae, a condition that is now known in all the currently recognized families of Gymnotiformes. (AU)

Preoptic Area Activation and Vasotocin Involvement in the Reproductive Behavior of a Weakly Pulse-Type Electric Fish, Brachyhypopomus gauderio.

Social behavior exhibits a wide diversity among vertebrates though it is controlled by a conserved neural network, the social behavior network (SBN). The activity of the SBN is shaped by hypothalamic nonapeptides of the vasopressin-oxytocin family. The weakly electric fish Brachyhypopomus gauderio emits social electrical signals during courtship. Three types of vasotocin (AVT) cells occur in the preoptic area (POA), one of the SBN nodes. In this study, we aimed to test if POA neurons of the nucleus preopticus ventricularis anterior (PPa) and posterior (PPp), and in particular AVT+ cells, were activated by social stimuli using a 2-day behavioral protocol. During the first night, male-female dyads were recorded to identify courting males. During the second night, these males were divided in two experimental conditions: isolated and social (male with a female). Both AVT cells and the cellular activation of the POA neurons (measured by FOS) were identified. We found that the PPa of social males showed more FOS+ cells than the PPa of isolated males, and that the PPa had more AVT+ cells in social males than in isolated males. The double-immunolabeling for AVT and FOS indicated the activation of AVT+ neurons. No significant differences in the activation of AVT+ cells were found between conditions, but a clear association was observed between the number of AVT+ cells and certain behavioral traits. In addition, a different activation of AVT+ cell-types was observed for social vs. isolated males. We conclude that the POA of B. gauderio exhibits changes induced by social stimuli in reproductive context, involving an increase in AVT production and a different profile activation among AVT+ cell populations.

Distinctive mechanisms underlie the emission of social electric signals of submission in Gymnotus omarorum.

South American weakly electric fish (order Gymnotiformes) rely on a highly conserved and relatively fixed electromotor circuit to produce species-specific electric organ discharges (EODs) and a variety of meaningful adaptive EOD modulations. The command for each EOD arises from a medullary pacemaker nucleus composed of electrotonically coupled intrinsic pacemaker and bulbospinal projecting relay cells. During agonistic encounters, Gymnotus omarorum signals submission by interrupting its EOD (offs) and emitting transient high-rate barrages of low-amplitude discharges (chirps). Previous studies in Gymnotiformes have shown that electric signal diversity is based on the segregation of descending synaptic inputs to pacemaker or relay cells and differential activation of the neurotransmitter receptors -for glutamate or γ-aminobutyric acid (GABA) - of these cells. Therefore, we tested whether GABAergic and glutamatergic inputs to pacemaker nucleus neurons are involved in the emission of submissive electric signals in G. omarorum We found that GABA applied to pacemaker cells evokes EOD interruptions that closely resemble natural offs. Although in other species chirping is probably due to glutamatergic suprathreshold depolarization of relay cells, here, application of glutamate to these cells was unable to replicate the emission of this submissive signal. Nevertheless, chirp-like discharges were emitted after the enhancement of excitability of relay cells by blocking an IA-type potassium current and, in some cases, by application of vasotocin, a status-dependent modulator peptide of G. omarorum agonistic behavior. Modulation of the electrophysiological properties of pacemaker nucleus neurons in Gymnotiformes emerges as a novel putative mechanism endowing electromotor networks with higher functional versatility.

Karyotypic Diversity and Evolutionary Trends in Neotropical Electric Fish of the Genus Gymnotus (Gymnotiformes: Gymnotidae).

Electric fish of the order Gymnotiformes are endemic to the Neotropical region, and their highest diversity is observed in the Amazon region. The family Gymnotidae, which consists of the genera Electrophorus and Gymnotus, is a natural group and is located at the base of the phylogeny of the order. Gymnotus is a widely distributed and specious genus with high karyotypic diversity, especially concerning to the diploid number and the locations of repetitive sequences. Our karyotyping results in five species of the family Gymnotidae (Gymnotus ucamara, Gymnotus cf. stenoleucus, Gymnotus cf. pedanopterus, Gymnotus mamiraua, and Gymnotus carapo "Maranhão") corroborate the proposal of plasticity of the diploid number in this group. Moreover, in this study, we propose that the 5S ribosomal DNA (rDNA) sequences were species-specific markers that act as a potential biogeographical marker for the genus. Besides, the sequence's location, particularly in G. mamiraua from Central Amazon, shows a close relationship with 5S of the Gymnotus species, with 54 chromosomes, from the Paraná-Paraguay basin in the Center-South of Brazil. Considering that the ancestral diploid number for Gymnotidae is 52 chromosomes, we also suggest that the trend in the family is toward a decrease in the chromosome number. However, the carapo clade stands out in this regard, with an increase and a decrease in chromosome number; this pattern may be reinforced with the ecologic behaviors and the geodispersal patterns of this clade.

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.