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Cave-adapted animals evolve a suite of regressive and constructive traits that allow survival in the dark. Most studies aiming at understanding cave animal evolution have focused on the genetics and environmental underpinnings of regressive traits, with special emphasis on vision loss. Possibly as a result of vision loss, other non-visual sensory systems have expanded and compensated in cave species. For instance, in many cave-dwelling fish species, including the blind cavefish of the Mexican tetra, Astyanax mexicanus, a major non-visual mechanosensory system called the lateral line, compensated for vision loss through morphological expansions. While substantial work has shed light on constructive adaptation of this system, there are still many open questions regarding its developmental origin, synaptic plasticity, and overall adaptive value. This review provides a snapshot of the current state of knowledge of lateral line adaption in A. mexicanus, with an emphasis on anatomy, synaptic plasticity, and behavior. Multiple open avenues for future research in this system, and how these can be leveraged as tools for both evolutionary biology and evolutionary medicine, are discussed.

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Intercellular protuberances (IPs) are projections on the cell surface and have been reported for families of ferns, Gymnosperms, and Angiosperms. Data on the type, chemical composition, and distribution of these structures among vascular plants are still scarce. Here, we investigate the occurrence, distribution, type of IPs among species of eight Dennstaedtiaceae genera and verify the taxonomic significance of these protuberances in the family. Rhizomes of 23 species of Dennstaedtiaceae from field and herbaria collections were analyzed by light microscopy and scanning electron microscopy. Histochemical tests were performed to identify the main classes of IPs chemical compounds. Two types of IPs were observed in Dennstaedtiaceae species: strand and filament types. They were observed in the intercellular spaces of the parenchyma in the cortex and pith regions. Overall, protuberances are irregularly shaped, with angustate or spheroidal apices. Their polysaccharide nature and pectic constitution were confirmed by histochemical tests. Concerning Pteridium arachnoideum (Kaulf.) Maxon subsp. arachnoideum, IPs have confirmed phenolic composition. Evidence indicates that IPs in Dennstaedtiaceae originate from the fragmentation of the middle lamella and that they have a structural function as well as protection against pathogens. In lateral-line aerenchyma, the occurrence of filament-type IPs may be related to the larger intercellular spacing in the cortex region, providing greater mechanical resistance. We have expanded the data on the occurrence of IPs in the Dennstaedtiaceae, which appear to be notable characters for the family. Moreover, the data presented herein confirmed the polysaccharide and pectic nature of these structures. However, we were unable to find links between IPs and taxonomy and evolution of the Dennstaedtiaceae. On the other hand, different IPs types were identified between the clades Dennstaedtioideae (strand-type IPs) and Hypolepidoideae (filament-type IPs, with exceptions).(AU)

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As most neotropical pipids, the four species of Pipa present in Colombia are poorly understood despite their particular biology. The tegument of these New-World pipids presents particular structures which variations have been hardly analyzed. Therefore, we aim to describe the morphological variations of the dermal flap, barbels, fingertips, and the lateral line pattern among these four species, focusing on changes during the ontogeny. The results of the study show that the dermal flap was exclusively found in P. pipa, while barbels are usually present in P. pipa but seldom in P. snethlageae. The lateral line pattern in the dorsum is shared by the four species, but P. pipa present more neuromast lines along the snout than P. snethlageae. These species were different from P. parva and P. myersi, which cannot be distinguished based on external morphology, as they were more similar in all lateral line elements and exhibited the same fingertip morphology. On the other hand, the fingertips of young individuals of P. pipa and P. snethlageae presented four simple distal lobes which bifurcate twice during the ontogeny, so that adults present sixteen lobes. The difference between species is observed in the fingertip morphology: P. pipa has all four lobes distally placed, but P. snethlageae has one pair more proximal. The tegument structures analyzed here have a taxonomic utility using external morphology for P. pipa and P. snethlageae, but for P. parva and P. myersi additional studies are necessary. For future research, evaluating the function and anatomy of these structures is important to the understanding these integumentary structures in Pipa.(AU)

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A new species of Astyanax is described from the rio Salobra, tributary of rio Cuiabá, rio Paraguai basin. The new taxon can be distinguished from its congeners by having a well-defined dark midlateral stripe on body extending from the posterior margin of the opercle to the base of middle caudal-fin rays and a single vertical elongate humeral blotch. Although the new species is described in Astyanax, some specimens present an incomplete or a discontinuous series of perforated scales in the lateral line. Therefore, a discussion on its generic allocation is presented. Comments on different patterns of coloration among dark-striped species of Astyanax are also provided. The discovery of a new species in an underwater tourist point relatively near a large urban center underscores that even fish species daily observed by hundreds of people in limpid waters may lack a formal taxonomic identity. Such finding also highlights how the megadiverse Brazilian freshwater ichthyofauna still needs efforts and investments to identify and describe new taxa.(AU)

Uma nova espécie de Astyanax é descrita do rio Salobra, afluente do rio Cuiabá, bacia do rio Paraguai. O táxon novo pode ser diferenciado de seus congêneres por apresentar uma faixa médio-lateral escura bem definida no corpo, se estendendo da margem posterior do opérculo até a base dos raios medianos da nadadeira caudal e por possuir uma mancha umeral verticalmente alongada. Apesar da espécie nova ser descrita em Astyanax, alguns exemplares apresentam uma série incompleta ou descontínua de escamas perfuradas na linha lateral. Assim, uma discussão sobre sua alocação genérica é apresentada. Comentários sobre os diferentes padrões de coloração de espécies de Astyanax com faixa escura também são fornecidos. A descoberta de uma espécie nova em um ponto turístico subaquático relativamente próximo a um grande centro urbano ressalta que mesmo as espécies de peixes observadas diariamente por centenas de pessoas em águas límpidas podem não ter uma identidade taxonômica formal. Tal achado também evidencia o quanto a megadiversa ictiofauna de água doce brasileira ainda precisa de esforços de coleta adicionais e investimentos para identificar e descrever os táxons novos.(AU)

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Vertebrate hair cell (HC) systems are innervated by efferent fibers that modulate their response to external stimuli. In mammals, the best studied efferent-HC synapse, the cholinergic medial olivocochlear (MOC) efferent system, makes direct synaptic contacts with HCs. The net effect of MOC activity is to hyperpolarize HCs through the activation of α9α10 nicotinic cholinergic receptors (nAChRs) and the subsequent activation of Ca2+-dependent SK2 potassium channels. A serious obstacle in research on many mammalian sensory systems in their native context is that their constituent neurons are difficult to access even in newborn animals, hampering circuit observation, mapping, or controlled manipulation. By contrast, fishes and amphibians have a superficial and accessible mechanosensory system, the lateral line (LL), which circumvents many of these problems. LL responsiveness is modulated by efferent neurons which aid to distinguish between external and self-generated stimuli. One component of the LL efferent system is cholinergic and its activation inhibits LL afferent activity, similar to what has been described for MOC efferents. The zebrafish (Danio rerio) has emerged as a powerful model system for studying human hearing and balance disorders, since LL HC are structurally and functionally analogous to cochlear HCs, but are optically and pharmacologically accessible within an intact specimen. Complementing mammalian studies, zebrafish have been used to gain significant insights into many facets of HC biology, including mechanotransduction and synaptic physiology as well as mechanisms of both hereditary and acquired HC dysfunction. With the rise of the zebrafish LL as a model in which to study auditory system function and disease, there has been an increased interest in studying its efferent system and evaluate the similarity between mammalian and piscine efferent synapses. Advances derived from studies in zebrafish include understanding the effect of the LL efferent system on HC and afferent activity, and revealing that an α9-containing nAChR, functionally coupled to SK channels, operates at the LL efferent synapse. In this review, we discuss the tools and findings of these recent investigations into zebrafish efferent-HC synapse, their commonalities with the mammalian counterpart and discuss several emerging areas for future studies.

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Collective cell migration drives the formation of complex organ systems as well as certain tumour invasions and wound healing processes. A characteristic feature of many migrating collectives is tissue-scale polarity, whereby 'leader' cells at the tissue edge guide 'followers' cells that become assembled into polarized epithelial tissues. In this study, we employed particle image velocimetry (PIV) as a tool to quantitate local dynamics underlying the migration of the posterior lateral line primordium (pLLP) in zebrafish at a short time scale. Epithelial cadherin-EGFP was the fluorescent tracer in time-lapse images for PIV analysis. At the tissue level, global speed and directionality of the primordium were extracted from spatially averaged velocity fields. Interestingly, fluctuating velocity patterns evolve at the mesoscale level, which distinguishes the pseudo-mesenchymal leading front from the epithelialized trailing edge, and superimpose to the global deceleration of the whole primordium during the separation of a protoneuromast. Local velocity fields obtained by PIV proved sensitive to estimate the migration speed and directionality of the pLLP in zebrafish, predicting protoneuromast separation at short time scales. Finally, the PIV approach may be suitable for analysing the dynamics of otherin vivomodels of collective migration.

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A new species of Eigenmannia is described from the Rio Paraná (the Grande, Paranapanema and Tietê basins). This new species is distinguished from all congeners by colouration pattern, position of the mouth, relative depth of posterodorsal expansion on infraorbitals 1 + 2, number of teeth, osteological features, number of rows of scales above lateral line (LL) and morphometric data. Comments on the widened cephalic lateral-line canals of Sternopygidae and a dichotomous key to the species of Eigenmannia from the Rio Paraná Basin are provided.

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The lateral line (LL) is a sensory system that allows fish and amphibians to detect water currents. LL responsiveness is modulated by efferent neurons that aid in distinguishing between external and self-generated stimuli, maintaining sensitivity to relevant cues. One component of the efferent system is cholinergic, the activation of which inhibits afferent activity. LL hair cells (HCs) share structural, functional, and molecular similarities with those of the cochlea, making them a popular model for studying human hearing and balance disorders. Because of these commonalities, one could propose that the receptor at the LL efferent synapse is a α9α10 nicotinic acetylcholine receptor (nAChR). However, the identities of the molecular players underlying ACh-mediated inhibition in the LL remain unknown. Surprisingly, through the analysis of single-cell expression studies and in situ hybridization, we describe that α9, but not the α10, subunits are enriched in zebrafish HCs. Moreover, the heterologous expression of zebrafish α9 subunits indicates that homomeric receptors are functional and exhibit robust ACh-gated currents blocked by α-bungarotoxin and strychnine. In addition, in vivo Ca2+ imaging on mechanically stimulated zebrafish LL HCs show that ACh elicits a decrease in evoked Ca2+ signals, regardless of HC polarity. This effect is blocked by both α-bungarotoxin and apamin, indicating coupling of ACh-mediated effects to small-conductance Ca2+-activated potassium (SKs) channels. Our results indicate that an α9-containing (α9*) nAChR operates at the zebrafish LL efferent synapse. Moreover, the activation of α9* nAChRs most likely leads to LL HC hyperpolarization served by SK channels.SIGNIFICANCE STATEMENT The fish lateral line (LL) mechanosensory system shares structural, functional, and molecular similarities with those of the mammalian cochlea. Thus, it has become an accessible model for studying human hearing and balance disorders. However, the molecular players serving efferent control of LL hair cell (HC) activity have not been identified. Here we demonstrate that, different from the hearing organ of vertebrate species, a nicotinic acetylcholine receptor composed only of α9 subunits operates at the LL efferent synapse. Activation of α9-containing receptors leads to LL HC hyperpolarization because of the opening of small-conductance Ca2+-activated potassium channels. These results will further aid in the interpretation of data obtained from LL HCs as a model for cochlear HCs.

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Moenkhausia cotinho is redescribed based on the examination of meristic and morphometric data and external morphological characters of specimens from the Amazon and Orinoco basins and from rivers in the Guyana. The species is distinguished from congeners based on the combination of a reticulate color pattern, the presence of dark spots on the posterior edge of scales of the longitudinal rows dorsal to the lateral line, the presence of a dark blotch on the caudal-fin base failing to reach the posterior tip of the middle caudal-fin rays; the dorsal region of the eyes red to orange in life; 5/3 longitudinal series of scales, above and below the lateral line, respectively; and the tips of the pectoral-fin rays not extending beyond the base of the pelvic fin. All specimens of M. cotinho have a completely pored literal line except for a few specimens from drainages in the Guyana. The redefinition of the taxonomic limits and geographic distribution of M. cotinho allowed us to reevaluate the taxonomic limits and geographic distribution of Hemigrammus newboldi, the identity of which has been previously questioned, but which is clearly diagnosed from M. cotinho based on the relatively longer pectoral fin, the presence of conical teeth in the posterior portion of the dentary, the absence of a reticulate color pattern of body and in the shorter longitudinal dark stripe on body. In addition, two new species of Moenkhausia are described: Moenkhausia rondoni sp n. from the rio Madeira basin, Brazil and Moenkhausia pirahan sp n. from the lower rio Madeira and rio Trombetas and rio Tapajós basins, Brazil.

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Arapaima gigas, one of the world's largest freshwater fish, is considered an emerging species for aquaculture development in Brazil given its high growth rate and meat quality. However, the lack of reproductive control in captivity has limited the expansion of Arapaima farming. This study aimed to test the effects of hormonal induction using mGnRHa implants and size pairing on broodstock reproduction through the analyses of sex steroids. To do so, broodstock of different sizes (large, small or mixed) were paired and implanted. Plasma and cephalic secretion profiles of testosterone (T), 11-ketotestosterone (11-KT) and 17ß-oestradiol (E2) were analysed. Compared to control (non-implanted), implanted broodstock showed a significant increase in plasma 11-KT (large and small males) and T (large and mixed females) post GnRHa implantation. In females, a significant increase in plasma T levels was shown, however, E2 remained unchanged after implantation. Despite the lack of clear spawning induction, this study showed the potency of GnRHa on sex steroid production regardless of pairing groups. Interestingly, significant correlations between blood plasma and cephalic secretion levels of 11-KT in males and T in females were observed, indicating the possible release of pheromones through the cephalic canals of A. gigas.

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The lateral line is the primary modality fish use to create a hydrodynamic image of their environment. These images contribute to a variety of behaviors, from rheotaxis to escape responses. Here we discern the contributions of visual and lateral line modalities in hunting behavior of larvae that have developed under different photic conditions. In particular, cave animals have a hypertrophied sense of mechanosensation, and we studied the common animal model cavefish Astyanax mexicanus and its closest related surface relative. We raised larvae in a diurnal light-dark regimen and in complete darkness. We then examined the distribution of neuromasts in their lateral lines, and their hunting performance in light and dark conditions, with and without the contribution of the lateral line. We report that all larva depend on the lateral line for success in hunting and that surface fish raised in the dark have a greater dependency on the lateral line.

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The lateral line system in anurans is functional during aquatic stages and therefore could provide characters related to larval morphological variation. However, few studies have addressed its components in an integrated overview, and little is known about its ontogenetic variation. This study describes the postembryonic trajectory of the lateral system in Telmatobius atacamensis up to its metamorphic regression. This includes structure, number, topography, and innervation of neuromasts, to contribute new and complete information about its larval organization and its temporal sequence of regression. The arrangement and innervation of lateral lines in T. atacamensis resembles those described for other Type IV tadpoles. Its distinctive features are the orientation of the neuromast stitches in the lateral lines, the presence of supraotic neuromasts, and the first-described case of asymmetry of the ventral trunk line. The temporal sequence of regression during metamorphosis differs between the lateral lines and the lateral line nerves, which remain myelinated into postmetamorphic stages. This asynchronous pattern between different components of the system has also been described for Pseudis paradoxa, which shares with T. atacamensis a remarkably long larval period. This long larval period and gradual metamorphosis could also be related to the constitutive metamorphic regression of the system, in spite of the aquatic lifestyle of these frogs.

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Astyanax lorien and A. rupestris are described from tributaries of upper rio Paraguaçu basin, Bahia, Brazil. Both species shares the majority of the characters currently used to define the Astyanax scabripinnis species complex, with highest body depth approximately at vertical through pectoral-fin midlength and a low number of branched anal-fin rays (15-21). Astyanax lorien is distinguished from its congeners by a combination of characters, including presence of small bony hooks on all fins of mature males, a unique vertically elongate humeral blotch, and ventral margin of the third infraorbital close to the horizontal limb of preopercle. Astyanax rupestris is distinguished from its congeners also by a combination of characters, including ventral margin of third infraorbital distinctly separated from horizontal limb of preopercle, leaving a broad area without superficial bones, absence of midlateral stripe on body, absence of blotch on caudal peduncle, and presence of a vertically elongated conspicuous dark humeral blotch, not bordered anteriorly and posteriorly by distinct unpigmented areas. Both species are apparently endemic to the upper portion of the Paraguaçu river basin, within the Chapada Diamantina domain.

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A new species of Pimelodella is described from several right-bank tributaries of the Rio Madeira basin in Amazonas and Rondônia states, Brazil. The new species differs from all congeners by the supraoccipital process not reaching the anterior nuchal plate, 43-45 total vertebrae, maxillary barbels reaching between adpressed anal-fin terminus and caudal-fin origin, epiphyseal branch of supraorbital laterosensory canal emerging as two distantly-positioned pores and a conspicuous black mark at distal third of dorsal fin, between dorsal-fin spine and third branched ray. A detailed description of the cephalic laterosensory system of the new species is provided and contrasted with other Siluriformes and Ostariophysi. A discussion regarding homology of the catfish upper pectoral girdle bones is offered in light of modifications of the postotic and supratemporal lateral-line canals. Based on the placement of the pterotic branch of the postotic canal, it is concluded that the extrascapula is fused to the pterotic in Siluriformes. Results presented herein offer an example of how lateral-line morphology can be used as a compelling source of evidence to help determine homology of cranial and upper pectoral girdle bones.

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Resumen Se presenta la descripción de la composición y arreglo estructural del sistema de la línea lateral de tres especies de rayas eléctricas (Narcine bancroftii, N. entemedor y N. vermiculatus). Las tres especies muestran los canales supraorbital (SO), infraorbital (IO), hiomandibular (HYO) y de la línea lateral posterior (LLP), menos ramificados que en otros batoideos. Narcine entemedor difiere de sus congéneres por la gran ramificación de los canales SO e IO, los cuales convergen en la región inter-orbital; en N. vermiculatus estos canales presentan una condición similar, pero con una menor ramificación. En contraste N. bancroftii presenta los canales divergentes (dirigidos hacia afuera de la región inter-orbital). Los canales HYO están localizados en la periferia de los órganos eléctricos en estas especies; en N. bancroftii las ramificaciones se extienden hacia la región posterior, mientras que en las demás especies están reducidas (N. entemedor) o casi ausentes (N. vermiculatus). La LLP es de forma curva y está dirigida hacia el urostilo, asimismo muestra un gran número de ramificaciones, excepto en N. vermiculatus. La información sobre el arreglo y el número de poros sobre el sistema de canales de la LL en Narcine, puede ser de utilidad para la distinción taxonómica de sus especies, tal como ha sido corroborado para otros Torpediniformes.

Abstract This study describes the composition and structural arrangement of the lateral line system of three electric ray species (Narcine bancroftii, N. entemedor and N. vermiculatus). All three species showed the supraorbital (SO), infraorbital (IO), hyomandibular (HYO) and posterior lateral line (PLL) canals, less branched compared to other batoids. Narcine entemedor differs from its congeners by the extensive branching of the SO and IO canals, which converge in the inter-orbital region; in N. vermiculatus these canals present a similar condition, but are less branched. In contrast, N. bancroftii has divergent canals (directed outwards from the inter-orbital region). HYO canals are located on the periphery of the electric organs in these species; in N. bancroftii the branches extend towards the posterior region, whereas in the other species are reduced (N. entemedor) or almost absent (N. vermiculatus). The PLL is curved and projected towards the urostyle, it also shows a large number of ramifications, except in N. vermiculatus. Information about the LL canal system arrangement and pore number in Narcine can be useful for the taxonomic distinction of its species, as it has been corroborated in other Torpediniformes. Rev. Biol. Trop. 66(2): 586-592. Epub 2018 June 01.

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The laterosensory system is a mechanosensory modality involved in many aspects of fish biology and behavior. Laterosensory perception may be crucial for individual survival, especially in habitats where other sensory modalities are generally useless, such as the permanently aphotic subterranean environment. In the present study, we describe the laterosensory canal system of epigean and subterranean species of the genus Ituglanis (Siluriformes: Trichomycteridae). With seven independent colonizations of the subterranean environment in a limited geographical range coupled with a high diversity of epigean forms, the genus is an excellent model for the study of morphological specialization to hypogean life. The comparison between epigean and subterranean species reveals a trend toward reduction of the laterosensory canal system in the subterranean species, coupled with higher intraspecific variability and asymmetry. This trend is mirrored in other subterranean fishes and in species living in different confined spaces, like the interstitial environment. Therefore, we propose that the reduction of the laterosensory canal system should be regarded as a troglomorphic (= cave-related) character for subterranean fishes. We also comment about the patterns of the laterosensory canal system in trichomycterids and use the diversity of this system among species of Ituglanis to infer phylogenetic relationships within the genus. J. Morphol. 278:4-28, 2017. ©© 2016 Wiley Periodicals,Inc.

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A new species of Boehlkea is described from rio Japurá, Amazon basin. The new species differs from B. fredcochui by the presence of a vertically elongate humeral spot (vs. absence), complete lateral line (vs. incomplete), four rows of scales below lateral line (vs. three), and lower number of branched anal-fin rays (17-21 vs. 22-25), and from B. orcesi by the higher number of maxillary teeth (13-14 vs. 5-12), greater head length (27.9-29.9% vs. 24.3-27.5% of SL), and by the color pattern (basal half of dorsal-fin, distal portion of pelvic-fin, lower caudal-fin lobe and anal-fin with black chromatophores vs. absence of black chromatophores in the fins).(AU)

Uma nova espécie de Boehlkea é descrita do rio Japurá, bacia Amazônica. A espécie nova difere de B. fredcochui pela presença de uma mancha umeral verticalmente alongada (vs. ausência), linha lateral completa (vs. incompleta), quatro séries de escamas abaixo da linha lateral (vs. três), e menor número de raios ramificados na nadadeira anal (17-21 vs. 22-25), e de B. orcesi pelo maior número de dentes no maxilar (13-14 vs. 5-12), maior comprimento da cabeça (27,9-29,9% vs. 24,3-27,5% do CP), e pelo padrão de colorido (porção inferior da nadadeira dorsal, porção distal da nadadeira pélvica, lobo inferior das nadadeiras caudal e anal com cromatóforos pretos vs. ausência de cromatóforos pretos nas nadadeiras)(AU)

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A new species of Boehlkea is described from rio Japurá, Amazon basin. The new species differs from B. fredcochui by the presence of a vertically elongate humeral spot (vs. absence), complete lateral line (vs. incomplete), four rows of scales below lateral line (vs. three), and lower number of branched anal-fin rays (17-21 vs. 22-25), and from B. orcesi by the higher number of maxillary teeth (13-14 vs. 5-12), greater head length (27.9-29.9% vs. 24.3-27.5% of SL), and by the color pattern (basal half of dorsal-fin, distal portion of pelvic-fin, lower caudal-fin lobe and anal-fin with black chromatophores vs. absence of black chromatophores in the fins).(AU)

Uma nova espécie de Boehlkea é descrita do rio Japurá, bacia Amazônica. A espécie nova difere de B. fredcochui pela presença de uma mancha umeral verticalmente alongada (vs. ausência), linha lateral completa (vs. incompleta), quatro séries de escamas abaixo da linha lateral (vs. três), e menor número de raios ramificados na nadadeira anal (17-21 vs. 22-25), e de B. orcesi pelo maior número de dentes no maxilar (13-14 vs. 5-12), maior comprimento da cabeça (27,9-29,9% vs. 24,3-27,5% do CP), e pelo padrão de colorido (porção inferior da nadadeira dorsal, porção distal da nadadeira pélvica, lobo inferior das nadadeiras caudal e anal com cromatóforos pretos vs. ausência de cromatóforos pretos nas nadadeiras)(AU)

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The species of Percichthys (Percichthyidae) are endemic to southern South America. Some authors have pointed out that the genus includes four valid species, based on the morphology of the head, jaws, and fins. A phylogenetic analysis published by other authors suggests that three of them are morphotypes belonging to the same species, Percichthys trucha (Valenciennes, 1833). The aim of this study is to describe for the first time the morphology of the cephalic seismosensory system of Patagonian perches, and how these characters vary in the three morphotypes, in order to provide morphological elements to analyze the taxonomy of these fish species. Comparisons of the cephalic seismosensory system between juveniles and adults were also conducted. Juvenile and adult specimens were collected in the northwestern Argentinean Patagonia. Specimens were bleached in 5% H2O2 and the canal systems of their cephalic lateral line were filled with hematoxylin. Specimens were deposited in the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Argentina. The cephalic lateral line of the studied specimens is a widened type of canal systems, is not connected to the trunk lateral line, and consists of preopercular-mandibular canal, infraorbital canal, supraorbital canal, temporal canal, supratemporal canal, and a supraorbital commisure. The number of pores increases during the ontogeny, while their diameters decrease. The number, position and size of infraorbital canal pores showed significant differences among morphotypes and juveniles. The interpopulation variation regarding the number, position, and size of pores seems to signal an ongoing process of speciation, which is the result adaptations to different environmental conditions. Our study contributes to the knowledge of the morphology of percichthids and describes for the first time the seismosensory system of temperate perches.(AU)

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The species of Percichthys (Percichthyidae) are endemic to southern South America. Some authors have pointed out that the genus includes four valid species, based on the morphology of the head, jaws, and fins. A phylogenetic analysis published by other authors suggests that three of them are morphotypes belonging to the same species, Percichthys trucha (Valenciennes, 1833). The aim of this study is to describe for the first time the morphology of the cephalic seismosensory system of Patagonian perches, and how these characters vary in the three morphotypes, in order to provide morphological elements to analyze the taxonomy of these fish species. Comparisons of the cephalic seismosensory system between juveniles and adults were also conducted. Juvenile and adult specimens were collected in the northwestern Argentinean Patagonia. Specimens were bleached in 5% H2O2 and the canal systems of their cephalic lateral line were filled with hematoxylin. Specimens were deposited in the Museo Argentino de Ciencias Naturales Bernardino Rivadavia, Argentina. The cephalic lateral line of the studied specimens is a widened type of canal systems, is not connected to the trunk lateral line, and consists of preopercular-mandibular canal, infraorbital canal, supraorbital canal, temporal canal, supratemporal canal, and a supraorbital commisure. The number of pores increases during the ontogeny, while their diameters decrease. The number, position and size of infraorbital canal pores showed significant differences among morphotypes and juveniles. The interpopulation variation regarding the number, position, and size of pores seems to signal an ongoing process of speciation, which is the result adaptations to different environmental conditions. Our study contributes to the knowledge of the morphology of percichthids and describes for the first time the seismosensory system of temperate perches.

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