A new species of Astyanax Baird & Girard (Characiformes: Characidae) from the Rio Paraguaçu basin,Chapada Diamantina,Bahia, Brazil,with comments on bony hooks on all fins

A new species of Astyanax from the Rio Paraguaçu basin, Bahia, Brazil, is described. This new species is distinguished from its congeners known to occur in Brazilian drainages by the presence of small bony hooks on all fins of mature males. Furthermore, the new species can be diagnosed by its colour pattern, which consists of a unique vertically elongated humeral blotch, a conspicuous dark drop‐shaped horizontal blotch over the caudal peduncle, tapering anteriorly and not extending to the median caudal‐fin rays, and by the absence of a conspicuous broad dark midlateral stripe. The new species differs further by having the greatest body depth just anterior to the dorsal‐fin origin, 32–35 perforated scales in the lateral line and a reduced number of branched anal‐fin rays (16–20). Apparently, the new species does not fit into any species complex of Astyanax. The occurrence of bony hooks on all fins of Astyanax is discussed.     

Cytotaxonomy of Astyanax (Characiformes,Characidae) from the Upper Iguaçu River Basin: confirmation of the occurrence of distinct evolutionary units

Taxonomic studies of the genus Astyanax from the Iguaçu River (Brazil) indicate that they may be differentiated into 11 distinct species, some of which have not been formally described and named so for. This study focuses on three of these species, Astyanax sp. B, Astyanax sp. C and Astyanax sp. D from the Upper Iguaçu River Basin. Comparative cytogenetic analyses of C‐banding, Ag‐NORs (silver nitrate stained nucleolar organizer region) and 18S and 5S rDNA corroborate that they are distinct species. A diploid number of 50 chromosomes and similar karyotypic formulae were observed in the three taxa, with the exception of Astyanax sp. D that differs in the number of submetacentric and subtelocentric chromosomes. However, the NOR silver‐staining pattern, the heterochromatic bands (C‐bands) and the mapping of the 18S and 5S rDNA sites in the chromosomes showed divergences between all three species under study, supporting the occurrence of distinct evolutionary units.     

Cytogenetic divergence in two sympatric fish species of the genus Astyanax Baird and Girard, 1854 (Characiformes,Characidae) from northeastern Brazil

The fish genus Astyanax is widespread throughout the Neotropical region and is one of the most species-rich genera of the Characiformes. Cytogenetic studies of Astyanax have revealed marked intra- and interspecific diversity, with the identification of various species complexes. In this report, we describe the karyotypic structure of two sympatric species of Astyanax (Astyanax sp. and Astyanax aff. fasciatus) from the Middle Contas River basin in the northeastern Brazilian state of Bahia. Both species had 2n = 48 but differed in their karyotypic formulae. Small heterochromatic blocks and multiple nucleolar organizer regions (NORs) were identified in both species. Terminal CMA₃⁺/DAPI⁻ signals were observed in Astyanax sp. and A. aff. fasciatus, mostly coincident with NORs. These results show that chromosomal markers can be used to identify species in this fish complex. These markers can provide useful information for evolutionary studies and investigations on the mechanisms of chromosomal diversity in Astyanax.     

Molecular data reveal a diverse Astyanax species complex in the upper Iguaçu River

Astyanax is among the most speciose genera in the Characidae. In this study, molecular markers were used to assess the extent to which some of the commonly recognized Astyanax species of the upper Iguaçu River correspond to natural groups. These results indicate that the diversity of Astyanax has been severely underestimated with several potential cryptic species.     

<Emphasis Type="Italic">Astyanax</Emphasis> <Emphasis Type="Italic">bockmanni</Emphasis> Vari and Castro, 2007: an ambiguous karyotype in the <Emphasis Type="Italic">Astyanax</Emphasis> genus

Despite the widespread distribution of Astyanax bockmanni in streams from Upper Paraná River system in central, southeastern, and southern Brazil, just recently, it has been identified as a distinct Astyanax species. Cytogenetic studies were performed in two populations of this species, revealing conservative features. A. bockmanni shows 2n = 50 chromosomes, a karyotypic formula composed of 10 M + 12SM + 12ST + 16A and multiple Ag-NORs. Eight positive signals in subtelocentric/acrocentric chromosomes were identified by fluorescent in situ hybridization (FISH) with 18S rDNA probes. After FISH with 5S rDNA probes, four sites were detected, comprising the interstitial region of a metacentric pair and the terminal region on long arms of another metracentric pair. Little amounts of constitutive heterochromatin were observed, mainly distributed at distal region in two chromosomal pairs. Additionally, heterochromatin was also located close to the centromeres in some chromosomes. No positive signals were detected in the chromosomes of A. bockmanni by FISH with the As-51 satellite DNA probe. The studied species combines a set of characteristics previously identified in two different Astyanax groups. The chromosomal evolution in the genus Astyanax is discussed.     

Trophic morphology features allow Astyanax endemic species coexistence in a Neotropical river system

Resource partitioning has an essential role in interspecific relations, especially in congener species, which share many morphological traits. In some places, small characids coexist through resource partitioning, which may reduce their interspecific competition. Astyanax species (e.g., Astyanax minor, Astyanax gymnodontus and Astyanax bifasciatus), for example, coexist in different water bodies from the Iguaçu River basin. These species have high phenotypic plasticity and many morphologic specializations that allow them to live in different habitats. Based on evidences that these species modified their feeding habits because of changes in resource availability in Iguaçu River, this study tested two hypotheses: (a) there are differences in head morphology, number of teeth and number of gill rakers among the species of Astyanax; and (b) there are differences in gill arch and gill raker morphology among the species of Astyanax, which may favour their trophic resource partitioning in Iguaçu River. The head morphological traits and quantitative morphological characters were summarized in a principal coordinates analysis (PCoA), and the analysis of similarities (ANOSIM) showed significant differences among species. Gill morphological measurements were analysed through analysis of covariance (ANCOVA), and it also showed significant differences in gill arch and gill raker morphology among species. Therefore, the analysis of ecomorphological traits related to trophic habits revealed some differences that may suggest a tendency of reducing competition for trophic resources in the Iguaçu River basin.     

Reproductive Timing of Fishes in a Tropical Intermittent Stream

Six fish species were studied in an intermittent lowland stream in Trinidad, West Indies for 28 months from 1980 to 1982. They were Gasteropelecus sternicla, Corynopoma riisei, Astyanax bimaculatus, Hemigrammus unilineatus, Corydoras aeneus and Poecilia reticulata. Peaks in GSIs and presence of mature adults and juveniles, as determined from monthly field collections, indicated reproduction coincident with the rainy seasons in all species except Poecilia. Gasteropelecus bred for a short period at the beginning of the main rainy season while Corynopoma, Corydoras and Hemigrammus had extended periods of breeding activity each year coincident with high rainfall. The presence of juveniles suggests that Astyanax also bred during the rainy season. Poecilia reproduced continuously throughout the study period but exhibited discharge-related adult stock fluctuations that may have influenced reproductive activity. Maximum ovarian fecundity correlated with species size suggested body size limitation on fecundity for small species such as Corynopoma and Hemigrammus. Size frequency distributions of oocytes in mature ovaries indicate synchronised ovum maturation in Astyanax and possibly Gasteropelecus, while Hemigrammus, Corynopoma and Corydoras showed evidence of continuous maturation of oocytes and multiple spawning. Prolonged small brood spawning was confirmed in the laboratory for Corynopoma and Hemigrammus and resulted in spawning fecundities up to 11 times greater than ovarian fecundities for Corynopoma. It is concluded that the conditions of intermittency in this stream did not significantly alter the reproductive styles of these species as described for other Neotropical environments, perhaps because of their opportunistic nature. Patterns of spawning for the characoids can be directly related to size and phylogeny.     

Incipient genetic divergence or cryptic speciation? Procamallanus (Nematoda) in freshwater fishes (Astyanax)

Hosts provide the main environmental traits parasites have to deal with, resulting in covariation between both associates at both micro- and macro-evolutionary scales; phylogenetic analyses of highly host-specific parasites have shown that parasite and host phylogeny might be highly congruent, and adaptation of a host species to new environments may lead to concordant changes of their parasites. Procamallanus (Spirocamallanus) neocaballeroi is a highly host-specific parasitic nematode of the Neotropical freshwater fish genus Astyanax in Mexico. One of the host species of the nematode is the emblematic Mexican tetra, A. mexicanus, which exhibits two contrasting phenotypes, a cave-dwelling morph (with troglomorphic features), and the surface-dwelling morph; other congeneric species inhabit rivers and lakes, and some of them occur in sympatry, displaying trophic specializations. Here, we explored the hypothesis that contrasting environments (surface rivers vs cave rivers), and host morphological divergence (sympatric ecomorphs in a lacustrine environment) might result in the divergence of their parasites, even though the hosts maintain a cohesive genetic structure as the same species. To test the hypothesis, several populations of Astyanax spp. were sampled to search for P. (S.) neocaballeroi. The nematode was found in 10 of the 52 sampled sites; two localities corresponded to cave populations. The phylogenetic analysis based on COI sequences yielded three major lineages for P. (S.) neocaballeroi. We found no concordance between the three lineages and the habitat where they occur in Astyanax mexicanus, even considering those living in drastic environmental conditions (caves), or between these lineages and lacustrine ecomorphs of Astyanax aeneus and A. caballeroi occurring in sympatry. Instead, genetic lineages of the nematode exhibit a clearer pattern of host species association and geographical distribution; our results showed that P. (S.) neocaballeroi is experiencing an incipient divergence although the morphological study of lineages shows no conspicuous differences.     

A new species of Astyanax (Characiformes: Characidae) from Costa Rica and Panama,with a key to the lower Central American species of the genus

Astyanax anai, a new species of characid fish, is described from the Sixaola River basin, eastern Costa Rica–western Panama, Central America. The new species can be distinguished from all other congeners by the following combination of characters: premaxillary teeth 4–5 at the inner series and 4–6 at the outer series; maxillary teeth tricuspid, 2–4; predorsal scale series irregular and incomplete, with an unscaled space behind tip of supraoccipital process and 12–14 scales; lateral line scales 34–39; humeral region with a conspicuous black and rounded to horizontally ovate spot and two diffuse brown and vertically elongate bars (the first through the rounded to horizontally ovate spot, the second 2–4 scales behind the first); body depth 36·6–42·3% of standard length (L_S); midlateral stripe formed by a series of 10–14 anteriorly‐directed dermal herringbone, or chevron‐shaped, marks, most apparent in juveniles and in preserved specimens, extending above the lateral line from the black humeral spot or just behind it (from the second vertical bar) to the caudal peduncle; scale rows from lateral line to base of first dorsal‐fin ray 8–9; scale rows from lateral line to base of pelvic fin 7–8; pre‐anal distance 53·9–61·9% of L_S; total anal‐fin elements 29–33; caudal spot elongated, rhomboid or rectangular, with its anterior margin surpassing the middle of the caudal peduncle, usually reaching the anal‐fin insertion, posteriorly covering 4–7 principal caudal‐fin rays and not extending onto the ventral and dorsal margins of the caudal peduncle, covering 3–5 horizontal scale rows. In order to test the phylogenetic relationships of the new taxon in relation to the other North and Central American species of the genus, a new phylogenetic hypothesis based on a reanalysis of the morphological matrix by Schmitter‐Soto (2016) is proposed. A key to the lower Central American (southern Nicaragua to eastern Panama) species of Astyanax is also provided.     

Phenotypic plasticity and karyotype conservation in allopatric populations of Astyanax aff. fasciatus (Teleostei,Characiformes) at the Upper Paraná river basin

Genus Astyanax is known by its wide genetic and morphological diversity. Among the South America's fish, it is one of the most studied groups and with greatest number of characterized population. At the present work, the combined approach of morphological and genetic data analysis was applied. Cytogenetic and morphometric studies were performed in populations of Astyanax aff. fasciatus originating from Paranaíba river and São João river, both from the hydrographic basin of Paranaíba river. Fish originating from a third place at the Mogi‐Guaçu river (Tietê river's basin) and with 2n = 46 chromosomes also went through morphometric analysis. The morphologic data evidenced the populational structuring, following the geographical distribution of the subjects. Cytogenetic data disclosed the same diploid number and karyotype formula for both populations. The other cytogenetic markers comply with the literature. These data show that the two populations of A. aff. fasciatus do not differ among themselves concerning the chromosomal structure, but they structure themselves regarding morphometry. Aspects of evolution of the group are discussed facing this study.     

Morphological patterns of five fish species (four characiforms,one perciform) in relation to feeding habits in a tropical reservoir in south‐eastern Brazil

Described are the ecomorphological attributes of five abundant fish species and their relationships to the feeding ecology in a tropical reservoir in south‐eastern Brazil. A total of 140 individuals were used. All specimens were collected between October 2006 and September 2007. Nine ecomorphological indexes were used and patterns detected by principal components analysis. The carnivorous species (Oligosarcus hepsetus) showed higher relative height of mouth to the mouth width aspect. On the other hand, the herbivorous species (Metynnis maculatus) had a higher compression index to the relative height. Geophagus brasiliensis (perciform) exhibited a larger relative length of the head to the relative length of the caudal peduncle. The two Astyanax species (A. bimaculatus and A. parahybae), although with taxonomic and morphological proximities to each other, exhibited indications of morphological adjustments probably associated to adaptive divergence. Three well‐defined trophic groups were confirmed by the cluster analysis. The ecomorphology was effective in predicting feeding habits and aspects of locomotion, and the eventual consequences of the impoundment may be triggering a morphological divergence between closely related species. The authors hope that knowledge with regard to the effects of these man‐made ecosystems on ichthyofauna ecomorphology will be further elucidated in the coming years, perhaps providing advice for their implementation in future hydropower projects.     

Differential cropping of the caudal fin lobes of prey fishes by the piranha,Serrasalmus spilopleura Kner

Regression analysis of log₁₀ upper and lower caudal lobe area (whole uncropped caudals) against log₁₀ standard length for ten prey species of the piranha showed significant differences in both slope and intercept for only one species (Astyanax fasciatus) although intercepts alone were significantly different for two others (A. bimaculatus and Poecilia vivipara). Caudal lobe — standard length regression statistics were used to generate estimates of caudal lobe loss in cropped prey species and these clearly demonstrated highly significant differential cropping incidences in several species and size categories. Particularly in the Astyanax species, the upper caudal lobe was subject to low cropping loss and the lower caudal lobe to high cropping loss. Differential cropping of caudal fin lobes suggests that piranha initiate their attack from below and behind prey fishes.     

Morphometric variation between two morphotypes within the Astyanax Baird and Girard, 1854 (Actinopterygii: Characidae) genus,From a Mexican tropical lake

Phenotypic variation is important for evolutionary processes because it can allow local adaptation, promote genetic segregation, and ultimately give rise to speciation. Lacustrine systems provide a unique opportunity to study the mechanisms by which sister species can co‐occur by means of ecological segregation. The fish genus Astyanax is characterized by high levels of phenotypic variability, providing an excellent model for the study of local specialization. Here, we analyze the morphological specializations through geometric morphometrics of two sympatric species described as different genera: Bramocharax caballeroi endemic to Lake Catemaco, and the widely distributed Astyanax aeneus. Additionally, we assess the correlation between phenotypic and genetic structure, and the phylogenetic signal of morphological variation. We examined body size and shape variation in 196 individuals and analyzed mitochondrial cytochrome b sequences in 298 individuals. Our results confirm the striking morphological divergence among the sympatric characids. Differences between them were mainly found in the body depth and profile and orientation of the head, where B. caballeroi in contrast with the A. aeneus, presented a fusiform body and an upward mouth. Moreover, different growth trajectories were observed among morphotypes, suggesting that a heterochronic process could be involved in the diversification of our study system. Morphological differences did not correspond with the molecular differentiation, suggesting high levels of homoplasy among the lineages of B. caballeroi morphs. J. Morphol. 275:721–731, 2014. © 2014 Wiley Periodicals, Inc.     

Feeding of Hoplias malabaricus in the wetlands of Dulce river (Córdoba,Argentina)

Hoplias malabaricus behaves as a zoophagous and euryphagic species with a strong tendency to eat fish during its entire life. Fish begin to constitute its main food at approximately 200 mm standard length. Insects are important for fish smaller than 50 mm. Crustaceans are of lesser importance for both size groups."Mojarras" (genus Astyanax), the characin Odontostilbe microcephala, and the catfish Pimelodus albicans are its main prey. The relative importance of each prey type varies with predator length.In high summer more food is eaten by H. malabaricus, and digestion rate, related to the higher temperatures, is also higher. During colder seasons feeding activities decreases markedly.     

Genetic Diversity of the Small Characid Fish Astyanax sp., and its Significance for Conservation

Genetic variations in Astyanax sp. fish from Vila Velha State Park and Tibagi river (Paraná, Brazil) were analyzed by RAPD. Intrapopulational genetic similarity was analyzed at three collection sites. The higher RAPD polymorphism observed at site 3 (Tibagi river) suggests either an overlapping of structured populations or the presence of coexisting morphotypes at this site. Significant p values obtained by homogeneity tests revealed an unequal loci proportion among populations. The significance of similarity coefficients indicated that the differences observed among populations are relevant. These findings provide important information for the management and conservation of the species analyzed and for genetic variability maintenance programs.     

Satellite DNA and chromosomes in Neotropical fishes: methods,applications and perspectives

Constitutive heterochromatin represents a substantial portion of the eukaryote genome, and it is mainly composed of tandemly repeated DNA sequences, such as satellite DNAs, which are also enriched by other dispersed repeated elements, including transposons. Studies on the organization, structure, composition and in situ localization of satellite DNAs have led to consistent advances in the understanding of the genome evolution of species, with a particular focus on heterochromatic domains, the diversification of heteromorphic sex chromosomes and the origin and maintenance of B chromosomes. Satellite DNAs can be chromosome specific or species specific, or they can characterize different species from a genus, family or even representatives of a given order. In some cases, the presence of these repeated elements in members of a single clade has enabled inferences of a phylogenetic nature. Genomic DNA restriction, using specific enzymes, is the most frequently used method for isolating satellite DNAs. Recent methods such as C₀t–1 DNA and chromosome microdissection, however, have proven to be efficient alternatives for the study of this class of DNA. Neotropical ichthyofauna is extremely rich and diverse enabling multiple approaches with regard to the differentiation and evolution of the genome. Genome components of some species and genera have been isolated, mapped and correlated with possible functions and structures of the chromosomes. The 5SHindIII‐DNA satellite DNA, which is specific to Hoplias malabaricus of the Erythrinidae family, has an exclusively centromeric location. The As51 satellite DNA, which is closely correlated with the genome diversification of some species from the genus Astyanax, has also been used to infer relationships between species. In the Prochilodontidae family, two repetitive DNA sequences were mapped on the chromosomes, and the SATH 1 satellite DNA is associated with the origin of heterochromatic B chromosomes in Prochilodus lineatus. Among species of the genus Characidium and the Parodontidae family, amplifications of satellite DNAs have demonstrated that these sequences are related to the differentiation of heteromorphic sex chromosomes. The possible elimination of satellite DNA units could explain the genome compaction that occurs among some species of Neotropical Tetraodontiformes. These topics are discussed in the present review, showing the importance of satellite DNA analysis in the differentiation and karyotype evolution of Actinopterygii.     

Genetics and hybridization in surface and cave Astyanax (Teleostei): a comparison of regressive and constructive traits

Change in ecological conditions, as seen in surface and cave populations of Astyanax (Teleostei), has caused the divergent evolution of a large number of traits like eyes, coloration, taste, lateral line, and different kinds of behaviour like schooling, sleep or feeding posture. Because of the interfertility of surface and cave forms these fish are an exceptional object to study the morphological and genetic basis of the evolution of such complex regressive and constructive traits. Classical crossing analyses and genomic studies are contributing to growing understanding. Both kinds of traits mostly rely on multiple genetic bases and the phenotypic manifestation in the various crosses is similar. The gene effect underlying the phenotypic manifestation may exhibit an exponential increase at differing amounts in the various traits and crosses. Missing or presence of such genetic interaction helps determine whether the variability of eyes or pigmentation exhibited by Astyanax cave fish populations like Micos, is due to a more recent origin or to secondary hybridization with the surface fish. Neither crossing analysis nor QTL mapping revealed that eye reduction is pleiotropically antagonistically related to the increase of taste buds or lateral line sense. Independent inheritance of traits suggests that Astyanax cave fish are subjected to mosaic evolution.     

Hemiodus iratapuru,a new species of Hemiodontidae from the Rio Jari,Amazon Basin,Brazil (Teleostei,Characiformes)

Hemiodus iratapuru, a new species of the Hemiodontidae from the Rio Iratapuru, a left bank tributary of the Rio Jari, Amazon Basin, Brazil, is described. The new species is diagnosed from other species of Hemiodus by modifications in the ectopterygoid, tooth form, scale counts, dorsal‐fin form and colour pattern. The new species is proposed to be related to the Hemiodus quadrimaculatus species group.     

Evolutionary history of the fish genus <Emphasis Type="Italic">Astyanax</Emphasis> Baird &; Girard (1854) (Actinopterygii,Characidae) in Mesoamerica reveals multiple morphological homoplasies

Background  

Mesoamerica is one of the world's most complex biogeographical regions, mostly due to its complex geological history. This complexity has led to interesting biogeographical processes that have resulted in the current diversity and distribution of fauna in the region. The fish genus Astyanax represents a useful model to assess biogeographical hypotheses due to it being one of the most diverse and widely distributed freshwater fish species in the New World. We used mitochondrial and nuclear DNA to evaluate phylogenetic relationships within the genus in Mesoamerica, and to develop historical biogeographical hypotheses to explain its current distribution.