Characidae Research Articles

Phylogenomics of Characidae, a hyper-diverse Neotropical freshwater fish lineage, with a phylogenetic classification including four families (Teleostei: Characiformes)

Abstract Neotropical tetras of the family Characidae form the largest and most taxonomically complex clade within the order Characiformes. Previous phylogenetic relationships concur on the recognition of four major subclades, whereas knowledge on intergeneric and interspecific relationships remains largely incomplete or nonexistent. We sampled 575 specimens of 494 species and 123 genera classified in Characidae, generated new molecular data of ultraconserved elements (UCEs), and used likelihood and Bayesian analyses. The phylogeny (1348 UCE loci: 538 472 bp) yielded clades with unprecedented resolution at species- and genus-levels, allowing us to propose a new classification of former Characidae into four families: Spintherobolidae, Stevardiidae, Characidae, and Acestrorhamphidae. The family Stevardiidae includes nine subfamilies: Landoninae, Xenurobryconinae, Glandulocaudinae, Argopleurinae, Hemibryconinae, Stevardiinae, Planaltininae, Creagrutinae, and Diapominae. The family Characidae includes five subfamilies: Aphyocharacinae, Cheirodontinae, Exodontinae, Tetragonopterinae, and Characinae. The family Acestrorhamphidae congregates 15 subfamilies: Oxybryconinae, Trochilocharacinae, Stygichthyinae, Megalamphodinae, Stichonodontinae, unnamed subfamily, Stethaprioninae, Pristellinae, Jupiabinae, Tyttobryconinae, Hyphessobryconinae, Thayeriinae, Rhoadsiinae, Grundulinae, and Acestrorhamphinae. The phylogeny resolves intergeneric relationships and supports revalidation of Myxiops, Megalamphodus, Ramirezella, Holopristis, and Astyanacinus, synonymy of Aphyodite, Genycharax, and Psellogrammus, and expansion of Cyanogaster, Makunaima, Deuterodon, Hasemania, Hemigrammus, Bario, Ctenobrycon, and Psalidodon. The phylogeny opens avenues for new systematic reviews and redefinitions of included genera.

Comparative cytogenetics of microsatellite distribution in two tetra fishes Astyanax bimaculatus (Linnaeus, 1758) and Psalidodon scabripinnis (Jenyns, 1842).

The main cytogenetic studies of the Characidae family comprise the genera Astyanax and Psalidodon involving the use of repetitive DNA probes. However, for the microsatellite classes, studies are still scarce and the function of these sequences in the genome of these individuals is still not understood. Thus, we aimed to analyze and compare the distribution of microsatellite sequences in the species Astyanax bimaculatus and Psalidodon scabripinnis. We collected biopsies from the fins of A. bimaculatus and P. scabripinnis to perform cell culture, followed by chromosome extraction, and mapped the distribution of 14 microsatellites by FISH in both species. The diploid number observed for both species was 2n = 50, with an acrocentric B microchromosome in A. bimaculatus and a metacentric B chromosome in P.scabripinnis. Regarding FISH, 11 probes hybridized in the karyotype of A. bimaculatus mainly in centromeric regions, and 13 probes hybridized in P.scabripinnis, mainly in telomeric regions, in addition to a large accumulation of microsatellite hybridization on its B chromosome. Comparative FISH mapping of 14 microsatellite motifs revealed different patterns of distribution both in autosomes and supernumerary chromosomes of A.bimaculatus and P. scabripinnis, suggesting independent evolutionary processes in each of these species, representing excellent data on chromosome rearrangements and cytotaxonomy.

A ictiofauna da bacia do Rio Potiritá: avaliando o status de conservação em uma área de mineração na Amazônia Oriental

Abstract Aim Considering the importance of knowing the organisms that make up the environments impacted by human activities, we aimed to create an inventory of the ichthyofauna of a bauxite mining area in the Eastern Amazon in this work. Methods Specimens were collected with sieves, trawls, and gill nets at 37 points in rivers and streams during two expeditions (July 2017 and September and October 2017). After euthanasia and laboratory processes, we identified each individual to the lowest possible taxonomic level, and samples were deposited in scientific collections. We analyzed the conservation status of the species on state, national, and international lists. Results A total of 109 species were identified, belonging to 28 families and six orders, emphasizing the Characiformes order (57 species) and the Characidae family (22 species). We identified two new species, and none are threatened with extinction. Conclusions The high species richness recorded in the Potiritá River basin is noteworthy, considering its relatively small area. This diversity should be considered in future environmental impact studies and in monitoring the ichthyofauna in areas affected by human activities.

Peixes de afluentes do Rio Branco, Município de Caracaraí, Estado de Roraima, norte do Brasil

Abstract The Amazon has the richest freshwater ichthyofauna of the planet, with tens of new species being described annually. Although studies on Amazonian fish in the literature are increasingly common recently, there are still significant gaps concerning primary data on the ichthyofauna. One such gap is the state of Roraima and its main drainage, Rio Branco. There is a single book published in 2007 on fishes of Rio Branco, and although it presents a rather complete list of over 580 species known until then, the information is now a little outdated and many species found in some of its affluents are not listed in the book. Due to the scarcity of published data on the fish diversity of Roraima and taking into account that ichthyofaunal surveys are important tools towards freshwater conservation, we carried out an inventory of the ichthyofauna in the region of Caracaraí (RR) in 18 sampling sites including seven affluents of both left and right margins of Rio Branco. We recorded a total of 64 species of 41 genera and 18 families of five orders that occur in the Neotropical region, representing more than 11% of the species previously registered in the book for the entire Rio Branco basin. Twelve species were added to the list presented in the book, with four representing first records for the basin, one of them a new record for Brazil. Two of the 64 species are putative new taxa in need of further taxonomic studies. The order with the highest diversity was Characiformes (40 species), with highlights for the family Characidae (24 of these species), followed by Cichliformes (11 species) and Siluriformes (9 species). The richest collecting sites had 23 species, and the least rich site had only two species. Hyphessobrycon bentosi and Nannostomus marginatus occurred in more than 60% of the sites. There has been a significant difference in the exclusive ichthyofauna from affluents of both margins of Rio Branco, with the number of exclusive species in left margin tributaries approximately five times higher. Results presented herein complement data from the literature regarding the still poorly known ichthyofauna from Roraima.

Stream fish assemblages in the Eastern Amazon: the role of small tetras (Characidae) in alpha diversity and taxonomic structure

Abstract Wallacean shortfalls in knowledge about biodiversity, especially in the Amazon biome, can only be addressed by increasing sampling efforts in focal areas. The objective of this study was to describe the fish fauna of streams associated with four protected areas in the Eastern Amazon. These areas include the Tapajós (Parque Nacional da Amazônia, Parque Nacional do Jamanxim) and Trombetas drainages (Floresta Nacional Saracá-Taquera), and Tapajós/Xingu interfluve (Reserva Biológica Nascentes da Serra do Cachimbo), state of Pará, Brazil. In the 99 stream reaches surveyed, 176 fish species were recorded. Almost a third of the species and specimens belong to the Characidae family, predominantly represented by small tetras (known as piabasor lambaris). One threatened species (Harttia dissidens) was registered. Of the total richness, 24 species were singletons and associated with specific habitats. The highest taxonomic distinctness was observed for Floresta Nacional Saracá-Taquera, while streams within the Parque Nacional da Amazônia exhibited the greatest taxonomic distinctness variation. Compared to existing records in scientific collections covering stream fish fauna in watersheds of up to 4,300 hectares in Pará, our study added the record of eight other genera and identified relevant areas for additional surveys.

The Complete Mitogenome of Amazonian Hyphessobrycon heterorhabdus (Characiformes: Characidae) as a Valuable Resource for Phylogenetic Analyses of Characidae

Hyphessobrycon heterorhabdus (Ulrey, 1894), popularly known as ‘Flag Tetra’ in English speaking countries, belongs to the genus Hyphessobrycon of the family Characidae, and is widely present in the eastern Amazon basin. Here, using Illumina sequencing, we report the complete mitogenome sequence of H. heterorhabdus. Overall, the mitogenome has 17,021 bp, containing 13 protein-coding, 22 tRNA, and 2 rRNA genes. Non-ambiguous nucleotide compositions of the H. heterorhabdus mitogenome are A: 29.2%, T: 29.4%, G: 15.6%, and C: 25.8%. As recently indicated, the phylogenetic analyses did not support four separate genera (Hemigrammus, Hyphessobrycon, Moenkhausia, and Psalidodon) of Characidae. Understanding the H. heterorhabdus mitogenome is important for taxonomic purposes as well as for the molecular characterization of environmental pollutants. Thus, the mitogenome described here will be a valuable resource for studies on environmental changes, evolutionary genetics, species delimitation, and phylogenetic analyses in Characidae.

Phylogenomics of trans-Andean tetras of the genus Hyphessobrycon Durbin 1908 (Stethaprioninae: Characidae) and colonization patterns of Middle America.

Hyphessobrycon is one of the most species rich and widely distributed genera in the family Characidae, with more than 160 species ranging from Veracruz, Mexico to Mar Chiquita Lagoon in Buenos Aires, Argentina. The majority of Hyphessobrycon diversity shows a cis-Andean distribution; only nine species are trans-Andean including H. compressus (Meek 1908). It is well established that Hyphessobrycon is not monophyletic but it has been suggested that natural groups can be identified within the larger Hyphessobrycon species group. In this study, we tested the monophyly of trans-Andean species of Hyphessobrycon and investigated the placement of H. compressus. We inferred the first phylogenomic hypothesis of trans-Andean Hyphessobrycon that includes nearly complete taxonomic sampling (eight of nine valid species) using ultraconserved elements (UCEs). We analyzed 75% (1682 UCEs), 90% (1258 UCEs), and 95% (838 UCEs) complete data matrices, and inferred phylogenomic hypotheses under concatenation and coalescent approaches. In all cases, we recovered the monophyly of trans-Andean Hyphessobrycon inclusive of H. compressus, strong support for three species groups, and evidence of cryptic diversity within the widespread H. compressus and H. condotensis. We used our phylogenomic hypothesis to investigate the biogeographic history of Hyphessobrycon in Middle America. Our ancestral range estimation analysis suggests a single event of cis- to trans-Andean colonization followed by stepwise colonization from the Pacific slope of northwestern South America (Chocó block) to northern Middle America (Maya block). Our work supports the recognition of the trans-Andean species as Hyphessobrycon sensu stricto and provides an evolutionary template to examine morphological characters that will allow us to better understand the diversity of Hyphessobrycon in Middle America.

Molecular characterization of Astyanax species (Characiformes: Characidae) from the upper Paraguaçu River basin, a hydrographic system with high endemism

Abstract Molecular tools have been employed to improve the knowledge about freshwater Neotropical fishes. Such approaches supporting studies of groups including species complexes such as Astyanax, one of the most diversified and taxonomically complex genus of the family Characidae. Here, we employed species delimitation analyses in four Astyanax species described for the upper Paraguaçu River basin, a drainage within Northeastern Mata Atlântica freshwater ecoregion with high endemism. We implemented single and multilocus approaches based on two mitochondrial and one nuclear markers. Cytochrome c Oxidase I sequences previously available for Astyanax species were also added to our dataset. The single locus analyses showed A. epiagos, A. rupestris, and A. aff. rupestris as different Molecular Operational Taxonomic Units (MOTUs), while A. brucutu and A. lorien were grouped. However, the multilocus approach distinguished these two species and showed congruence for the remaining single locus results. Astyanax aff. rupestris was separated into two MOTUs using both approaches, highlighting the need for an integrative taxonomic revision including A. aff. rupestris. These findings contribute to a better understanding of the diversity of this fish group in the upper Paraguaçu, identifying hidden diversity and reinforcing the relevance of this hydrographic system as a notable hotspot for ichthyofauna biodiversity endemism.

Investigation on the influence of inherent AAEMs on gasification reactivity of solid digestate char

Char reactivity usually determines the overall efficiency of the entire gasification process, while the presence of the alkali and alkaline earth metals (AAEMs) has a catalytic effect on char gasification. In this study, the influence of inherent AAEMs in the gasification behaviour of char was investigated. The char sample was prepared through the pyrolysis of solid digestate derived from anaerobic co-digestion of silage and dairy cattle slurry. The raw char and HCl-washed char were characterized by elemental analyzer, ICP-OES, SEM and XRD to explore their structural changes. HCl-char loses weight in the temperature range of 440–620 °C, and the weight loss percentage is significantly higher than that of char. Ash content of char is reduced by half after a pickling process. AAEMs are largely removed after char acid pickling, resulting in an increase in activation energy of the gasification reaction and a decrease in gasification reactivity, resulting in the gasification reaction time of HCl-char longer than char. Water-soluble AAEM and ion-exchange AAEM affect the evolution of carbon structure, which directly lead to char reactivity during the gasification reaction. As the carbon is consumed, the carbon microcrystalline structure of the residual carbon tends to be ordered, resulting in fewer active free carbon sites for the gasification reaction. Kinetic analysis showed that the loss and deactivation of AAEMs after char acid washing increased the average activation energy Ea by 115.76 KJ/mol compared with the original char.

Sperm phylogeny of Characidae (Teleostei, Characiformes)

AbstractThe phylogeny of the very diverse Neotropical fish family Characidae has been the subject of several recent contributions based on morphological characters, molecular data or both in combined analyses. In cases of conflict between these kinds of data, resolution by combined analyses most often tends to agree with the molecular evidence, given the disproportionate number of characters it contains in comparison with morphological datasets. This happens especially after the advent of massive DNA sequencing methods. In this contribution, we present the most comprehensive set of characters from sperm and spermiogenesis of the Characidae. Since these traits are not expected to be functionally correlated with the general morphology or molecular markers, we consider them a third source of data. We provide a phylogenetic analysis from a combined dataset of seven molecular markers (6444 characters), general morphology (520 characters) and reproductive features (94 characters) coded for 165 species of characiform fishes. Parsimony analyses were done under extended implied weighting under 30 different combinations of weighting schemes and strengths. Most parsimonious trees from two different weighting conditions were selected as representative samples of the obtained topologies, in order to evaluate the performance of the reproductive characters. One of these hypotheses is more conservative regarding the currently accepted phylogenies and the other is the most parsimonious tree that we found as the best correlated with the morphological data. Reproductive characters are shown to be more homoplastic than general morphology and DNA, but provided synapomorphies for 23–24 nodes that had no morphological synapomorphies, justifying their use in phylogenetic analyses. Also, in combination with data from general morphology and considering details of the phylogenetic analysis, they showed to have the potential to challenge well‐established hypotheses based on molecular data.

Effects of temperature on food intake and the expression of appetite regulators in three Characidae fish: The black-skirted tetra (Gymnocorymbus ternetzi), neon tetra (Paracheirodon innesi) and Mexican cavefish (Astyanax mexicanus)

The Characidae family of fish is composed of commercially important species for which little is known about the regulation of feeding. Fish are ectotherms so that their body temperature fluctuates with the temperature of the surrounding water. Changes in water temperature can thus have major effects on the physiology of fish, in particular their feeding. The mechanisms by which appetite is influenced by changes in temperatures in fish remain unclear. In this study, we examined the effects of temperature on feeding behavior, food intake and the expression of appetite regulators in three characid fish (black tetra, neon tetra and cavefish) by submitting them to four different temperatures for 2 weeks (20°C, 24°C, 28°C, 32°C). In all species, food intake increased with increasing temperature. In neon and black tetras, increasing temperatures decreased expressions of orexin and leptin and increased that of cocaine and amphetamine regulated transcript (CART). In cavefish, temperature had no effect on brain orexin, leptin or CART. In all three species, higher temperatures induced increases in intestine expression of cholecystokinin (CCK), but no effects were seen for intestine ghrelin and peptide YY expressions. Our results show that temperature affects feeding in Characidae fish and induces species-specific changes in the expression of appetite regulators.

Ultrastructural and immunohistochemical characteristics of the olfactory organ cardinal tetra, Paracheirodon axelrodi (Characiformes: Characidae).

The cardinal tetra Paracheirodon axelrodibelongs to the family Characidae, an economically important and morphologically diverse family of fishes. Information on the olfactory system of this species is scattered and scarce. Among teleost fishes, differences exist in the shape, number, and arrangement of the olfactory lamellae, in the distribution of the sensory and nonsensory epithelium, as well as in the abundance of various receptor cell types. Here, an anatomical and morphological description of the olfactory system was carried out using light microscopic histology, immunohistochemistry, scanning electron microscopy, and transmission electron microscopy. P. axelrodi is a ditremous and isosmat species. It has an arrow-shaped olfactory rosette arrangement. The olfactory epithelium is covering the 12-14 lamellae of the olfactory rosette and, using scanning electron microscopy, we observed that the apical surface of the olfactory epithelium carries a dense layer of mucus. Based on the histological, immunohistochemical, and ultrastructural descriptions, all characteristic sensory and nonsensory cell types of the olfactory epithelium of teleost fish were identified. Three types of olfactory receptor neurons were identified: ciliated, microvilli, and crypt cells. The distribution of sensory and nonsensory cell types is like that described in Aphyocharax anisitsi, another species of the Characidae family. A. anisitsi inhabits slow-flowing water bodies with high-density vegetation such as P. axelrodi.

Mitogenome of Knodus borki (Cypriniformes: Characidae): genomic characterization and phylogenetic analysis.

The taxonomic status of Knodu in the family Characidae is not yet clear. This study aimed to address this by sequencing and annotating Knodu borki Zarske, 2008. K. borki Zarske, 2008 was sequenced using a Hiseq platform and the complete mitogenome was assembled in SPAdes v3.15.2 and SOAPdenovo2 v.2.01. The mitogenome of K. borki from Guangzhou, the first sequenced species of the genus Knodu, is 16,837bp in length and contains 13 protein-coding genes (PCGs), two ribosomal (r) RNAs, 22 transfer (t) RNAs, and one D-loop. Among these 37 genes, 28 are encoded by the heavy strand, while nine are encoded by the light strand. Twenty-one of the tRNAs can form typical cloverleaf secondary structures, except tRNA-Ser1, which lacks dihydrouridine arms. All PCGs have the same start codon (ATG), with the exception of COI (GTG). Four PCGs (ND1, ATP8, ND4L, and ND5) have TAA as the stop codon, ND6 has TAG as the stop codon, COI has AGG as the stop codon, and the remaining seven genes have incomplete stop codons of TA-/T-(ND2, COII, COIII, ND3, ND4, and Cyt b as T-, ATP6 as TA-). Phylogenetic analysis showed that K. borki belongs to the family Characidae. Our findings demonstrate that K. borki belongs to the family Characidae, due to consistency with the morphological identification. This study provides molecular information for further research on the phylogeny of the genus Knodus and for analyses of the taxonomic status of Characidae.

First determination and analysis of the complete mitochondrial genome of X-ray tetra Pristella maxillaris (Ulrey, 1894) (Actinopteri, Characidae)

The complete mitochondrial genome of the X-ray tetra (Pristella maxillaris, Ulrey, 1894) was determined by using next-generation sequencing technology, and its mitochondrial genome characteristics were analyzed. The sequence total length was 16,753 bp, and the A + T content was 57.44%. The position and composition of the 37 genes were consistent with those of other Characidae species in this family. There are 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and one control region. Except for ND2 and COX1, which use ATT and GTG as start codons, respectively, all other protein-coding genes use ATG as the start codon. COX1 uses AGG as the stop codon; ATP6 and COX3 use incomplete TA as the stop codon; COX2 and ND4 use incomplete T as the stop codon; ATP8 uses TAG as the stop codon, and the other seven protein-coding genes use TAA as the stop codon. Based on the concatenated nucleotide sequences of 13 protein-coding genes from 18 Characidae species, phylogenetic analysis revealed that P. maxillaris belongs to the family Characidae and is most closely related to Hyphessobrycon amandae. Determining the mitogenomes of P. maxillaris improves our understanding of the phylogeny and evolution of Characidae.

Divergence times of the Rhoadsia clade (Characiformes: Characidae)

Abstract The family Characidae is the most diverse group of fishes in the Neotropics with challenging systematics. The three genera Carlana, Parastremma, and Rhoadsia, formerly considered the subfamily Rhoadsiinae, are now included in the subfamily Stethaprioninae. Previous phylogenetic analyses did not include all genera of Rhoadsiinae, specifically Parastremma. Here, we estimated the phylogenetic relationships and divergence times of the genera of Rhoadsiinae (the Rhoadsia clade) relative to the most representative genera of the Characidae. We used six molecular markers from the mitochondrial and nuclear genome to estimate the phylogeny and divergence times. We confirmed the monophyly of the Rhoadsia clade. Furthermore, we estimated that the Central American genus Carlana and the western Colombian genus Parastremma diverged approximately 13 Mya (95% HPD 8.36–18.11), consistent with the early-closure estimates of the Isthmus of Panama (~15 Mya). The genus Rhoadsia, endemic to Western Ecuador and Northern Peru, was estimated to originate at around 20 Mya (95% HPD 14.35–25.43), consistent with the Andean uplift (~20 Mya).

Complete mitogenome of Gymnocorymbus ternetzi (Characiformes: Characidae: Gymnocorymbus) and phylogenetic implications

Gymnocorymbus ternetzi belongs to the genus Gymnocorymbus in the family Characidae, and is mainly distributed in southern Brazil. Herein, we report the complete mitogenome of G. ternetzi using Illumina sequencing data. The mitogenome is 17,999 bp in length and contains 13 protein-coding genes, 22 transfer RNA genes, and 2 ribosomal RNA genes. Phylogenetic analysis of G. ternetzi and 18 related species within Characidae indicates that G. ternetzi clusters within the family Characidae. The data provide useful genetic information for future studies on the taxonomy, phylogeny, and evolution of Characidae species.

Osteology of Tucanoichthys tucano Géry and Römer, an enigmatic miniature fish from the Amazon basin, Brazil (Teleostei: Characiformes: Characidae)

Miniaturization, the evolution of extremely small adult body size, is a common phenomenon across the lineages of freshwater fishes, especially in the Neotropics where over 200 species are considered miniature (≤26 mm in standard length [SL]). Close to 30% of all miniature Neotropical freshwater fishes belong to the family Characidae, several of which are of uncertain phylogenetic placement within the family. We investigate the skeletal anatomy ofTucanoichthys tucano, a species of uncertain phylogenetic position from the upper Rio Negro basin, reaching a maximum known size of 16.6 mm SL. The skeleton ofTucanoichthysis characterized by the complete absence of ten skeletal elements and marked reduction in size and/or complexity of others, especially those elements associated with the cephalic latero-sensory canal system. Missing elements in the skeleton ofTucanoichthysinclude those that develop relatively late in the ossification sequence of the non-miniature characiformSalminus brasiliensis, suggesting that their absence inTucanoichthyscan be explained by a simple scenario of developmental truncation. A number of the reductions in the skeleton ofTucanoichthysare shared with other miniature characiforms, most notably species ofPriocharaxandTyttobrycon, the latter a putative close relative ofTucanoichthysbased on molecular data.

Museum specimens reveal a rare new characid fish genus, helping to refine the interrelationships of the Probolodini (Characidae: Stethaprioninae)

(Received 7 July 2021; accepted 23 September 2021) Two new characid fish species are described from the upper rio Tocantins basin, Chapada dos Veadeiros, Goiás State, Brazil. Both species were discovered among specimens in museum collections. Relationships of taxa were evaluated in a more comprehensive phylogenetic analysis utilizing the largest dataset available of molecular and morphological data for the family Characidae. The two species were recovered as sister species and described in a new genus, closely related to Erythrocharax and Phycocharax. Dinotopterygium gen. nov. is distinguished from all other characid genera by the unique combination of ten synapomorphies, including the unique anal-fin morphology with a small number of branched anal-fin rays (13-16). Dinotopterygium uniodon sp. nov. and D. diodon sp. nov. differ by the number of tooth series in the premaxillary bone (one or two) and number of tooth cusps (7 or 5). The additional phenotypic variation for a taxonomically informative character within the Characidae through the discovery of new forms has helped to refine the interrelationship of the tribe Probolodini (Characidae: Stethaprioninae). The discovery of these new and possibly critically endangered species emphasizes the importance of museum collections for understanding biodiversity past and present. http://zoobank.org/urn:lsid:zoobank.org:pub:E0FD8207-590B-4FF7-B9CA-FD481A7F8B0E

EVOLUÇÃO DA ICTIOFAUNA DE RIACHOS SUL-AMERICANOS (CASTRO, 1999) REVISITADO APÓS MAIS DE DUAS DÉCADAS

A little more than 20 years after the first publication of Castro (1999), the knowledge of the South American freshwater ichthyofauna, especially that of Brazil, has increased dramatically. This increase occurred both in terms of knowledge of its taxonomic diversity - in 1999, based on various sources in the scientific literature, a total of 2,800 species of South American freshwater fish was estimated, and a total of near 3,500 species it is currently known from Brazil alone - as to the knowledge of its evolution and also ecology. Consequently, all the hypotheses originally proposed in that paper are reexamined and critically discussed here considering this new knowledge accumulated in the past nearly two decades. Although the original 1999 hypothesis that the small adult size of their respective species is a general evolutionary pattern shared by the South American stream ichthyofauna has been firmly corroborated by several studies carried out in many regions of Brazil, the different patterns associated with most of the species of stream fish originally proposed are discussed in this chapter in the light of the new accumulated knowledge about their biology and ecology. Likewise, the possible role of heterochrony in their respective evolution is critically analyzed in the context of the great advance that has occurred in understanding the phylogenetic relationships of component taxa of freshwater neotropical ichthyofauna, using mainly the family Characidae as a possible model. Finally, a recent intriguing idea of the role of respiratory physiology in determining both the maximum size of teleost fish and their patterns of environmental occupation is examined in relation to its possible effect in the evolution of South American stream ichthyofauna.

Characithecium spp. (Monogenea: Dactylogyridae) from Astyanax bimaculatus (Characiformes: Characidae) in Northeast Brazil, with Description of a New Species.

To date, seven species of Characithecium Mendonza-Franco, Reina and Torchin, 2009 (Monogenea, Dactylogyridae) are valid, parasitizing mainly fishes of the family Characidae (Characiformes) in the Neotropical region. During a parasitological study of fishes in the Batateiras River and Carás stream, Ceará state, Brazil, two species of Characithecium were collected from the gills of Astyanax bimaculatus Linnaeus, 1758 (Characidae). The purpose of the present study is to describe a new species of monogenean of the genus Characithecium and report Characithecium costaricensis Mendoza-Franco, Reina and Torchin, 2009 in A. bimaculatus, in Brazil. Monogeneans were isolated from the gills and stored in 70% ethanol, mounted in Gray and Wess' medium or and in a mixture of glycerin ammonium picrate (GAP) to study sclerotized structures. Morphological analyses were performed with a computerized image analysis system with differential interference contrast (DIC). The drawings were obtained with the aid of a camera lucida mounted on a Leica DMLS microscope. Characithecium bifurcuprolatum n. sp. differs from its congenerics by the morphology of the accessory piece having a ventral unit articulated to cirrus base, a non-articulated dorsal and mid-ventral, and a sclerotized vaginal vestibule. Characithecium costaricensis was described from Astyanax aeneus (Günther, 1860) (Characidae) in Central America, and the present finding represents a new geographical and host records in Brazil. Furthermore, we observed the presence of a membrane at the base of the cirrus not mentioned in the original description. Our findings increase to eight the number of known species of the genus Characithecium parasitizing characids in neotropics. We verified some additional characteristics present in the two species studied, such as the presence of a membrane at the base of the cirrus, an accessory piece with two subunits (an articulated ventral and a dorsal non-articulated) and the presence of sclerotized vaginal vestibule.