New species of glass knifefish genus Eigenmannia (Gymnotiformes: Sternopygidae) with comments on the morphology and function of the enlarged cephalic lateral-line canals of Sternopygidae.

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.

Anatomy of the mechanosensory lateral line canal system and electrosensory ampullae of Lorenzini in two species of sawshark (fam. Pristiophoridae).

It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano- and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.

Molecular delimitation and taxonomic revision of the wimple piranha Catoprion (Characiformes: Serrasalmidae) with the description of a new species.

A taxonomic revision of wimple piranhas of the genus Catoprion is performed in combination with a molecular analysis using mtDNA. Molecular phylogenetic analyses of 49 specimens using genetic distances, conventional likelihood and four delimitation methods yielded two distinct lineages of Catoprion, with the morphological analyses of 198 specimens of Catoprion corroborating the molecular results. We provide a redescription of Catoprion mento, from the Paraguay, Orinoco, and tributaries of western Amazon basin, keeping Mylesinus macropterus as a junior synonym of C. mento, and the description of Catoprion absconditus n. sp., from the Amazon and Essequibo basins. C. absconditus n. sp. differs from C. mento by the presence of 86-94 perforated scales in the lateral line (vs. 65-86 scales) and the presence of 35-40 circumpeduncular scales (vs. 29-34 scales). The distribution of C. mento follows the Amazonas-Paraguay-Orinoco lowlands, whereas C. absconditus follows the eastern Amazon biogeographic pattern.

Ontogeny and homology of cranial bones associated with lateral-line canals of the Senegal Bichir, Polypterus senegalus (Actinopterygii: Cladistii: Polypteriformes), with a discussion on the formation of lateral-line canal bones in fishes.

The association between lateral-line canals and skull bones in fishes has been the subject of several studies and raised a series of controversies, particularly with regard to the hypothesized role of lateral-line organs (i.e. neuromasts) in osteogenesis and the consequences for hypotheses of homology of the bones associated with lateral-line canals. Polypteridae, a group of freshwater fishes that occupies a key phylogenetic position as the most basal extant lineage of ray-finned fishes (Actinopterygii), provides an interesting model for the study of the relationships between lateral-line canals and skull bones. We describe the development of bones associated with lateral-line canals in the Senegal Bichir, Polypterus senegalus, and use these data to re-address previous hypotheses of homology of skull bones of polypterids. We demonstrate that the lateral-line canals constitute a separate component of the dermatocranium that may interact with a membranodermal component, thereby forming compound bones in the adult. Differences in the interactions between these components determine the characteristics of the development of each independent bone in the skull of adult P. senegalus. Our results shed light on long-standing controversies about the identity of skull bones such as the rostral, preopercle, and sphenotic in Polypteridae, and suggest the presence of an ancestral two-component pattern of formation of bones associated with lateral-line canals in bony fishes. These findings reveal the need to re-address previous hypotheses of homology of bones associated with lateral-line canals in different groups of bony fishes, especially fossil taxa.

Exquisite structure of the lateral line system in eyeless cavefish Sinocyclocheilus tianlinensis contrast to eyed Sinocyclocheilus macrophthalmus (Cypriniformes: Cyprinidae).

In this study, the lateral line systems in Chinese cavefish eyeless Sinocyclocheilus tianlinensis and eyed Sinocyclocheilus macrophthalmus were investigated to reveal their morphological changes to survive in harsh environments. Compared with the eyed cavefish S. macrophthalmus (atypical), the lateral line system in the eyeless cavefish S. tianlinensis (typical) has certain features to adapt to the dark cave environments: the superficial lateral line system in the eyeless species possesses a higher number of superficial neuromasts and more hair cells within an individual neuromast, and the trunk lateral line canal system in S. tianlinensis exhibits larger canal pores, higher canal diameter and more pronounced constrictions. Fluid-structure interaction analysis suggested that the trunk lateral line canal system in the eyeless S. tianlinensis should be more sensitive than that in the eyed S. macrophthalmus. These morphological features of the lateral line system in the eyeless S. tianlinensis probably enhance the functioning of the lateral line system and compensate for the lack of eyes. The revelation of the form-function relationship in the cavefish lateral line system provides inspiration for the design of sensitive artificial flow sensors.

The ontogeny of the lateral line system in Telmatobius atacamensis (Anura, Telmatobiidae).

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.

Potamotrygon marquesi, a new species of neotropical freshwater stingray (Potamotrygonidae) from the Brazilian Amazon Basin.

Potamotrygon marquesi, sp. nov., is described and compared with other species of Potamotrygon occurring in the Amazon Basin. The identity of this new species is supported by an extensive external and internal morphological study including coloration pattern, squamation, skeleton and ventral lateral-line canals. Morphometrics and meristics were used to further distinguish P. marquesi from congeners. Potamotrygon marquesi was first considered to fall within the range of variation found in P. motoro. However, even with an extensive variation in coloration observed in P. motoro, this new species presents a series of autapomorphies that confidently distinguishes it from what is understood as the morphological variation found in P. motoro. Additional morphological characters that diagnose P. marquesi include three angular cartilages, asymmetrical star-shaped denticles, a single regular row of spines on tail dorsum, lateral row of caudal spines near the sting insertion, dorsal disc background in beige and grey mixed with shades of grey and bearing open and closed bicolored rings, among others. Although presenting a gap of distribution along the west-east extension of the Amazon Basin, its diagnostic charactistics are consistent in both recorded regions. Our study supports the need for many morphological characters to robustly distinguish members of Potamotrygoninae considering their extremely variable dorsal disc color pattern.

Convergent evolution of the lateral line system in Apogonidae (Teleostei: Percomorpha) determined from innervation.

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.

Deconstructing an octogenarian misconception reveals the true Corydoras arcuatus Elwin 1938 (Siluriformes: Callichthyidae) and a new Corydoras species from the Amazon basin.

After 80 years of misidentifications, the analysis of the holotype of Corydoras arcuatus plus several non-type specimens attributed to this species allowed its recognition and also revealed a new species, both sharing the following diagnostic features: a long, arched, continuous black stripe that runs parallel to the dorsal profile of the body and extends at least from the anterior margin of the first dorsolateral body plate to the posterior portion of caudal peduncle; absence of transverse black bars on caudal fin; infraorbital 2 in contact with sphenotic and compound pterotic. In addition to these features, C. arcuatus can be distinguished from congeners by having the posterior margin of both dorsal and pectoral spines with laminar serrations directed towards their origins. The new species can be additionally distinguished from its congeners by presenting the following combination of features: ventral surface of trunk entirely or partially covered by relatively large and coalescent platelets; absence of spots or blotches on dorsal fin; and posterior margin of both dorsal and pectoral spines with serrations directed towards their tips. Finally, an identification key to all arc-striped species of Corydoras is provided.

A new species of Piaractus (Characiformes: Serrasalmidae) from the Orinoco Basin with a redescription of Piaractus brachypomus.

Piaractus orinoquensis, a new species of serrasalmid fish, is described from the Orinoco River basin. The new species differs from congeners by having a slenderer body, relatively smaller head and snout, more compressed mid-body, fewer scales above and below the lateral line and diagnostic molecular characters in the coI mitochondrial gene region. We also provide a re-description of Piaractus brachypomus, restricting its geographic distribution to the Amazon River basin. Both species are economically important in their respective basins and need to be independently managed as distinct species.

Sensory ecology of the fish lateral-line system: Morphological and physiological adaptations for the perception of hydrodynamic stimuli.

Fishes are able to detect and perceive the hydrodynamic and physical environment they inhabit and process this sensory information to guide the resultant behaviour through their mechanosensory lateral-line system. This sensory system consists of up to several thousand neuromasts distributed across the entire body of the animal. Using the lateral-line system, fishes perceive water movements of both biotic and abiotic origin. The anatomy of the lateral-line system varies greatly between and within species. It is still a matter of debate as to how different lateral-line anatomies reflect adaptations to the hydrodynamic conditions to which fishes are exposed. While there are many accounts of lateral-line system adaptations for the detection of hydrodynamic signals in distinct behavioural contexts and environments for specific fish species, there is only limited knowledge on how the environment influences intra and interspecific variations in lateral-line morphology. Fishes live in a wide range of habitats with highly diverse hydrodynamic conditions, from pools and lakes and slowly moving deep-sea currents to turbulent and fast running rivers and rough coastal surf regions. Perhaps surprisingly, detailed characterisations of the hydrodynamic properties of natural water bodies are rare. In particular, little is known about the spatio-temporal patterns of the small-scale water motions that are most relevant for many fish behaviours, making it difficult to relate environmental stimuli to sensory system morphology and function. Humans use bodies of water extensively for recreational, industrial and domestic purposes and in doing so often alter the aquatic environment, such as through the release of toxicants, the blocking of rivers by dams and acoustic noise emerging from boats and construction sites. Although the effects of anthropogenic interferences are often not well understood or quantified, it seems obvious that they change not only water quality and appearance but also, they alter hydrodynamic conditions and thus the types of hydrodynamic stimuli acting on fishes. To date, little is known about how anthropogenic influences on the aquatic environment affect the morphology and function of sensory systems in general and the lateral-line system in particular. This review starts out by briefly describing naturally occurring hydrodynamic stimuli and the morphology and neurobiology of the fish lateral-line system. In the main part, adaptations of the fish lateral-line system for the detection and analysis of water movements during various behaviours are presented. Finally, anthropogenic influences on the aquatic environment and potential effects on the fish lateral-line system are discussed.

Canal neuromasts enhance foraging in zebrafish (Danio rerio).

Aquatic animals commonly sense flow using superficial neuromasts (SNs), which are receptors that extend from the body's surface. The lateral line of fishes is unique among these systems because it additionally possesses receptors, the canal neuromasts (CNs), that are recessed within a channel. The lateral line has inspired the development of engineered sensors and concepts in the analysis of flow fields for submersible navigation. The biophysics of CNs are known to be different from the SNs and thereby offer a distinct submodality. However, it is generally unclear whether CNs play a distinct role in behavior. We therefore tested whether CNs enhance foraging in the dark by zebrafish (Danio rerio), a behavior that we elicited with a vibrating rod. We found that juvenile fish, which have only SNs, bite at this rod at about one-third the rate and from as little as one-third the distance of adults for a high-frequency stimulus (50 < f  < 100 Hz). We used novel techniques for manipulating the lateral line in adults to find that CNs offered only a modest benefit at a lower frequency (20 Hz) and that foraging was mediated entirely by cranial neuromasts. Consistent with our behavioral results, biophysical models predicted CNs to be more than an order of magnitude more sensitive than SNs at high frequencies. This enhancement helps to overcome the rapid spatial decay in high-frequency components in the flow around the stimulus. These findings contrast what has been previously established for fishes that are at least ten-times the length of zebrafish, which use trunk CNs to localize prey. Therefore, CNs generally enhance foraging, but in a manner that varies with the size of the fish and its prey. These results have the potential to improve our understanding of flow sensing in aquatic animals and engineered systems.

Intraspecific developmental variation in the life cycle of the Andean Treefrog (Boana riojana): A temporal analysis.

Intraspecific variation during the anuran larval period has been analyzed mainly in relation to the timing of metamorphosis and body size at metamorphosis. However, other traits may vary as well. We examined two developmental series of Boana riojana from the same population in two consecutive years and describe intraspecific variation in larvae of this species. We discuss how variation, if present, may influence its life cycle. We found that both larval series differed in the larval period length, one twice as long as the other. This variation primarily depended on when breeding occurred, metamorphosis was achieved during late spring in both generations and at similar sizes, and only the rate of larval development during premetamorphosis varied extensively between years. This is consistent with thyroid gland activity because when it became active the developmental trajectory became more canalized. No variation of staging sequence occurred in relation to the different durations of the larval period. However, in the long-lasting series we found two different morphs. Also, integument, thyroid gland, skeleton, and testis differentiation events occurred at the same developing stages. In contrast, ovarian differentiation proceeded at the same absolute age in both series. Sexual dimorphism becomes evident within the year after metamorphosis. The intraspecific heterochrony that we describe for the larval development of B. riojana does not lead to phenotypic variation at the end of metamorphosis. We discuss the importance of analyzing growth and development independently. Each proceeds differently in time, but with an interdependence at some point, because size and shape do not vary at the end of metamorphosis.

Mechanosensory system of the lateral line in the subantarctic Patagonian blenny Eleginops maclovinus.

This study describes the cephalic and trunk lateral line systems in Patagonian blenny Eleginops maclovinus juveniles, providing morphological details for pores, canals and neuromasts. Eleginops maclovinus juveniles possess a complete laterodorsal lateral line that extends from the upper apex of the gill opening along the trunk as far as the caudal fin. The lateral line was ramified through pores and canals. The following pores were recorded: four supraorbital pores, with two along the eye border and two on the snout; seven infraorbital pores, with three on the lacrimal bone and four being infraorbital; five postorbital pores, with three along the preopercular border (upper preoperculum branch) and two on the bone curvature (inferior preoperculum branch); and four mandibular pores aligned along the jaw. Furthermore, five narrow-simple and interconnected canals were found (i.e. preopercular, mandibular, supraorbital and infraorbital canals). Histologically, the dorsal lateral line presented thin neuromasts (350 µm) with short hair cells. By contrast, the cranial region presented long, thick neuromasts. Infraorbital and mandibular neuromasts had a major axis length of 260 µm and respective average diameters of 200 and 185 µm. Sensory system variations would be due to a greater concentration of neuromasts in the cranial region, allowing for a greater perception of changes in water pressure. Scarce morphological information is available for the lateral sensory system in Eleginopsidae, particularly compared to Channichthyidae, Bovichthydae, Artedidraconidae and Bathydraconidae. Therefore, the presented results form a fundamental foundation of knowledge for the lateral-line system in juvenile E. maclovinus and provide a basis for future related research in this taxon as well as within the Notothenioidei suborder.

The peripheral nerves of Lepidobatrachus tadpoles (Anura, Ceratophryidae).

The peripheral nervous system of anuran larvae has traditionally been assumed to be largely invariant. Here, we describe the organization of cranial, spinal, and lateral line nerves at different larval stages of Lepidobatrachus spp. based on whole mounts. This is the first detailed description of cranial, spinal, and lateral lines innervation at premetamorphic stages of anuran larvae with notes on temporal variation. We distinguish three sources of morphological variation with respect to other anuran larvae: (a) the loss or reduction of some exclusively larval elements (i.e., the absence of the middle lateral line nerve); (b) spatial changes in the lateral line system (i.e., the supralabial arrangement of component of the anteroventral lateral line nerve); and (c) temporal changes in the disappearance of most of the lateral line system and in the premetamorphic repatterning of the spatial relationships of mandibularis ramus of the trigeminal (V) and hyomandibularis ramus of facial (VII). The innervation of limbs is achieved during late larval stages. Furthermore, comparisons among selected anurans reveal differences in tadpole brain morphology. The spatial and temporal variation found in the peripheral nerves of Lepidobatrachus larvae testifies to previously unappreciated variation in anuran larval morphology.

Neuromast hair cells retain the capacity of regeneration during heavy metal exposure.

The neuromast is the morphological unit of the lateral line of fishes and is composed of a cluster of central sensory cells (hair cells) surrounded by support and mantle cells. Heavy metals exposure leads to disruption of hair cells within the neuromast. It is well known that the zebrafish has the ability to regenerate the hair cells after damage caused by toxicants. The process of regeneration depends on proliferation, differentiation and cellular migration of sensory and non-sensory progenitor cells. Therefore, our study was made in order to identify which cellular types are involved in the complex process of regeneration during heavy metals exposure. For this purpose, adult zebrafish were exposed to various heavy metals (Arsenic, cadmium and zinc) for 72h. After acute (24h) exposure, immunohistochemical localization of S100 (a specific marker for hair cells) in the neuromasts highlighted the hair cells loss. The immunoreaction for Sox2 (a specific marker for stem cells), at the same time, was observed in the support and mantle cells, after exposure to arsenic and cadmium, while only in the support cells after exposure to zinc. After chronic (72h) exposure the hair cells were regenerated, showing an immunoreaction for S100 protein. At the same exposure time to the three metals, a Sox2 immunoreaction was expressed in support and mantle cells. Our results showed for the first time the regenerative capacity of hair cells, not only after, but also during exposure to heavy metals, demonstrated by the presence of different stem cells that can diversify in hair cells.

Morphology and hydro-sensory role of superficial neuromasts in schooling behaviour of yellow-eyed mullet (Aldrichetta forsteri).

The lateral line system is a mechanosensory organ found in all fish species and located on the skin or in subdermal canals. The basic functional units are superficial and canal neuromasts, which are involved in hydrodynamic sensing and cohesion in schooling fish. Yellow-eyed mullet (Aldrichetta forsteri) are an obligate schooling species found commonly in shallow coastal areas of New Zealand and Australia. Schooling is a fundamental part of their behavioural repertoire, yet little is known about the structure or functionality of the lateral line in this species. We used scanning electron microscopy to characterise the morphology of trunk superficial neuromasts. We then took a multi-sensory approach and conducted behavioural experiments comparing school structure in groups of fish with and without fully functioning lateral lines, under photopic and scotopic conditions. A highly developed hydro-sensing system exists on the trunk of yellow-eyed mullet consisting of superficial neuromasts containing hundreds of hair cells aligned, with respect to their most sensitive axis, in a rostrocaudal direction. Without functioning superficial neuromasts, schooling behaviour was disrupted under both photopic and scotopic conditions and the ability to detect stationary objects decreased. Results highlight the importance of this component of the lateral line system to schooling behaviour.

Form and function of the teleost lateral line revealed using three-dimensional imaging and computational fluid dynamics.

Fishes sense weak water motion using the lateral line. Among the thousands of described fish species, this organ may differ in size, shape and distribution of individual mechanoreceptors or lateral line canals. The reasons for this diversity remain unclear, but are very likely related to habitat preferences. To better understand the performance of the organ in natural hydrodynamic surroundings, various three-dimensional imaging datasets of the cephalic lateral line were gathered using Leuciscus idus as representative freshwater teleost. These data are employed to simulate hydrodynamic phenomena around the head and within lateral line canals. The results show that changes in canal dimensions alter the absolute stimulation amplitudes, but have little effect on the relation between bulk water flow and higher frequency signals. By contrast, depressions in the skin known as epidermal pits reduce bulk flow stimulation and increase the ratio between higher-frequency signals and the background flow stimulus.

Functional diversity of the lateral line system among populations of a native Australian freshwater fish.

Fishes use their mechanoreceptive lateral line system to sense nearby objects by detecting slight fluctuations in hydrodynamic motion within their immediate environment. Species of fish from different habitats often display specialisations of the lateral line system, in particular the distribution and abundance of neuromasts, but the lateral line can also exhibit considerable diversity within a species. Here, we provide the first investigation of the lateral line system of the Australian western rainbowfish (Melanotaenia australis), a species that occupies a diversity of freshwater habitats across semi-arid northwest Australia. We collected 155 individuals from eight populations and surveyed each habitat for environmental factors that may contribute to lateral line specialisation, including water flow, predation risk, habitat structure and prey availability. Scanning electron microscopy and fluorescent dye labelling were used to describe the lateral line system in M. australis, and to examine whether the abundance and arrangement of superficial neuromasts (SNs) varied within and among populations. We found that the SNs of M. australis were present in distinct body regions rather than lines. The abundance of SNs within each body region was highly variable, and also differed among populations and individuals. Variation in SN abundance among populations was best explained by habitat structure and the availability of invertebrate prey. Our finding that specific environmental factors explain among-population variation in a key sensory system suggests that the ability to acquire sensory information is specialised for the particular behavioural needs of the animal.

The Laterosensory Canal System in Epigean and Subterranean Ituglanis (Siluriformes: Trichomycteridae), With Comments About Troglomorphism and the Phylogeny of the Genus.

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.