Corydoras Paleatus Research Articles

Karyotype reexamination of Corydoras paleatus (Siluriformes) and a review of the cytogenetics of genus with a focus on the ribosomal genes

The subfamily Corydoradinae is the second largest among the callictids, comprising three genera, with Corydoras Lacépède, 1803 being the largest in the number of species. The genus Corydoras has been divided into five groups of species based on differences in diploid number, chromosomal morphology, and DNA content. Chromosome studies can provide crucial details on population differentiation. To better understand the diversification that occurs in this fish group, the current study based on such markers, presents data from a population of Corydoras paleatus from the first plateau of Paraná, putting them in a comparative scenario. The specimens studied has 2n=44 chromosomes with a karyotypic formula of 18m+26sm. Although conserved, this karyotypic structure shows variation in other populations of C. paleatus already studied, a consequence of chromosomal rearrangements that modify the morphology of chromosomes without modifying the 2n, such as centromeric repositioning. C-banding revealed conspicuous pericentromeric markings in metacentric pairs 4 and 8 and in submetacentric pairs 10 and 14, whose bands have been considered a chromosomal marker not only for C. paleatus but also for the genus. Fluorescent in situ hybridization (FISH) showed the major rDNA (45S) in the terminal region of the long arm of metacentric pair 5. Such location has already been described in other populations of C. paleatus, as they have also been mapped in short arms and with multiple patterns. The present study also provides a review of the genus Corydoras regarding the 2n, karyotypic formula and mainly regarding the number and location of the 45S and 5S rDNA, confirming a scenario in which chromosomal rearrangements have been modeling karyotypes of different populations and settling in the absence of gene flow, a consequence of vicariant events that occurred in the different basins.

Effective practices for thermal tolerance polygon experiments using mottled catfish Corydoras paleatus

Temperature is an important environmental factor that affects how organisms allocate metabolic resources to physiological processes. Laboratory experiments that determine absolute thermal limits for representative species are important for understanding how fishes are affected by climate change. Critical Thermal Methodology (CTM) and Chronic Lethal Methodology (CLM) experiments were utilized to construct a complete thermal tolerance polygon for the South American fish species, Mottled catfish (Corydoras paleatus). Mottled catfish showed Chronic Lethal Maxima (CLMax) of 34.9 ± 0.52 °C and Chronic Lethal Minima (CLMin) of 3.8 ± 0.08 °C. Fish were chronically acclimated (∼2 weeks) to 6 temperatures ranging from 7.2 ± 0.05 °C →32.2 ± 0.16 °C (7 °C, 12 °C, 17 °C, 22 °C, 27 °C, and 32 °C), and CTM used to estimate upper and lower acute temperature tolerance. Linear regressions of Critical Thermal Maxima (CTMax) and Minima (CTMin) data with each acclimation temperature were used along with CLMax and CLMin to create a complete thermal tolerance polygon. The highest CTMax was 38.4 ± 0.60 °C for fish acclimated to 32.2 ± 0.16 °C, and the lowest CTMin was 3.36 ± 1.84 °C for fish acclimated to 7.2 ± 0.05 °C. Mottled catfish have a polygon measuring 785.7°C2, and the slope of the linear regressions showed the species gained 0.55 °C and 0.32 °C of upper and lower tolerance per degree of acclimation temperature, respectively. We compared slopes of CTMax or CTMin regression lines to each other using a set of comparisons between 3, 4, 5, or 6 acclimation temperatures. Our data demonstrated that 3 acclimation temperatures were as sufficient as 4 → 6 to pair with estimates of chronic upper and lower thermal limits for accurately determining a complete thermal tolerance polygon. Construction of this species' complete thermal tolerance polygon provides a template for other researchers. The following is sufficient to generate a complete thermal tolerance polygon: Three chronic acclimation temperatures that are spread somewhat evenly across a species’ thermal range, include an estimation of CLMax and CLMin, and are followed by CTMax and CTMin measurements.

Complete mitochondrial genome of four Scleromystax barbatus (Siluriformes: Callichthyidae) populations

Abstract The complete mitogenome of four Scleromystax barbatus populations distributed along the species natural range was reconstructed, comprising the first study with this genus and the second with Corydoradinae specimens sampled from their natural environment and deposited in permanent collections. The mitogenome of S. barbatus is a circular molecule of 16,694 base pairs (bp) comprising 37 genes, 22 of which are tRNA, two are rRNA, 13 are protein-coding genes and one control region (D-loop). An 18-nucleotide insertion sequence was found between the ATPase subunit 6 and COIII genes. Most genes are encoded on the heavy strand, while the ND6 and eight tRNAs are found on the light strand. Phylogenetic analyses using other available Callichthyidae mitogenomes confirmed the monophyly of Callichthyinae and Corydoradinae and indicate that S. barbatus populations form a separate and more closely related branch of Corydoras nattereri + Corydoras paleatus.

Reproduction performance of corydoras fish Corydoras paleatus spawned with different male to female ratio

The sex ratio in spawning can affect the efficiency and success of hatchery activities because sex ratio in spawning affects the number of eggs, the degree of fertilization, and the degree of hatching of eggs. Until now, there is limited research conducted in Corydoras paleatus fish spawning thus this study aims to determine differences in the reproductive performance of C. paleatus with different male sex ratios. This study uses three treatments, which are the ratio of fish male and female (1:1), (2:1), and (3:1). Each treatment uses one female fish. The vessel used in fish spawning is an aquarium with a size of 50 × 25 × 30 cm3. Spawning lasts for seven days and eggs are collected every day at 08.00. The number of eggs and larvae produced was not significantly different between treatments. Larvae produced by C. paleatus were 2,154 fish or 538 fish per female per week. The ratio (1:1) was considered an appropriate ratio in spawning C. paleatus fish because it has a high efficiency value.

Oxidative stress responses after exposure to triclosan sublethal concentrations: an integrated biomarker approach with a native (Corydoras paleatus) and a model fish species (Danio rerio)

ABSTRACT Triclosan (TCS) is a synthetic broad-spectrum antimicrobial agent commonly used world-wide in a range of personal care and sanitizing products detected frequently in aquatic ecosystems. The aim of this study was to examine biochemical markers responses triggered by TCS in Danio rerio and in a native South American fish species (Corydoras paleatus). Further, an integrated approach comparing both test fish species was undertaken. These fish organisms were exposed to 100 or 189 µg TCS/L for 48 h. The activities of catalase (CAT), glutathione-s-transferase (GST), superoxide dismutase (SOD), and lipid peroxidation levels (LPO) and total antioxidant capacity against peroxyl radicals (ACAP) were determined in liver, gills, and brain. Acetylcholinesterase activity (AChE) was measured in the brain. Multivariate analysis showed that the most sensitive hepatic parameters were activities of GST and SOD for C. paleatus while LPO levels were for D. rerio. In gills the same parameters were responsive for C. paleatus but CAT in D. rerio. ACAP and GST activity were responsive parameters in brain of both species. Integrated biomarker responses (IBR) index demonstrated similar trends in both species suggesting this parameter might serve as a useful tool for quantification of integrated responses induced by TCS.

Gill morphology and morphometry of the facultative air-breathing armoured catfish, Corydoras paleatus, in relation on aquatic respiration.

The Neotropical armoured catfish Corydoras paleatus is a facultative air-breathing teleost commonly exported as ornamental fish. In this species, air breathing enables it to survive and inhabit freshwater environments with low oxygen levels. Therefore, it is important to analyse the gills from a morphological aspect and its dimensions in relation to body mass with reference to aquatic respiration. For that, the gills were analysed using a stereoscopic microscope for morphometric studies, and structural and ultrastructural studies were carried out to compare the four branchial arches. Furthermore, two immunohistochemical techniques were used to locate and identify the presence of a Na+ /K+ pump. The characterization of the potential for cell proliferation of this organ was assessed using an anti-PCNA antibody. The results show that gills of C. paleatus present some characteristics related to its diet and lifestyle, such as the limited development of gill rakers and the abundance of taste buds. In addition, other special features associated with the environment and bimodal breathing were observed: scarce and absent mucous cells (MCs) in the gill filaments and branchial lamellae, respectively, and the localization of mitochondria-rich cells (MRCs) covering the basal third of the branchial lamellae, which reduces the gill respiratory area. A peculiar finding in the gill epithelium of this armoured catfish was the presence of mononuclear cells with sarcomeres similar to myoid cells, whose functional importance should be determined in future studies. Finally, in C. paleatus, the interlamellar space of gill filaments is an important site for cell turnover and ionoregulation; the latter function is also performed by the branchial lamellae.

Trophic ecology of the Neotropical tolerant fish Corydoras paleatus under the influence of contrasting environmental conditions in a prairie stream.

Worldwide, land use changes and urbanization affect habitat and biota in streams, drastically disrupting environmental conditions and biotic interactions. We evaluated the trophic ecology of the tolerant fish Corydoras paleatus in a prairie stream with contrasting environmental conditions intimately aligned with different nearby land uses. Gut analyses was conducted at three stream reaches with contrasting ecological attributes regarding water quality, habitat structure and riparian condition. A total of 231 guts were analyzed and 15 prey items identified. A significant variation in composition and structure of the dietary assemblage, niche breadth and feeding patterns of C. paleatus under different environmental conditions was observed. Psychodidae prevailed in most deteriorated environmental conditions and Chironomidae, followed by nematodes, in stream reaches where environmental conditions improved. Maximum niche breadth and a larger proportion of generalist individuals were found at the most deteriorated site. Conversely, the proportions of specialized individuals were slightly higher at sites with better ecological conditions. Psychodidae and mineral fragments were positively correlated with the most detrimental conditions, while filamentous algae prevailed where these conditions improved. Overall, good evidence suggesting that trophic ecology of a tolerant species is affected by local environmental conditions in water quality, habitat structure and riparian corridor was observed.

Two new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea: Gyrodactylidae) parasitizing introduced poeciliids in Patagonia.

Gyrodactylus superbus (Szidat, 1973) Popazoglo Boeger, 2000 was described from Corydoras paleatus (Jenyns) (Callichthyidae) and represents the only known viviparous gyrodactylid reported from the Parano-Platense basin of Argentina. We describe two new species of viviparous neotropical gyrodactylids parasitizing the introduced poeciliid, Cnesterodon decemmaculatus (Jenyns, 1842) (Poeciliidae), from southern Argentina: Gyrodactylus decemmaculati n. sp. and Gyrodactylus breviradix n. sp. The new species differ from other gyrodactylids parasitizing poeciliids in the morphology of superficial bars and hooklets. Gyrodactylus decemmaculati n. sp. has a superficial bar with two robust and rounded anterolateral projections (each with a ventral lobe), and a subtriangular shield, and has a slender hooklet with a delicate recurved point, a straight, elongate shaft, and a depressed, acute toe. Gyrodactylus breviradix n. sp. has a superficial bar with two robust, elongate anterolateral projections, folded inward, and a trapezoidal shield, and has a hooklet with a short point, angled at 90º, ending before level of toe tip, a straight, short shaft, a round, prominent heel, and a pointed, depressed toe. These identifications were supported by DNA analyses based on sequences of the ITS2 region and a barcoding gap analysis. Sequences of the Cytochrome oxidase II gene and fragments of the Internal Transcribed Spacers 1 for both species are also provided.

Helminth parasites of alien freshwater fishes in Patagonia (Argentina).

A survey of the helminth parasites of alien freshwater fishes from Argentinean Patagonia is presented, based on samples taken from 2010 to 2017 and including previous published records. A total of 1129 fishes were collected, belonging to 11 species from 7 families. We surveyed 34 localities in 12 river basins, and found 43 parasite taxa (15 digeneans, 14 monogeneans, 5 cestodes, 5 nematodes, and 4 acanthocephalans), belonging to 22 families. Data are presented as a parasite/host list with information on host species and localities, site of infection, parasite life–history stage, origin, previous records in Patagonia, and accession numbers to vouchers. The most frequently found helminths were monogeneans and digeneans. Our data suggest that invading fish in Patagonia have transmitted fewer parasite species than they have received by spillback. Twenty–three (53%) of the parasites seem to be acquired by the exotic fishes from native hosts, while 15 helminths were co–introduced along with their exotic fish host and continue to parasitize these alien fish but did not invade native hosts; 4 of these species were introduced with carp, 3 with Cheirodon interruptus, 3 with Corydoras paleatus, 3 with Cnesterodon decemmaculatus, 1 with Oncorhynchus tshawytscha, and 1 with Jenynsia multidentata. The majority of these co–introduced parasites came from the Brazilic ichthyogeographic region (10 species). This is the first review of helminth parasites of alien fishes in Argentina; in total 12 new records of parasites for Argentina, 6 new records of parasites for Patagonia, and 29 new host–parasite records are presented here. This list is far from complete, however, given that some basins in southern Patagonia remain unexplored in terms of parasite detection.

Trichodinids (Ciliophora) of Corydoras paleatus (Siluriformes) and Jenynsia multidentata (Cyprinodontiformes) from Argentina, with Description of Trichodina corydori n. sp. and Trichodina jenynsii n. sp.

During surveys of parasites of the pepper cory Corydoras paleatus Jenyns, 1842 and sided-livebearer Jenynsia multidentata Jenyns, 1842 from Samborombon River, Argentina, Trichodina corydori n. sp., Trichodina cribbi Dove and O’Donoghue, 2005 and T. jenynsii n. sp. were morphologically studied. Taxonomic and morphometric data for these trichodinids based on dry silver nitrate-impregnated specimens are presented. Trichodina corydori is characterized by a prominent blade apophysis, the section connecting the blade and central part is short, and the adoral ciliary spiral makes a turn of 370–380°. Trichodina jenynsii is characterized by curved blades and prominently-shaped denticle rays that are characteristically extremely long, tapering to thin sharp points in adult specimens. This study is the first formal report of these trichodinids from South America, and the description of two new species.

Histochemical differences along the intestine of Corydoras paleatus (Siluriformes: Callichthyidae).

The Neotropical catfish Corydoras paleatus is a facultative air-breather and the caudal half of the intestine is involved in gas exchange. In South America, air-breathing fishes are found in tropical or sub-tropical freshwaters where the probability of hypoxia is high. The aim of this study was to characterize by traditional histochemical and lectinhistochemical methods the pattern of carbohydrate in the intestinal mucosa. Intestine samples were taken from 25 healthy adult specimens collected in Buenos Aires (Argentina). Samples were fixed by immersion in 10 % buffered formalin and routinely processed and embedded in paraffin wax. Subsequently, these sections were incubated in the biotinylated lectins battery. Labeled Streptavidin-Biotin (LSAB) system was used for detection, diaminobenzidine as chromogen and haematoxylin as a contrast. To locate and distinguish glycoconjugates (GCs) of the globet cells, we used the following histochemical methods: PAS; PAS*S; KOH/ PA*S; PA/Bh/KOH/PAS; KOH/PA*/Bh/PAS; Alcian Blue and Toluidine Blue at different pHs. Microscopically, the general structure of vertebrate intestine was observed and showed all the cell types characteristic of the intestinal epithelium. The cranial sector of catfish intestine is a site of digestion and absorption and its structure is similar to other fish groups. In contrast, enterocytes of the caudal portion are low cuboidal cells; and between these, globet cells and capillaries are observed, these latter may reach the mucosal lumen. Underlying the epithelium, observed a well-developed lamina propria-submucosa made of connective tissue; this layer was highly vascularized and did not exhibit glands. According to histochemistry, the diverse GCs elaborated and secreted in the intestine are associated with specific functions in relation to their physiological significance, with special reference to their role in lubrication, buffering effect and prevention of proteolytic damage to the epithelium together with other biological processes, such as osmoregulation and ion exchange. The lectinhistochemical analysis of the intestinal mucosa reveals the presence of terminal residues of glucose, mannose and galactose. In conclusion, this study has shown that GCs synthesized in the intestine of C. paleatus exhibit a high level of histochemical complexity and that the lectin binding pattern of the intestinal mucosa is characteristic of each species and the variations are related with the multiple functions performed by the mucus in the digestive tract. The information generated here may be a relevant biological tool for comparing and analyzing the possible glycosidic changes in the intestinal mucus under different conditions, such as changes in diet or different pathological stages.

Phylogeography of Cnesterodon decemmaculatus (Cyprinodontiformes: poeciilidae) in Southern Pampas, Argentina: ancient versus recent patterns in freshwater fishes

The Southern Pampean Area includes the southernmost limit of the Brazilian subregion and represents an interesting model to study how evolution of the landscape has affected the distribution of freshwater fishes in time and space. The hydrogeographic pattern of the region results from a combination of factors including climatic and sea level changes occurred since the Miocene and extending into the Quaternary. The hydrologic basins of this region are isolated, and have a similar ichthyological composition among them. Here we use a phylogeographic approach to infer how paleoclimatic changes affected the distribution of genetic variation in the populations of freshwater fishes. We analyzed the control region of mtDNA of Cnesterodon decemmaculatus and compared it with published data for the species Jenynsia multidentata and Corydoras paleatus in the same area. Cnesterodon decemmaculatus showed two main haplotypes with scarce divergence and wide geographical distribution within the area. The low divergence found between the Cnesterodon decemmaculatus haplotypes and the results obtained in the demographic analyses could suggest that the presence of this species in the area have a recent demographic history. These results are in contrast with the pattern reported for Jenynsia multidentata and Corydoras paleatus, where data suggest an ancient history in the area. The incongruence in the observed phylogeographical patterns could be due to the different ecological requirements of each species, and to the various responses of them to the environmental conditions resulting from geologic and paleoclimatic changes occurred in the region during the Late Quaternary.

Immunohistochemical and ultrastructural evidence of functional organization along the Corydoras paleatus intestine.

The Neotropical catfish, Corydoras paleatus (Callichthyidae) is a facultative air-breathing teleost that makes use of the caudal portion of the intestine as an accessory air-breathing organ. This portion is highly modified, being well vascularized with capillaries between epithelial cells, which makes it well suited for gas exchange. Instead, the cranial portion is a digestion and absorption site, as it has a typical intestinal epithelium with columnar cells arranged in a single row, villi and less vascularized tunica mucosa. Therefore, the intestine was studied by light and electron microscopy to assess differences between the cranial, middle and caudal portions. To characterize the potential for cell proliferation of this organ, we used anti-proliferating cell nuclear antigen antibody and anti-Na(+) K(+) -ATPase monoclonal antibody to detect the presence of Na(+) /K(+) pump. In C. paleatus it was observed that cell dynamics showed a decreasing gradient of proliferation in cranio-caudal direction. Also, the intestine of this catfish is an important organ in ionoregulation: the basolateral Na(+) /K(+) pump may have an active role, transporting Na(+) out of the cell while helping to maintain the repose potential and to regulate cellular volume.

Revisionary study of the armored catfish Corydoras paleatus (Jenyns, 1842) (Siluriformes: Callichthyidae) over 180 years after its discovery by Darwin, with description of a new species

ABSTRACT The taxon known as Corydoras paleatus carries one of the most complex taxonomic histories among Corydoradinae catfishes. A comprehensive review of specimens attributed to that species from several localities was carried out, allowing the clear recognition of C. paleatus and also of a new species previously misidentified as C. paleatus , described herein. Corydoras paleatus can be distinguished from its congeners by presenting the following unique combination of features: perpendicularly directed serrations along entire posterior margin of the pectoral spine; three large black blotches along midline of flank; hyaline or black pectoral fin; and transversal black bars on caudal-fin lobes. Corydoras paleatus is known from the lower rio Paraná basin, coastal rivers from Southern Brazil and Uruguay and rio Uruguai basin. The new species can be distinguished from its congeners by having the following unique combination of features: three large black blotches along midline of flank; three nasal pores; mesethmoid short; infraorbital 2 not in contact with compound pterotic; striated black spots from the snout tip to nuchal plate region; markedly rounded snout; and anterior portion of dorsal fin spotted. The new species is known from the upper rio Uruguai basin, from the rivers Canoas, do Peixe and Pelotas.

Polyphasic growth in fish: a case study with Corydoras paleatus (Siluriformes, Callichthyidae)

ABSTRACT A weight-length relationship was established for Corydoras paleatus (Jenyns, 1842) (Siluriformes, Callichthyidae) (n=596) from samples taken in November-December 2009 and March-April 2010, in Pinguela Lagoon (29°46'57"S; 50°11'16"W), Rio Grande do Sul, Brazil. The species showed a polyphasic allometric growth pattern, each stanza described by an independent power equation controlled by a switch function: W = a1Lb1 ∙ (1 + eRsc ∙ (L-SCP))-1 + a2Lb2 ∙ [1 - (1 + eRsc ∙ (L-SCP))-1] ; where W is the expected weight for a specific length L, a1 and a2 are the proportionality coefficients for stanzas 1 and 2, b1 and b2 are the allometric coefficients for stanzas 1 and 2, Rsc is the stanza changing rate for the switch function and SCP is the stanza changing point for the switch function. The stanza changing point was estimated as 5.28 cm, corresponding with the length at first maturity for this species Lmat (5.29 cm). Our data suggest that a complex growth pattern can be in nature, and perhaps not often identified because trends are obscured by natural variability.

Ichthyofauna of the hydrographic basin of the Chasqueiro Stream (Mirim Lagoon system, southern Brazil): generating subsidies for conservation and management

Studies that organize lists of species are essential and act as the starting point for future discussions on the ecology of fish in environments that are poorly studied. The present paper describes the fish assemblage of the hydrographic basin of Chasqueiro Stream, an important component of the Mirim Lagoon system. Fish were collected during one year period between August/2012 and July/2013 in six sites, comprising three biotopes: upstream, reservoir and downstream. A total of 22,853 specimens were collected, and were distributed into 83 species, 20 families, and eight orders. The two species with the largest number of individuals captured were Bryconamericus iheringii with 2,904 (12.71%) and Cheirodon ibicuiensis with 2,868 (12.55%). Characiformes and Siluriformes were the most representative orders in terms of richness and abundance. Bryconamericus iheringi and Cyanocharax alburnus were the species with the highest abundance upstream, while Hyphessobrycon luetkenii and Corydoras paleatus contributed more to the abundance downstream. Cheirodon ibicuhiensis and Heterocheirodon jacuhiensis were the most representative species in the reservoir. This study revealed a rich fauna of fish, which should be preserved for future generations and for the maintenance of local and regional biodiversity.

Mercury bioaccumulation in fishes of a paddy field in Southern of Brazil

Aim: The aim of present study was to evaluate the Hg concentration in two species of fish (Astyanax sp and Corydoras paleatus) and its potential use as a biomonitor, in order to know if the use of pesticides and fertilizers in paddy can enhance the Hg contamination to adjacent aquatic environment.MethodsSoil, suspended particulate matter and fish samples were sampled in a paddy field in South Brazil. A cold vapor system, coupled with a GBC 932 atomic absorption spectrophotometer was used for total Hg determinations in samples.ResultsThe paddy soil shows Hg concentration 2-fold higher (mean 31 ng g-1) in comparison to background areas (not cultivated). Suspended particle matter Hg concentration in paddy channels (mean 232.5 ± 44.2 ng g–1) are 1.5 times higher than the regional background. The analyzed fish specimens Astyanax sp in paddy showed Hg concentration 4-fold higher and significant different to background area. The mean Hg concentration in fish was: 51.7 ± 19.5 ng g–1 in Astyanax sp and 156.8 ± 44.0 ng g–1 in Corydoras paleatus.ConclusionsConsidering the linear regression and Man whitney test hypothesis to Hg concentration in fish tissue from paddy suggests that Astyanax sp. can be a good biomonitor of Hg contamination, whereas Corydoras paleatus is a potential biomonitor. However, more studies with Corydoras are necessary in order to aggregate consistency to this hypothesis.

Insecticides biomarker responses on a freshwater fish Corydoras paleatus (Pisces: Callichthyidae)

This study was undertaken to investigate the effects of sublethal concentration of three different classes of insecticides (carbamate, organophosphate, and pyrethroid compounds) on the freshwater fish Corydoras paleatus. For this purpose, fish were exposed for 96 hours to commercial pesticides. Different biomarkers were analyzed as levels of lipid peroxidation (LPO), piscine micronucleus test, and enzymatic activities of catalase (CAT), glutathione S-transferase (GST), and acetylcholinesterase (AChE). The brain AChE was inhibited with carbaryl and methyl parathion, but no inhibition was observed with deltamethrin. The insecticides did not cause oxidative stress or genotoxic effects at the tested concentrations. Further studies are needed to elucidate the biotransformation of Corydoras paleatus insecticides and a possible resistance mechanism.

DNAbarcodingNeotropical fishes: recent advances from thePampaPlain,Argentina

The fish fauna of the Pampa Plain, the southernmost distribution range of many Neotropical species, was barcoded in this study. COI sequences were analysed by means of distance (K2P/NJ) and character-based (ML) models, as well as the Barcode Index Number (BIN). K2P/NJ analysis was able to discriminate among all previously identified species while also revealing the likely occurrence of two cryptic species that were further supported by BIN and ML analyses. On the other hand, both BIN and ML were not able to discriminate between two species of Rineloricaria. Despite the small genetic divergence between A. cf. pampa and A. eigenmanniorum, a tight array of haplotypes was observed for each species in both the distance and character-based methods. Deep intraspecific divergences were detected in Cnesterodon decemmaculatus (5%) and Salminus brasiliensis (6%). For Salminus brasiliensis, these findings were further supported by character-based (ML) evidence and meristic and morphological data. Our results also showed that Pampa Plain representatives of Salminus brasiliensis, Rhamdia quelen, Hoplias malabaricus, Synbranchus marmoratus, Australoheros facetus, Oligosarcus jenynsii and Corydoras paleatus differed by more than 3% from their conspecifics from other parts of South America. Overall, this study was able to highlight the likely occurrence of a cryptic species in Salminus brasiliensis and also illustrate the strong geographical structure in the COI sequence composition of seven fish species from South America.

Fish assemblage changes along a trophic gradient induced by agricultural activities (Santa Lucía, Uruguay)

The input of nutrients into rivers and other aquatic ecosystems is one of the most common causes of damage to the integrity of the ecosystem. The use of biological communities for water quality assessment is a common and effective practice. Among these biological indicators, the fish community is one of the most used in monitoring programs and ecosystems studies and so there is much knowledge about their response to the process of eutrophication. In this study we analyzed the fish composition, diversity and evenness in fourteen reaches, of low stream orders within a basin with differing land use intensity.The structure of the fish community was related with physiochemical water composition by canonical correspondence analysis, which enabled us to group the fish species according to their specific tolerance to eutrophication. Oligotrophic habitats were characterized by a higher evenness, larger individuals, a fish composition of at least 40% of sensitive species (Crenicichla scotti, Gymnogeophagus gymnogenis, Gymnogeophagus sp., Heptapterus mustelinus, Hoplias malabaricus and Rhineloricaria sp.) and less than 20% of very tolerant ones (Astyanax fasciatus, Cnesterodon decenmaculatus, Corydoras paleatus, Cyphocharax voga, Hisonotus sp., Pimelodella australis). Eutrophic reaches showed the opposite community features and a fish composition with more than 40% of very tolerant species and less than 20% of sensitive ones. Among the fourteen study reaches, four were classified as oligotrophic, six as mesotrophic and four as eutrophic.