Three new species of the Eigenmannia trilineata species group (Gymnotiformes: Sternopygidae) from northwestern South America

Eigenmannia is one of the more taxonomically complex genera within the Gymnotiformes. Here we adopt an integrative taxonomic approach, combining osteology, COI gene sequences, and geometric morphometrics to describe three new species belonging to the E. trilineata species group from Colombian trans-Andean region. These new species increase the number of species in the E. trilineata complex to 18 and the number of species in the genus to 25. The distribution range of the E. trilineata species group is expanded to include parts of northwestern South America and southern Central America.(AU)

Eigenmannia es uno de los géneros taxonómicamente más complejos dentro de los Gymnotiformes. En este artículo adoptamos un enfoque taxonómico integrador, que combina osteología, secuencias del gene COI y morfometría geométrica, para describir tres nuevas especies que pertenecen al grupo de especies de E. trilineata de la región transandina de Colombia. Estas nuevas especies aumentan el número de especies en el complejo E. trilineata a 18 y el número de especies en el género a 25. El rango de distribución del grupo de especies de E. trilineata se ha expandido al noroeste de Sudamérica y el sur de América Central.(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)

A new and improved electric fish finder with resources for printed circuit board fabrication

We describe the circuit design, construction, and operation of a field-portable electric fish finder (an AC-coupled wide-band differential bio-amplifier with loudspeaker output). This device permits detection and monitoring of the electric organ discharges generated by neotropical gymnotiform fishes (as well as the mormyroid fishes of tropical Africa). Our design is modified from earlier versions to optimize detection performance and stability over a wider range of ambient water conductivity, including under conditions of extremely low conductivity (< ca. 10 μScm-1). Our new electric fish finder design also incorporates complete waterproofing and longer battery autonomy. We provide Gerber and Eagle files made with the electronic design automation software 'Autodesk Eagle' to allow researchers to order printed circuit boards directly from commercial manufacturers.(AU)

Nós descrevemos o projeto de circuitos eletrônicos e as instrucões para a construção e uso de um detector de peixes elétricos portátil (bio-amplificador diferencial de banda-larga com acoplamento AC). Este aparelho permite a detecção e o monitoramento das descargas de órgãos elétricos gerados por peixes neotropicais da ordem Gymnotiformes (assim como dos peixes mormirídeos da África Tropical). Nosso projeto é modificado a partir de versões anteriores para otimizar o desempenho e a estabilidade sob uma faixa de condutividades ambientais mais ampla, incluindo condições de condutividade extremamente baixa (< ca. 10 μScm-1). Nosso detector de peixes elétricos novo também foi otimizado a fim de proporcionar impermeabilização completa e vida longa para as baterias. Nós fornecemos arquivos 'Gerber' e 'Eagle' preparados com o software de automação de projeto eletrônico 'Autodesk Eagle' para permitir aos pesquisadores a possibilidade de efetuar encomendas de nossa placa de circuito impresso direitamente das empresas de fabricação.(AU)

Dieta do peixe elétrico Gymnorhamphichthys petiti Géry & Vu-Tân-Tuê, 1964 (Rhamphichthyidae), em riachos da bacia do Rio Teles Pires, Amozônia Meridional / Diet of the knifefish Gymnorhamphichthys petiti Géry & Vu-Tân-Tuê, 1964 (Rhamphichthyidae) in streams of Teles pires river basin, Southern Amazon

Gymnorhamphichthys petiti é uma espécie de peixe elétrico que habita o fundo arenoso de riachos da bacia do rio Teles Pires, no entanto pouco se sabe a respeito de sua biologia. O objetivo foi analisar a dieta de G. petiti. As coletas foram realizadas no município de Cláudia, Mato Grosso, na bacia do Rio Teles Pires. As amostragens ocorreram nos meses de julho de 2010 e em maio e junho de 2011, em riachos de 1ª e 2ª ordem. Utilizou-se os métodos de frequência de ocorrência e volume relativo para o cálculo do Índice Alimentar (I.A.%) de 43 exemplares. O comprimento padrão variou entre 47,17 e 120,49 mm e o peso entre 0,12 e 2,04 g. Os itens alimentares encontrados foram: Nematoda, Acari, Ephemeroptera, Plecoptera, Hemiptera, Coleoptera, Trichoptera, Diptera, fragmento de insetos, ovos de insetos, sementes e areia. O item alimentar (IAi) de maior importância na dieta foi Nematoda, em razão do seu maior volume relativo. No entanto, imaturos de insetos da ordem Trichoptera, habitantes do substrato de areia apareceram em maior frequência nos estômagos, diferindo dos resultados encontrados para outras espécies de Gymnorhamphichthys. Tais resultados confirmam que G. petiti tem forte dependência de itens alimentares relacionados ao substrato arenoso.

Gymnorhamphichthys petiti is a species of electric fish that inhabits the sandy bottom of streams of Teles Pires river basin, however, little is known about the biology of this fish. Here we aim to assess the diet of G. petiti and to evaluate the importance of items present in its diet. Samples were collected in the municipality of Claudia, Mato Grosso state. Data collection occurred in July 2010, and in May and June 2011, covering streches of 150 meters of streams of 1st and 2nd order. We used Frequency of Occurrence and Relative Volume to calculate the Feeding Index (I.A.%) for 43 specimens. The standard length ranged from 47.17 to 120.49 mm and weight ranged from 0.12 to 2.04 g. The food items found were: Nematoda, Acari, Ephemeroptera, Plecoptera, Hemiptera, Coleoptera, Trichoptera, Diptera, body parts of insects, insect eggs, seeds and sand. Nematoda was the most important food item, due to its high relative volume. Immature individuals of sand-dwelling Trichoptera, however, were the most frequent item in stomachs, differing from the results for other Gymnorhamphichthys spp. These results confirm the strong dependency of G. petiti on food items present in the sandy substrate of bottoms of streams.

Systematics and biogeography of Sternarchellini (Gymnotiformes: Apteronotidae): Diversification of electric fishes in large Amazonian rivers

The Sternarchellini (Gymnotiformes, Apteronotidae) is a clade of 10 electric fish species that inhabit deep river channels of the Amazon and Orinoco basins, attain moderate adult body sizes (15-50 cm TL), and have a predatory life style. Here we trace the evolutionary origin and diversification of Sternarchellini using standard phylogenetic and biogeographic procedures and a dataset of 70 morphological characters. The main results are: 1) the genus Sternarchella includes both species currently assigned to the genus Magosternarchus; and 2) neither of the multi-species assemblages of Sternarchellini in the Amazon and Orinoco basins are monophyletic. Historical biogeographic analysis suggests that sternarchelline evolution was linked to the large-scale river capture event that formed the modern Amazon and Orinoco basins, i.e. the Late Miocene rise of the Vaupes structural arch and concomitant breaching of the Purus structural arch. This event is hypothesized to have contributed to formation of the modern sternarchelline species, and to the formation of the modern basin-wide sternarchelline species assemblages. The results indicate that cladogenesis (speciation) and anagenesis (adaptive evolution) were decoupled processes in the evolution of Sternarchellini...

Sternarchellini (Gymnotiformes, Apteronotidae) é um clado de 10 espécies de peixes elétricos que habitam canais profundos de rios das bacias do Amazonas e Orinoco, que atingem um tamanho moderado quando adultos (15-50 cm CT), e possuem hábito predatório. Rastreamos a origem evolutiva e diversificação de Sternarchellini utilizando técnicas filogenéticas e biogeográficas padrões e um conjunto de dados de 70 caracteres morfológicos. Os principais resultados são: 1) o gênero Sternarchella inclui duas espécies atualmente atribuídas ao gênero Magosternarchus; e 2) as assembleias de multi-espécies de Sternarchellini nas bacias Amazônica e do Orinoco não formam grupos monofiléticos. A análise biogeográfica histórica sugere que a evolução do Sternarchellini esteve ligada ao evento de captura de rio de grande escala que formou as atuais bacias do Amazonas e Orinoco, i.e., o soerguimento do arco estrutural Vaupés no Mioceno Superior e o rompimento concomitante do arco estrutural Purus. É proposto que esse evento contribuiu para o surgimento das espécies atuais de Sternarchellini, e para a formação das assembleias modernas de espécies de Sternarchellini com ampla distribuição nas bacias. Os resultados indicam que cladogênese (especiação) e anagenêse (evolução adaptativa) foram processos desacoplados na evolução de Sternarchellini...

Effects of methylmercury on electric organ discharges in the weak electric fish Gymnotus sylvius

Methylmercury (MeHg) is present in the environment because of natural and anthropogenic causes. MeHg can reach the central nervous system (CNS) and cause neurological damage in humans and animals. Electric organ discharges (EODs) in the weak electric fish Gymnotus sylvius are produced by the electric organ and modulated by the CNS. These discharges are used for electrolocation and communication. The purpose of the present study was to investigate the effects of dietary MeHg exposure on EOD rate in G. sylvius. An oscilloscope was used to record the EOD rate. Two treatments were investigated: chronic MeHg administration (4 µg/kg MeHg every 2 days, with a total of nine dietary exposures to MeHg) and acute MeHg administration (a single dose of 20 µg/kg MeHg). The control data for both treatments were collected every 2 days for 18 days, with a total of nine sessions (day 1 until day 18). Data of fish exposed to MeHg were collected every 2 days, totaling nine sessions (day 19 until day 36). Chronic treatment significantly increased the EOD rate in G. sylvius (p < .05), especially with the final treatment (day 32 until day 36). Acute treatment resulted in an initial increase in the EOD rate, which was maintained midway through the experiment (day 26 until day 30; p < .05). The present study provides the first insights into the effects of MeHg on EODs in weak electric fish. The EOD rate is a novel response of the fish to MeHg administration.

Redescription and phylogenetic position of the enigmatic Neotropical electric fish Iracema caiana Triques (Gymnotiformes: Rhamphichthyidae) using x-ray computed tomography

We redescribe Iracema caiana, a monotypic genus of the gymnotiform electric fish family Rhamphichthyidae. Iracema is known only from the type series (holotype and three paratypes) collected from the rio Jauaperi, affluent to the rio Negro in the Amazon basin, and was never collected again. Previous morphological studies were limited to features of external morphology. To study the osteology of Iracema we examined two specimens of different sizes using high-resolution x-ray computed tomography, a non-invasive and non-destructive technique to visualize internal anatomical structures. We describe and illustrate the osteology of Iracema caiana, and present data on morphometrics and external morphology. Contrary to previous hypotheses we propose that Iracema is the sister group to Rhamphichthys based on four synapomorphies: intermuscular bones present in the adductor mandibulae, reticulated texture of opercles, fully ossified Baudelot's ligaments, and elongate scales above the lateral line in the posterior portion of the body.

Iracema caiana, um genêro monotípico de peixes elétricos Gymnotiformes da família Rhamphichthyidae, é aqui redescrito. Iracema é conhecido apenas da série-tipo (holótipo e três parátipos) coletado no rio Jauaperi, afluente do rio Negro na bacia amazônica, nunca sendo coletado novamente. Estudos morfológicos prévios de Iracema foram limitados somente à morfologia externa. Neste trabalho, a osteologia do gênero foi examinada com base em dois espécimes de diferentes tamanhos usando-se tomografia computadorizada de alta resolução, uma técnica não invasiva para a visualização de estruturas anatômicas internas. Caracteres externos e morfométricos são apresentados e a osteologia é ilustrada e descrita. Contrariamente a hipóteses prévias, Iracema é proposto como grupo irmão de Rhamphichthys com base em quatro sinapomorfias: presença de ossos intermusculares no adductor mandibulae, textura reticulada do opérculo, ligamento de Baudelot completamente ossificado e escamas alongadas na região posterior do corpo acima da linha lateral.

On Apteronotus magdalenensis (Miles, 1945) (Gymnotiformes: Apteronotidae): a poorly known species endemic to the río Magdalena basin, Colombia

Based on the examination of the two available paratypes and recently collected material, we present new data and information on the electric knifefish Apteronotus magdalenensis, a species endemic to the río Magdalena-Cauca basin in Colombia. Since Miles' description in 1945, this species was not collected until recent field work at the Torrents of Honda and additional localities. We present data on the external morphology, morphometrics, pigmentation and electric organ discharges (EODs), of A. magdalenensis. We also review its distribution, ecology and conservation status.

Basados en la revisión de los dos paratipos disponibles y material recientemente colectado, presentamos nuevos datos e informaciones del pez cuchillo eléctrico Apteronotus magdalenensis, una especie endémica de la cuenca del río Magdalena-Cauca en Colombia. Desde su descripción en 1945 por Miles, esta especie no fue colectada hasta trabajo de campo llevado a cabo recientemente en los rápidos de Honda y localidades adicionales. Presentamos datos sobre la morfología externa, morformetría, pigmentación y descarga del órgano eléctrico (EOD) de A. magdalenensis. También revisamos su distribución, ecología y estatus de conservación.

Reproductive biology of the Neotropical electric fish Brachyhypopomus draco (Teleostei: Hypopomidae) from southern Brazil

The reproductive biology of a population of the weakly electric fish Brachyhypopomus draco from southern Brazil is described. Information is provided on the establishment of the reproductive period in this species and its relations with environmental and feeding factors, as well as on the absolute and relative fecundities, spawning type, sex ratio and sexual dimorphism. The species exhibits a relatively long reproductive period, a relative fecundity of 0.173 oocytes per mg of female total weight, and fractional spawning. The sex ratio did not differ from 1:1 during all sampled months. Sexual dimorphism related to hypertrophy of the male's distal portion of caudal filament was observed and males grew to greater lengths than females. Male gonadosomatic index (GSI) was significantly related to water depth, oxygen saturation and temperature. Female GSI was significantly related to water depth and hepatosomatic index.(AU)

Descreve-se a biologia reprodutiva de uma população do peixe elétrico Brachyhypopomus draco do sul do Brasil. São apresentadas informações a respeito do período reprodutivo estabelecido e suas relações com fatores ambientais e alimentares, bem como a fecundidade absoluta e relativa, tipo de desova, proporção sexual e dimorfismo sexual. A espécie apresentou um período reprodutivo relativamente longo, uma fecundidade relativa de 0,173 ovócitos por mg de peso total da fêmea e uma desova do tipo parcelada. A proporção sexual encontrada foi de 1:1 durante todos os meses amostrados. Dimorfismo sexual relacionado com a hipertrofia da porção distal do filamento caudal dos machos e com o tamanho total dos espécimes - machos atingindo tamanhos maiores do que as fêmeas - foi encontrado. O IGS dos machos foi significativamente relacionado com a profundidade da água, a saturação de oxigênio e a temperatura; o IGS das fêmeas foi significativamente relacionado com a profundidade da água e o índice hepatossomático.(AU)

Design and construction of an Electric Fish Finder

We provide notes on the design and construction of an Electric Fish Finder - a portable differential amplifier for detecting the electrostatic fields of gymnotiform knifefishes. The device can be adapted to locate electric fishes in any kind of aquatic environment. It is rugged, water resistant, and powered by alkaline batteries. This contribution is part of a series of technical papers designed to encourage students of neotropical ichthyology to explore the ecology, systematics, and electric signaling of gymnotiform fishes

Nós fornecemos o esquema e as instruções para a construção de um Detector de Peixes Elétricos - um amplificador portátil de banda larga utilizado para detectar os campos elétricos de peixes gymnotiformes. Este aparelho pode ser adaptado para encontrar peixes elétricos em diversos ambientes aquáticos. É resistente, à prova d'água e energizado por baterias alcalinas. Esta contribuição faz parte de uma série de artigos técnicos que pretende encorajar estudantes de ictiologia neotropical a explorar a ecologia, sistemática e comunicação elétrica de peixes gymnotiformes

Avaliação da mutagênese e genotoxicidade em Eigenmannia virescens (Teleostei: Gymnotiformes) expostos ao benzeno / Avaliation of mutagenicity and gentotoxicity in Eigenmannia virescens (Teleostei: Gymnotiformes) exposed to benzene

Os efeitos de substâncias genotóxicas sobre o genoma de peixes tem sido objeto de muitos estudos, sobretudo daqueles que buscam estabelecer a resposta dos genes aos estímulos ambientais. O presente trabalho teve como objetivo realizar um estudo sobre mutagenicidade e genotoxicidade em peixes elétricos da espécie Eingenmannia virescens, pela exposição ao benzeno (50ppm), utilizando as técnicas da Freqüência de Micronúcleos (MNs) e o Ensaio do Cometa. Foram coletadas amostras do sangue de dez peixes em diferentes tempos de exposição: T0, 24h, 48h, 72h, 96h e 360h (15 dias). Para a análise das lâminas no Teste do MN, foram contadas 1.000 células e estipulada a freqüência de ocorrência de MNs. Para análise do Ensaio do Cometa a contagem foi feita estipulando quatro classes de danos: I - II - III - IV, e para a análise estatística foram atribuídos valores numéricos (ranques) de 0 a 3, respectivamente, verificando diferenças significativas para a soma dos ranques em todos os tempos de exposição em relação ao T0. No Teste do Micronúcleo não foi possível detectar efeitos mutagênicos significativos nos eritrócitos analisados. No entanto, para o Ensaio do Cometa os resultados sugerem ação genotóxica do benzeno, devido a um aumento gradual no número de células com maiores classes de danos de acordo com maior tempo de exposição, indicando um efeito tempo-dependente. Estes resultados sugerem maior sensibilidade do Ensaio do Cometa que o Teste do MN.

The effects of genotoxic substances on fishes genome have been object of many studies, especially those which attempt to establish the responses of genes to environmental stimulus. The objective of this study was to evaluate the mutagenicity and genotoxicity in electric fishes of species Eingenmannia virescens, under to benzene exposure (50ppm), utilizing Micronuclei Test (MNs) and Comet Assay techniques. Ten fish blood samples were collected in different times of exposure: T0, 24h, 48h, 72h, 96h and 360h (15 days). To determine the frequency of MNs, 1.000 cells per microscopical slides were counted. For the Comet Assay analysis, four damage classes were defined: I - II - III - IV, and for the statistic analysis number values (ranks) from 0 to 3 were assigned for each class. The sum of ranks (values) for all times of exposure was compared to T0 and these differences were statistically analyzed. On Micronuclei Test demonstrated do not possible detect significant mutagenic effects in the erythrocytes analyzed. On the other hand, for the Comet Assay, the results suggested genotoxic action of benzene, proper the gradual increase of number of cells with greatest damage class with the greatest of exposure time, indicating an effect time-dependent. These results suggested the most sensibility for the Comet Assay like Micronuclei Test.

Dimorfismo sexual em Siluriformes e Gymnotiformes (Ostariophysi) da Amazônia / Sexual dimorfism in Amazonian Siluriformes and Gymnotiformes (Ostariophysi)

No presente trabalho é feito um levantamento dos casos de dimorfismo sexual em Siluriformes e Gymnotiformes. Este levantamento se restringe às formas Neotropicais, com ênfase mais especificamente, às da Amazônia. Peixes dessa região possuem uma grande diversidade, ainda que os limites intraespecíficos não estejam bem definidos. Embora preliminar, o mapeamento de características dimórficas em um cladograma referente a família Loricariidae (Siluriformes) auxilia na demonstração de que padrões de dimorfismo sexual são consistentes com hipóteses de monofiletismo. Em Apteronotidae (Gymnotiformes), com base no mapeamento dos caracteres tamanho e forma do focinho e presença de dentes diferenciada em árvores filogenéticas, podemos inferir que esses caracteres originaram-se como eventos independentes em vários táxons. Recentemente, em Gymnotiformes, foram detectados casos de erros taxonômicos atribuídos a diferenças extremas entre machos e fêmeas.

Biochemical and hematological responses of the banded knife fish Gymnotus carapo (Linnaeus, 1758) exposed to environmental hypoxia

Oxygen of tropical freshwater environments fluctuates drastically. Eutrophic lakes and ponds of warm waters frequently reach very low oxygen concentrations. This is the most common habitat of the banded knife fish "tuvira" Gymnotus carapo. This electric fish is reported to present bimodal breathing to cope with low environmental oxygen. Biochemical responses can be also observed in fishes facing hypoxia but none were studied in tuvira. In the present study, haematological and metabolic changes were investigated in two groups of fish exposed to hypoxia for 1 and 3 hours. Haematocrit, red blood cells and haemoglobin concentration indicated erythrocyte release from hematopoietic organs and swelling of red blood cells. Glycogen, glucose, lactate, pyruvate, and amino acids were quantified in liver, kidney and white muscle. The metabolic profile of G. carapo to cope with hypoxia suggested liver gluconeogenesis probably supported by proteolysis. The kidney and liver presented the same biochemical trend suggesting similar metabolic role for both organs. Glucogenolysis followed by glucose fermentation and protein mobilisation was observed in the white muscle. The air breathing behaviour of tuvira works in parallel with metabolism to prevent damages from hypoxia. Metabolic adjustments are observed when the air taking is avoided

Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep

Technical problems have hampered the study of sleep in teleosts. The electrical discharges of Gymnotus carapo L. (Gymnotidae: Gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. The discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. G. carapo showed conspicuous signs of behavioral sleep. During these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (SDI) of the orienting reflex was investigated. All 20 animals monitored maintained electrical discharges during behavioral sleep. The discharge frequencies during sleep (50.3 Ý 10.4 Hz) were not significantly different from those observed when the fish was awake and inactive (57.2 Ý 12.1 Hz) (Wilcoxon matched-pairs signed-ranks test, P>0.05). However, the SDI, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. Additional observations showed that the species had cannibalistic habits. When presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. We conclude that the electrical discharges of G. carapo were not conspicuous indicators of behavioral sleep. Discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks

Aspectos bioecológicos de las taxocenosis de peces eléctricos o cuchillos (Ostariophysi: Gymnotiformes) en los Llanos de Apure: Venezuela / Bioecological aspects of the taxocenosis of electric fishes (Ostariophysi: Gymnotiformes) in the Apure: Llanos de Venezuela

Se estudia diferentes aspectos relativos a la diversidad, abundancia, distribución, espacio temporal, alimentación y reproducción de los peces Gymnotiformes, en dos sistemas (Caño Guarítico y áreas inundables periféricas) de los Llanos de Apure, Venezuela. Fueron identificadas 21 especies incluídas en 6 familias. El cauce principal del Caño Guarítico presentó una mayor diversidad de Gymnotiformes (19 sp.) en relación a las áreas inundables (12 sp.). El hábitat más característico fué el fondo del cauce y mostró el mayor número de especies (12 sp.). Eigenmannia virescens y Eigenmannia macrops fueron las especies más abundantes en el área inundable y Caño Guarítico, respectivamente. Le siguen en importancia Adontosternarchus devenanzii y Sternopygus macrurus. Las fases inmaduras de insectos acuáticos constituyen el principal alimento de casi todos los Gymnotiformes. La zooplanctivoría e ictiofagia aparece secundariamente. No se observaron diferencias estacionales importantes en la dieta de la mayoría de las especies, excepto en Gymnotus carapo y algunas especies zooplanctófagas secundarias. Todas las especies se reproducen durante las lluvias y aguas altas. La mayoría completan su ciclo de vida en las áreas inundables mientras que una minoría lo hace en el cauce principal

Molecular and immunocytogenetics of Brazilian fishes

Fish cytogenetics has incorporated during the last years new methodologies that employ molecular techniques, such as in situ hybridization with DNA probes for localization of chromosomal segments, chromosome banding using in situ digestion with restriction enzymes, in vivo incorporation of DNA base analogues, base-specific fluorochrome staining and, more recently, immunolabelling of chromosomes with antinucleoside antibodies. These techniques, associated with results obtained by using classical cytogenetic markers such as C-bands and nucleolus organizer regions, have allowed a more comprehensive understanding of the molecular structure of chromosomes and enlarged the area of cytogenetic evolutive studies. In neotropical fish the use of these modern techniques resulted in the localization of rDNA segments and the analysis of their activity; the localization of telomeric DNA segments; the identification of C-band modified patterns in species analyzed by in situ digestion of chromosomes with restriction endonucleases; the identification of R-handing patterns after incorporation of 5-bromodeoxyuridine; and, using the antibody antimethylcytosine, the identification of the methylated state of the heterochromatin in diploids and triploids.

Lectinas solubles beta-galactosídicas / Beta-galactoside solubles lectins

Sobre la base de estudios estructurales y funcionales, las lectinas animales se han clasificado en dos tipos: el Tipo C, caracterizado por su dependencia de los iones de calcio y el Tipo S que no es calciodependiente, sino tioldependiente. Entre estas últimas, se ha estudiado ampliamente el grupo de lectinas S-Lac, que son extraídas con buffers salinos con lactosa, en presencia de tioles. Contituyen una familia de proteínas realcionadas estructuralmente, que contienen una serie de aminoácidos conservados. Se unen específicamente a glicoconjugados complementarios y su biosíntesis y localización son reguladas por el desarrolo. Su rol puede relacionarse con diversas actividades biológicas que poderían variar según el órgano.

Effect of external carbon dioxide concentration on electric organ dischargge frequency by the gymnotiform fish Apteronotus albifrons

A model is described for the instantaneous frequency (F) of electric organ discharge in Apteronotus albifrons: F=H/(aH + b), where a and b are linear parameters and H, hydrogen ion concentration, pH from 7.10 to 4.89 was modified by increasing external carbon dioxide concentrations. With the increase in pH from 5.17 to 7.40, corresponding to a decrease of carbon dioxide concentration, the equation was as follows: F=(logH)/(a ,log H=b). The model search consisted of the adjustment of a simple linear regression using fucntion transformation for the most adequate residue analysis by the Durbin-Watson test. The parallelism was checked by comparing regression lines with homogeneous variances and using other tests for non-homogeneous variances

Calcium binding sites in the Discopyge tschudii electrocyte: physiological implications

Se investigó la presencia de sitios fijadores decalcio en la electroplaca del pez eléctrico Discopyge tschudii mediante el uso de fijadores, con alto contenido de calcio. Se encontraron sitios fijadores de calcio en el terminal sináptico y en el electrocito. En las vesículas sinápticas se observó la presencia de una partícula electrón densa de 25 nm de diámetro aproximadamente, calcio dependiente, en contacto con la membrana vesicular. En el electrocito se encontraron sitios fijadores de calcio de forma redondeada, de 50-60 nm de diámetro promedio, dispersos en el citplasma o unidos a las membranas celulares, especialmente la membrana plasmática ventral y las membranas del sistema canalicular dorsal. A nivel de la membrana plasmática ventral esos sitios estaban aislados o fusionaods formando una banda festoneada. En fijaciones sin calcio se observó la presencia de formaciones vesiculares y perfilkes omega, electrónicamente transparentes, en la misma localización. También se encontrron formaciones vesiculares en el citoplasma del electrocito. La frecuencia y densidad electrónica de los sitios fijadores de calcio del electrocito presentaban una gran variabilidad, sugerindo una correlación funcional. Se postula que esos sitios fijadores de calcio corresponden a vesículas endocitóticas, probablemente relacionadas con la internalización de complejos ligando receptor involucrados en el metabolismo del receptor o en la activación de alguna estructura funcional del electrocito, como el sistema canalicular dorsal. Un resumen de este trabajo fue presentado en la primera reunión de la Asociación Neuroquímica Argentina, realizada en Cóordoba, República Argentina, en noviembre 1986