Cellular patterning and cyto-architectural organization of the skin of electric catfish (Malapterurus electricus, Siluriformes) with a particular emphasis on its ampullary electroreceptor.

The functional morphology of the skin of Malapteruridae is presumably evolved to cope with a diversified range of ambient physiological, environmental, and behavioral conditions. Herein, we firstly characterized the microstructures and intriguing patterning of the skin of twelve adult electric catfish (Malapterurus electricus, Malapteruridae) using histological, histochemical, immunofluorescent, and ELISA standard methodology. The skin comprises three sequentially-oriented layers: the epidermis, dermis, and hypodermis with a significantly increased thickness of the former. The epidermis contains four types of cells: the surface epithelial cells, mucous cells, granular cells, and club cells. We defined distinctive ampullary electroreceptors in the outer epidermis that possess flask-shaped sensory crypt containing electroreceptor cells together with vertical collagen rods. Dermis and hypodermis are composed of connective tissue; however, the former is much more coarse and dense with comparable reactivity for Masson-Goldner trichrome (MT). Placing our data in the context of the limited body of previous work, we showed subtle changes in the expression of mucin subunits together with cytoskeletal fractions of collagens, myosin, F-actin, keratins, and tubulins. Taken as a whole, our results convincingly showed that the skin of M. electricus shares some structural similarities to other Siluriformes, however, it has some functional modifications that are implicated in protection, defense, and foraging behavior.

A new species of mailed catfish of genus Rhadinoloricaria (Siluriformes: Loricariidae: Loricariinae) from Rio Negro basin, Brazil.

During a recent collection expedition to the Rio Negro, in the state of Amazonas, Brazil, eight individuals of an unknown species were collected, with a combination of characteristics that placed the species in the genus Rhadinoloricaria. Furthermore, the presence of two autapomorphic characteristics, including numerous elongated papillae on the lower lip and unbranched barbelets on the margin of lower lip, suggests that it is a new species. From morphological and phylogenetic analyses, including the sequencing of specific genes to calculate the maximum likelihood analyses, coupled with osteological computed tomography (CT) scan analyses, the authors corroborated that the specimens represent a new species of Rhadinoloricaria, described in the present study.

Comparative reproductive biology of two sympatric Hypostomus in a Neotropical river.

Congeneric species often coexist in sympatry using behavioral and morphological adaptations to reduce competition and interspecific interference, but reproductive patterns behind coexistence remain unknown. We analyzed the gonadal morphology and development, reproductive cycle, and population structure of two sympatric congeneric fishes to evaluate the degree of overlap and differentiation of the reproductive biology between species in a Neotropical river. Development of testes and ovaries were similar between species, both showing asynchronous gonadal development, large diameter of gametes and synthesis of mucosubstances by follicle cells to form adhesive eggs. Although the morphometry of germ cells did not present differences, the zona radiata of mature eggs in Hypostomus garmani was markedly thicker than H. francisci, which suggests different spawning habitats. Both species have greater reproductive activity in the rainy season, concomitant with increase in water temperature, however H. garmani initiates and ends its reproduction earlier than H. francisci, indicating a differentiation of reproductive periods. Sexually mature males and females of H. francisci reproduced at a larger mean size then H. garmani. The two congeneric species had a similar abundance and sex ratios in the study area. Results show that although the species exhibited broad overlap of reproductive traits, a spatial and temporal differentiation of the reproductive biology was present. This study contributes to understanding reproductive mechanisms that may facilitate coexistence between congeneric sympatric species.

Topotype-Based Chromosomal Diversity among Five Species of Freshwater Armored Catfishes in the Hypostomus auroguttatus Supergroup (Actinopterygii: Siluriformes).

Freshwater catfishes from the genus Hypostomus have been models for several cytogenetic studies, due to their intense variability in diploid number, chromosome morphology, and the distribution of repetitive DNAs. Taking into consideration the taxonomic complexity inherent to this group, the present study aims to describe the karyotypes of five species of Hypostomus collected in their type localities: Hypostomus albopunctatus (Regan, 1908), Hypostomus hermanni (Ihering, 1905), Hypostomus iheringii (Regan, 1908), and Hypostomus paulinus (Ihering, 1905) from the Piracicaba River (the Upper Paraná River Basin); and Hypostomus mutucae Knaack, 1999 from the Claro River (the Upper Paraguay River Basin). Our results evidenced a great inter-specific diploid-number variation: 2n = 72 (H. hermanni); 2n = 74 (H. albopunctatus); 2n = 76 (H. paulinus); 2n = 80 (H. iheringii); and 2n = 82 (H. mutucae), which reflects the important role of Robertsonian rearrangements in the karyotypic differentiation among these species. The distribution of heterochromatin also varied considerably among species, making it possible to distinguish each analyzed species, as well as to detect microstructural variations among populations of the same species. These data can support taxonomic revisions when further associated with molecular markers and morphological analyses to delimit, more consistently, the taxonomic status of these Hypostomus species, which have a complex taxonomic diagnosis history.

Exceptional preservation of organs in Devonian placoderms from the Gogo lagerstätte.

The origin and early diversification of jawed vertebrates involved major changes to skeletal and soft anatomy. Skeletal transformations can be examined directly by studying fossil stem gnathostomes; however, preservation of soft anatomy is rare. We describe the only known example of a three-dimensionally mineralized heart, thick-walled stomach, and bilobed liver from arthrodire placoderms, stem gnathostomes from the Late Devonian Gogo Formation in Western Australia. The application of synchrotron and neutron microtomography to this material shows evidence of a flat S-shaped heart, which is well separated from the liver and other abdominal organs, and the absence of lungs. Arthrodires thus show the earliest phylogenetic evidence for repositioning of the gnathostome heart associated with the evolution of the complex neck region in jawed vertebrates.

Functional morphology of cardiac stomach of Nile catfish (Clarias gariepinus): Histological, scanning, and ultrastructural studies.

The present study was done on 20 adult specimens of Nile catfish (Clarias gariepinus) to demonstrate the morphological characteristics of the cardiac region of the stomach. The cardiac mucosa was characterized by a large number of well-defined long folds. The surface epithelial cells were simple columnar type covered with distinct microvilli and connected by desmosomes. Few PAS- and AB- positive goblet cells were found between the surface epithelium. In addition, many lymphocytes, macrophages, and blood capillaries were seen in the epithelial layer. The lamina propria was exclusively occupied by simple branched gastric (cardiac) glands that fill most of the thickness of the mucosa and open into gastric pits. The gastric glands were composed of numerous secretory tubules that were lined with one type of cells with a cytoplasm containing numerous electron-dense granules, well-developed rER, mitochondria, and a large number of free ribosomes. Moreover, macrophages were distributed in the lamina propria and submucosa. Telocytes were observed in the cardiac region for the first time around the glands, blood vessels, between the muscular layer, and in the serosa. A large number of mast cells could be identified in the submucosa around the blood vessels. The presence of many immune cells in the wall of the cardiac stomach suggests involvement in immune response in addition to its digestive function. RESEARCH HIGHLIGHTS: The study exposed many cell types in the wall of the cardiac stomach of Nile catfish including mast cells, lymphocytes, and neutrophils that suggests an involvement in the immune response. The current study is the first one to highlight the distribution of telocytes in the fish stomach.

Modulus adaptive lubricating prototype inspired by instant muscle hardening mechanism of catfish skin.

In nature, living organisms evolve unique functional components with mechanically adaptive compatibility to cater dynamic change of interface friction/lubrication. This mechanism can be used for developing intelligent artificial lubrication-regulation systems. Inspired by the muscle hardening-triggered lubrication of longsnout catfish, here we report a modulus adaptive lubricating hydrogel prototype consisting of top mucus-like hydrophilic lubricating layer and muscle-like bottom hydrogel that can stiffen via thermal-triggered phase separation. It exhibits instant switch from soft/high frictional state (~0.3 MPa, µ~0.37) to stiff/lubricating state (~120 MPa, µ~0.027) in water upon heating up. Such switchable lubrication is effective for wide range of normal loads and attributed to the modulus-dominated adaptive contact mechanism. As a proof-of-concept, switchable lubricating hydrogel bullets and patches are engineered for realizing controllable interface movements. These important results demonstrate potential applications in the fields of intelligent motion devices and soft robots.

The identity and distribution of striped bagrid catfish, Mystus tengara (Hamilton 1822) revealed through integrative taxonomy.

BACKGROUND: The taxonomic status and geographical distribution of M. tengara are vague. No genetic diversity and phylogenetic study have been done till now to resolve its identity and distribution. In the present study, an integrated taxonomic approach has been applied to clarify the taxonomic status, identity, and distribution of bagrid catfish, Mystus tengara. METHODS AND RESULTS: Comparative morphometric evaluation of M. tengara identified in the present study from distant geographical locations revealed variations of the traits in response to body length and environment, without significant genetic distance. The observed morphometric traits of M. tengara were found to be overlapping with available morphometric traits of M. tengara, M. carcio and M. vittatus. Maximum likelihood and Bayesian phylogenetic analysis based on mitochondrial cytochrome c oxidase (COI) gene also could not resolve their identity, and five paraphyletic clades comprising of M. tengara, M. vittatus, and M. carcio from India, Nepal, and Bangladesh were observed. Morphological and genetic evidence along with comparative evaluation of M. tengara, from its type locality, we consider M. tengara identified in the present study to be true, with its distribution extending from North East India to West Bengal, North India, Central India, Northern peninsular India, and Bangladesh. CONCLUSION: The observation of paraphyletic subclades and evaluation of genetic distance between subclades reveals the presence of four cryptic species. Further confirmation on the identity of M. vittatus and M. carcio, by an integrated taxonomic approach based on fresh specimens collected from the type locality, is required.

The Glyptothorax catfishes of the Euphrates and Tigris with the description of a new species (Teleostei: Sisoridae).

The Glyptothorax species inhabiting the Euphrates and Tigris drainages are reviewed and six species are recognised, one of which is described herein as new species. Glyptothorax armeniacus is endemic to headwater streams in the Euphrates drainage. Glyptothorax kurdistanicus is endemic to the upper Tigris downstream to the Lesser Zab drainage. Glyptothorax cous and G. steindachneri are riverine species widespread in both the Euphrates and Tigris drainages. Glyptothorax silviae is endemic to Iran. Glyptothorax daemon, new species, from the Greater Zab and Yanarsu in the upper Tigris drainage, is distinguished by having the thoracic adhesive apparatus strongly elevated, 1.11.2 times longer than wide, without tubercles on the head, well developed anteromedial striae, the medial pit without striae, and a short adipose fin. Glyptothorax daemon is separated into two mitochondrial lineages, externally indistinguishable and separated by a minimum K2P distance of 2.0% in the DNA barcode region. These lineages are paraphyletic in our analysis indicating past introgressive hybridisation with G. cous. All six species are diagnosed and all, except unstudied G. steindachneri, form distinct mitochondrial clades with between 1.2% and 3.4% minimum K2P distance between them. Species from the Euphrates and Tigris form a monophyletic mitochondrial group separated from 53 other Glyptothorax species studied from India and areas further east.

Variación fenotípica de los peces Curimata mivartii (Characiformes: Curimatidae) y Pimelodus grosskopfii (Siluriformes: Pimelodidae) en hábitats lóticos y lénticos / Phenotypic variation of the fishes Curimata mivartii (Characiformes: Curimatidae) and Pimelodus grosskopfii (Siluriformes: Pimelodidae) in lotic and lentic habitats

Resumen Introducción: A pesar de su importancia en el rendimiento de la natación y la eficacia biológica individual, la forma del cuerpo y las variaciones de tamaño en respuesta a la velocidad del flujo de agua siguen siendo desconocidas para la mayoría de los peces migratorios de agua dulce en el Neotrópico. Objetivo: Contrastar la hipótesis de variación fenotípica en el tamaño y la conformación del cuerpo de dos especies de peces dulceacuícolas que enfrentan cambios de velocidad a través de sus migraciones en dos ríos pertenecientes a una cuenca neotropical. Métodos: Se utilizó la morfometría geométrica basada en hitos para estudiar las variaciones en el tamaño y la conformación del cuerpo para dos especies de peces Curimata mivartii y Pimelodus grosskopfii en hábitats lóticos y lénticos de la cuenca Colombiana del Magdalena-Cauca. Resultados: Los individuos de C. mivartii de dos hábitats lóticos fueron similares en tamaño y significativamente más grandes que los del hábitat léntico, mientras que los individuos de P. grosskopfii fueron similares en ambos hábitats. Ambas especies mostraron cuerpos más hidrodinámicos en hábitats lóticos y formas corporales más robustas en hábitats lénticos. Conclusión: Ambas especies exhiben cambios fenotípicos en la forma del cuerpo concordantes con las predicciones previas sobre las variaciones morfológicas de los peces. Esta información es relevante para predecir cambios en respuesta a la heterogeneidad ambiental, especialmente inducidos por actividades antropogénicas que cambian las velocidades del agua en el río.

Abstract Introduction: Despite their importance in swimming performance and individual fitness, body shape and size variations in response to water flow velocity remain unknown for most migratory freshwater fishes in the Neotropics. Objective: Test the hypothesis of phenotypic variation in the size and body shape of two species of freshwater fishes that encounter changes in water velocity across their migrations in two rivers that belong to a single Neotropical basin. Methods: Landmark-based geometric morphometrics was used to study variations in body size and shape for the fish species Curimata mivartii and Pimelodus grosskopfii in lotic and lentic habitats of the Colombian Magdalena-Cauca Basin. Results: Individuals of C. mivartii from two lotic habitats were similar in size and both were significantly bigger than those from lentic habitats, whereas individuals of P. grosskopfii were similar in size in both habitats. Both species showed more streamlined bodies in lotic habitats and deeper body shapes in lentic habitats. Conclusions: Both species exhibit phenotypic changes in body shape concordant with previous predictions on morphological variations of fishes. This information is relevant to predict changes in response to environmental heterogeneity, especially those induced by anthropogenic activities that change the water velocity in the river.

Ontogeny and development of the gastrointestinal system in Indian walking catfish (Clarias magur) during its early development.

Ontogeny of the digestive tract and its accessory organs and their further development in the Indian walking catfish (Clarias magur) were examined in larvae, starting from the day of hatching until 35 days post-hatching (dph) reared at 28-29 °C. Many organs at their primordial stage were seen on the day of hatching. These include opened oral cavity with monolayered epithelial lining and very few newly emerging taste buds and goblet cells, primordial pharyngeal teeth on slightly stratified epithelia of the pharyngeal plate, stomach anlage with some degree of the mucosal fold, and a few newly forming gastric glands embedded under its mucosa, primordial anterior and posterior intestine with the smooth mucosal surface, anal opening, and primordial liver and pancreas. At 1 dph, the stomach appeared to be bilobed with the first evidence of food particle in it, and the intestine had some initial folding. On the day of hatching, goblet cells appeared in all lengths of the gut, but not densely, except in the stomach; on it, they appeared at 2 dph. Pancreatic zymogen granules also appeared on this day. Supranuclear vesicles first appeared on 4-5 dph (7.9 ± 0.5-8.6 ± 0.8 mm TL), and they continue to exist until 35 dph. The developmental sequence in this fish confirmed it as an altricial species with some major histomorphological events after the onset of feeding; these include-the appearance of fully developed-pharyngeal teeth at 4 dph and onwards, pyloric sphincter, anterior to posterior intestinal sphincter at 6 dph, and the continuous development of buccopharyngeal cavity and stomach in their shape, size, and functionality until the completion of metamorphosis. Overall, the information on gastrointestinal development in the early life stage of C. magur will be useful for understanding its larval digestive physiology, and this, in turn, will help in designing effective larval feed for growth and survival.

A combined molecular and morphological phylogeny of the Loricariinae (Siluriformes: Loricariidae), with emphasis on the Harttiini and Farlowellini.

We present a combined molecular and morphological phylogenetic analysis of the Loricariinae, with emphasis on the Harttiini (Cteniloricaria, Harttia, and Harttiella) and Farlowellini (Aposturisoma, Farlowella, Lamontichthys, Pterosturisoma, Sturisoma, and Sturisomatichthys). Character sampling comprised seven molecular markers (the mitochondrial Cytb, nd2, 12S and 16S, and the nuclear MyH6, RAG1 and RAG2) and 196 morphological characters. A total of 1,059 specimens, and 159 tissue samples were analized, representing 100 species. A Bayesian Inference analysis was performed using the concatenated data matrix, which is comprised of 6,819 characters. The Loricariinae were found to comprise the tribes (Hartiini (Loricariini, Farlowellini)), the latter two elevated from subtribes. A Maximum Parsimony analysis was also performed using the same data matrix in order to reveal phenotypical synapomorphies to diagnose each clade. Two MP trees were found with a length of 14,704 steps, consistency index of 0.29 and retention index of 0.61, which were summarized in a strict consensus tree. Harttiini includes (Harttiella (Cteniloricaria, Harttia), and Farlowellini includes (Lamontichthys (Pterosturisoma (Sturisoma (Sturisomatichthys, Farlowella)))). Aposturisoma was recovered nested within Farlowella and is synonymyzed to the latter. Sturisoma was corroborated as strictly cis-Andean, while Sturisomatichthys encompasses, besides the valid species already included in the genus, the trans-Andean species once belonging to Sturisoma sensu lato. Identification keys and phylogenetic diagnoses of family-group taxa and genera of both the Harttiini and the Farlowellini are provided.

Morphometric and population genomic evidence for species divergence in the Chimarrichthys fish complex of the Tibetan Plateau.

The uplift of the Tibetan Plateau altered the environmental conditions of the local area substantially. Here, we conducted a comprehensive investigation based on morphometrics, population genomics, and climatic factors to evaluate phenotypic and genome-level variations in a radiation of Chimarrichthys catfish endemic to the Plateau. Discriminant function analysis showed phenotypic differences of Chimarrichthys between rivers with respect to elevation. Genetic structure analysis based on 6606 single nucleotide polymorphisms (SNPs) deduced genetic differences between rivers, and species delimitation indicated that the Chimarrichthys fish complex could be divided into three species. Restriction site-associated DNA tags were mapped to the gene sets of Glyptosternon maculatum, and matches were searched against databases for Gene Ontology annotation. Genomic regions exhibiting marked differences among localities represented a range of biological functions, including growth (gdf11), bone development (bmp8a), cellular response to light stimulus (opn3), regulation of the rhodopsin-mediated signalling pathway (grk1), immune response (rag1 and ung), reproductive process (antxr2), and regulation of intracellular iron levels (ireb2). The tag44126, where gene gdf11 is located, was identified as an outlier exhibiting divergence between rivers with altitude differences, and the SNP is thymine (T) in Dadu and Yalong River (~2700 m), but guanine (G) in Jinsha and Qingyi rivers (~2200 and ~ 684 m), suggesting a possible effect of altitude on its differentiation.

Taxonomic revision of Hopliancistrus Isbrücker & Nijssen, 1989 (Siluriformes, Loricariidae) with redescription of Hopliancistrus tricornis and description of four new species.

Hopliancistrus is an Ancistrini genus diagnosed by having few and very strong cheek odontodes on interopercular area, and a patch of strong and stiff odontodes on the antero-lateral border of the snout. The type species is herein redescribed based on types and recently collected specimens. In addition, four new congeneric species are described based on specimens collected in other parts of the Rio Xingu and Rio Tapajós basins. Hopliancistrus tricornis is distributed in the lower Rio Tapajós and is diagnosed by the possession of four branched anal-fin rays and relatively large white to yellow spots on trunk and pectoral and pelvic fins, and dark brown spots on dorsal, caudal and anal fins. Hopliancistrus munduruku is described based on specimens from Rio Jamanxim (Rio Tapajós basin) and Rio Curuá (Rio Xingu basin) and is diagnosed by the possession of five branched anal-fin rays and large yellow blotches on trunk and dark brown to black spots over the fins. Hopliancistrus wolverine is distributed in the rapids of the lower and middle Rio Xingu and is diagnosed by the possession of five branched anal-fin rays and conspicuous small yellow dots on head, trunk and fins. Hopliancistrus xikrin is distributed in medium- to small-sized tributaries of the lower portion of Rio Xingu basin, and is diagnosed by absence of contact between the transverse process of the first dorsal-fin pterygiophore and the transverse process of the second pterygiophore. Hopliancistrus xavante is distributed in the tributaries of upper Rio Xingu basin, and is diagnosed by having a thick skin covering the nuchal plate; by having large white spots on trunk and fins; and by the possession of five branched anal-fin rays. An osteological description and a key for species identification are also provided.

When destruction comes first: Two new species of Hypostomus Lacépède, 1803 (Siluriformes: Loricariidae) from a deeply-impacted river in the Rio São Francisco basin in Brazil.

Environmental disasters affecting Brazilian rivers have been frequent recently, especially involving mining activities. Two recent dam-rupture events suddenly released millions of cubic meters of iron tailings downstream into two major Brazilian watersheds. These events generated major losses to the environment and human life. Additionally, the biodiversity in both watersheds was still incompletely known. Two new species of the armoured catfish genus Hypostomus were discovered in the Rio Paraopeba and surrounding rivers of the Rio São Francisco Basin. The species share some main characteristics including a depressed body, large dark spots on a clearer background and the absence of keels on flanks. However, while one species (Hypostomus freirei sp. n.) has a large mandibular ramus and numerous slender teeth, the other (Hypostomus guajupia sp. n.) has a shorter mandibular ramus and few robust teeth. The discovery of these two new mid-sized fish species emphasizes the presumption that the effects of major environmental disasters cannot be fully estimated as local biodiversity is not completely known. This discovery in a recently devastated area also shows that tough environmental laws for the protection, supervision and mitigation of major impacts are urgently needed in developing countries.

Ontogeny of the brain of Microglanis garavelloi Shibatta and Benine 2005 (Teleostei: Siluriformes: Pseudopimelodidae).

The gross brain morphology and the peripheral olfactory organ of Microglanis garavelloi are described throughout development, and the relationship of these organs to the general behaviour of the species is discussed. During the development, the main brain subdivisions undergo a series of morphological changes keeping a relatively constant volume increase. However, we observed different growth rates in the brains of males and females when these were compared. During the maturation process, a series of hormonal events result in the development of some secondary sexual traits in the brain of male specimens, like faster growth rate of brain areas linked to motor control, olfactory and visual responses. The number of olfactory-organ lamellae increases continuously in both males and females, during their maturation period. These results suggest that changes may be caused by cognitive demands that this species is exposed to throughout its lifespan. The gross morphological arrangement of the central nervous system indicates shared patterns with other members of the family Pseudopimelodidae.

Molecular and morphological diversity in species of Kronichthys (Teleostei, Loricariidae) from Atlantic coastal rivers of Brazil.

The Neotropical catfish genus Kronichthys contains three species distributed along coastal rivers of southern and southeastern Brazil. Although phylogenetic hypotheses are available, the molecular and morphological diversity and species boundaries within the genus remain unexplored. In this study, the authors generated mitochondrial data for 90 specimens combined with morphometric and meristic data to investigate species diversity, species boundaries and putative morphological signatures in Kronichthys. Phylogenetic and species delimitation results clearly show the presence of four genetic lineages, three within Kronichthys heylandi along the coast from Rio de Janeiro to southern São Paulo and a single lineage encompassing both the nominal species Kronichthys lacerta and Kronichthys subteres from the Ribeira de Iguape basin to Santa Catarina in southern Brazil. Nonetheless, morphological data show overlapped ranges in morphometrics and a definition of only two morphotypes, with clear phenotypic differences in the teeth number: K. heylandi differs from K. subteres + K. lacerta by the higher number of premaxillary teeth (30-52 vs. 19-28) and higher number of dentary teeth (28-54 vs. 17-28). Headwater captures and connections of paleodrainages because of sea-level fluctuations represent the two major biogeographic processes promoting species diversification and lineage dispersal of Kronichthys in the Atlantic coastal range of Brazil.

Morphological diversity of acoustic and electric communication systems of mochokid catfish.

Mochokid catfish offer a distinct opportunity to study a communication system transitioning to a new signaling channel because some produce sounds and others electric discharges. Both signals are generated using an elastic spring system (ESS), which includes a protractor muscle innervated by motoneurons within the protractor nucleus that also has a motoneuron afferent population. Synodontis grandiops and S. nigriventris produce sounds and electric discharges, respectively, and their ESSs show several morphological and physiological differences. The extent to which these differences explain different signal types remains unclear. Here, we compare ESS morphologies and behavioral phenotypes among five mochokids. S. grandiops and S. nigriventris were compared with Synodontis eupterus that is known to produce both signal types, and representative members of two sister genera, Microsynodontis cf. batesii and Mochokiella paynei, for which no data were available. We provide support for the hypothesis that peripheral and central components of the ESS are conserved among mochokids. We also show that the two nonsynodontids are only sonic, consistent with sound production being an ancestral character for mochokids. Even though the three sound producing-only species differ in some ESS characters, several are similar and likely associated with only sound production. We propose that the ability of S. eupterus to generate both electric discharges and sounds may depend on a protractor muscle intermediate in morphology between sound producing-only and electric discharge-only species, and two separate populations of protractor motoneurons. Our results further suggest that an electrogenic ESS in synodontids is an exaptation of a sound producing ESS.

Genetic and morphological assessment of a vulnerable large catfish, Silonia silondia (Hamilton, 1822), in natural populations from India.

Silonia silondia is a commercially important fish distributed in Asian countries, which is under threat due to overexploitation. This study focuses on the morphological analysis and genetic variation of S. silondia individuals, through truss network and sequencing of two mitochondrial regions, respectively, from six wild populations of the Ganga and Mahanadi river systems in India. A total of 38 haplotypes was observed by analysing combined mitochondrial genes (cytochrome b + ATPase 6/8) in 247 individuals of S. silondia collected from six populations. Average haplotype and nucleotide diversities were 0.8508 and 0.00231, respectively. Genetic structure analysis showed the predominant cause of genetic variation to be within populations. The two clades were observed among the haplotypes and time of divergence from their most probable ancestor was estimated to be around 0.3949 mya. Analysis of combined mitochondrial genes in six populations of S. silondia resulted into three management units or genetic stocks. The truss network analysis was carried out by interconnecting 12 landmarks from digital images of specimens to identify phenotypic stocks. Sixty-five truss morphometric variables were analysed for geometric shape variation which revealed morphological divergence in River Son specimens. The present study presents molecular markers and genetic diversity data which can be critical input for conservation and management of differentiated populations and future monitoring of the genetic bottleneck. The morphological shape analysis clearly shows that variation in the insertion of adipose fin is an important parameter influencing the morphological discrimination.

Loricaria cuffyi (Siluriformes: Loricariidae), a new species of loricariin catfish from the Guiana Shield.

Loricaria cuffyi n. sp. is described based on 36 specimens from the Essequibo and upper Negro River drainages in western Guyana and the upper Orinoco River drainage in Venezuela. The new species can be distinguished from sympatric and geographically proximate congeners by a postorbital notch that is inconspicuous, shallow and rounded, odontode ridges on the dorsum of head and predorsal weakly developed, abdominal plates tightly joined and completely covering the median abdominal space and pectoral girdle, higher anterior lateral plate counts, and coloration characteristics. The distribution of the new species adds to an interesting and well-documented biogeographical pattern exhibited by other Guiana Shield loricariids influenced by the proto-Berbice during the Cenozoic and recent configuration of drainages in the Guiana Shield. We present an update on the taxonomy of Loricaria, and discuss the biogeography and conservation status of the new species.