Chromosomes of three freshwater stingrays (Rajiformes Potamotrygonidae) from the Rio Negro basin, Amazon, Brazil

Potamotrygonidae is the representative family of South American freshwater elasmobranchs. It is a monophyletic group containing 20 species grouped into three genera. Three species belonging to two genera of this family were collected from the middle Negro River, Amazonas, Brazil, and studied cytogenetically: Paratrygon aiereba, Potamotrygon motoro and Potamotrygon orbignyi. Paratrygon aiereba presented 2n = 90 chromosomes and 4M+2SM+10ST+74A. Both species of Potamotrygon presented 2n = 66 chromosomes and differed in their chromosomal formulas: P. motoro had 18M+12SM+10ST+26A and P. orbignyi had 22M+10SM+8ST+26A. No sex heteromorphism was detected. The Fundamental Number (FN) was 106 for the three species. A system of multiple NORs was found in the three species, but with interspecific differences in terms of location and position of the active Ag-NORs sites. Paratrygon aiereba presented only four sites on the short arms of two chromosomal pairs, both in terminal regions. Potamotrygon motoro presented seven sites, on the long and short arms, all in terminal regions of non-homologous chromosomes; P. orbignyi presented eight sites on the long arms, all in terminal regions, of non-homologous chromosomes. The constitutive heterochromatin was in pericentromeric regions of all chromosomes, and no significant interspecific difference was found in relation to this marker.     

Carbon dioxide and methane emissions from interfluvial wetlands in the upper Negro River basin, Brazil

Extensive interfluvial wetlands occur in the upper Negro River basin (Brazil) and contain a mosaic of vegetation dominated by emergent grasses and sedges with patches of shrubs and palms. To characterize the release of carbon dioxide and methane from these habitats, diffusive and ebullitive emissions and transport through plant aerenchyma were measured monthly during 2005 in permanently and seasonally flooded areas. CO₂ emissions averaged 2193 mg C m^?2 day^?1. Methane was consumed in unflooded environments and emitted in flooded environments with average values of ?4.8 and 60 mg C m^?2 day^?1, respectively. Bubbles were emitted primarily during falling water periods when hydrostatic pressure at the sediment?Cwater interface declined. CO₂ and CH₄ emissions increased when dissolved O₂ decreased and vegetation was more abundant. Total area and seasonally varying flooded areas for two wetlands, located north and south of the Negro River, were determined through analysis of synthetic aperture radar and optical remotely sensed data. The combined areas of these two wetlands (3000 km²) emitted 1147 Gg C year^?1 as CO₂ and 31 Gg C year^?1 as CH₄. If these rates are extrapolated to the area occupied by hydromorphic soils in the upper Negro basin, 63 Tg C year^?1 of CO₂ and 1.7 Tg C year^?1 as CH₄ are estimated as the regional evasion to the atmosphere.     

A new Apistogramma species (Teleostei, Cichlidae) from the Rio Negro in Brazil and Venezuela

Apistogramma diplotaenia sp.n. occurs in the upper and middle Rio Negro. The largest among 186 specimens studied is a 29.2 mm SL male, the largest female is 22.9 mm SL. Distinguishing characters include a unique colour pattern, consisting of two dark bands along the side which converge anteriorly and posteriorly. A comparative osteological study, including other species of Apistogramma and the genera Taeniacara and Apistogrammoides , indicates a progressive forwards loss of infraorbital ossicles and foramina among dwarf cichlids. The long, rod-like interarcual cartilage of Apistogramma, Apistogrammoides and Satanoperca possibly represents a plesiomorphic condition otherwise unknown among cichlids.     

Two new species of Pseudancistrus (Siluriformes,Loricariidae) from the Amazon basin,northern Brazil

Two new species of Pseudancistrus, a genus diagnosed by non-evertible cheek plates and hypertrophied odontodes along the snout margin, are described from two drainages of the Brazilian Shield: Pseudancistrus kayabi from the rio Teles Pires (rio Tapajós basin) and Pseudancistrus asurini from the rio Xingu. The new species are distinguished from congeners (Pseudancistrus barbatus, Pseudancistrus corantijniensis, Pseudancistrus depressus, Pseudancistrus nigrescens, Pseudancistrus reus, and Pseudancistrus zawadzkii) by the coloration pattern. Pseudancistrus kayabi has dark bars on the dorsal and caudal fins which are similar to that of Pseudancistrus reus from the Caroní River, Venezuela. Pseudancistrus asurini is unique among Pseudancistrus in having whitish tips of the dorsal and caudal fins in juveniles to medium-sized adults.     

Autotrophic energy sources for Paracheirodon axelrodi (Osteichthyes, Characidae) in the middle Negro River, Central Amazon, Brazil

The cardinal tetra (Paracheirodon axelrodi) is the most abundant species of the Brazilian ornamental fish trade, constituting more than 80% of the ornamental fish collected in the middle Negro River basin. Stable isotope analyses were used to identify the autotrophic carbon sources and trophic position for the cardinal in relation to the plant groups at the base of its foodchain. Filamentous algae, tree and plant leaves and cardinals were collected in stream habitats, flooded forest and interfluvial swamps (campos) during peak flood, falling water and low water periods. δ¹⁵N values of the cardinal in relation to the plants at the base of the food chain indicated a trophic position of omnivore. Values of δ¹³C for the plants ranged from −43.1 to −26.4‰, with averages of −37.6, −30.4, and −29.4‰ for filamentous algae, flooded forest leaves, and campo leaves, respectively. The δ¹³C values for the cardinal ranged from −35.0 to −27.9‰, with an average of −31.4‰. Relative contributions of plants to fish carbon were estimated in a two end-member mixing model which determined that the leaves (flooded forest and campo leaves combined) and filamentous algae had average relative contributions to cardinal carbon of 71% and 29%, respectively. However, seasonal variation in the relative contributions was encountered throughout the hydrological cycle. The cardinals least enriched in ¹³C were encountered in November during the falling water period, indicating that they had perhaps recently migrated down from interfluvial campos where filamentous algae production is significant. Considering that algal production has been reported to be less than 1% of total primary production in the Negro River, these results could suggest some evidence of selective herbivory in the cardinal’s food chain. Handling editor: J. M. Melack     

Pollen sources used by species of Meliponini (Hymenoptera: Apidae) along the Rio Negro channel in Amazonas,Brazil

This work analyses the pollen stored by Meliponini bees whose nests were sampled along the Rio Negro channel, Amazonas, Brazil, during the final phase of the rainy season, which is also the time of pollen scarcity. From a total of 51 samples studied, 78 pollen types were identified, of which 39 were determined to species level. The pollen types were from 70 genera and 42 families. Based on the pollen records, a clustering analysis was performed, as well as the calculation of the trophic overlap index. The study demonstrates that the plants used by the bees do not depend on them for pollination in most cases; it rather suggests scarcity of pollen resources from the plants adapted to the pollination of Meliponini, and emphasises the ability of such bees to switch to new available resources. This work indicates a list of important plants for meliponiculture suitable for cultures near meliponaries.     

Group sizes and compositions of monkeys in the upper Amazon basin

Eleven species of New World monkeys inhabit the basin of the upper Amazon. Twice, for a total 16 months, the author studied the group sizes and compositions of these species in the basin of the Rivers Caquetá and Putumayo, particularly in the two study areas established in the basin of the River Peneya, a tributary of the River Caquetá. Data obtained by the author were compared with those on the same and close relative species living in other places. And the author could conclude that each species, showing a considerable range of variation in group size and composition, has a common specificity for the social structure of the unit group.     

Fish mercury bioaccumulation as a function of feeding behavior and hydrological cycles of the Rio Negro, Amazon

The acidic black waters of the Rio Negro are unimpacted by anthropogenic sources and yet, are characterized by fish containing relatively high Hg concentrations. Regular annual flooding alters the aquatic environment, thereby affecting fish feeding strategies. We studied the impact of annual flooding on fish-Hg bioaccumulation. Tucunarés (Cychla spp, carnivorous), Peixe-cachorro (Hydrolycus scomberoides, carnivorous), Traíra (Hoplias malabaricus, carnivorous), Piranha-branca (Serrasalmus aff. eigenamanni, carnivorous), Piranha-preta (Serrasalmus rhombeus, carnivorous), Acará (Acarichthys heckellii, omnivorous), Aracú (Leporinus friderici, omnivorous), Orana-preta (Hemiodus unimaculatus, omnivorous), Sardinha (Triportheus elongatus, omnivorous), Branquinha (Potamorhina latior, detritivorous), Jaraqui-escama-fina (Semaprochilodus taeniurus, detritivorous), and Pacú-branco (Myleus torquatus, herbivorous) were studied during high (July) and low waters (February) and categorized by body mass. Regardless of hydrological period, ranges of total-Hg concentrations were higher for carnivorous than for omnivorous, detritivorous and herbivorous species. Some species (Traíra, Sardinha, Peixe-cachorro, Piranha branca, Piranha preta) showed changes in feeding patterns as indicated by an inverse trend of Hg bioaccumulation with season. Species with similar trends of Hg bioaccumulation showed higher Hg concentrations during the flooded season (Aracú, Pacú branco and Orana preta) and some had lower Hg (Acará, Branquinha and Tucunarés). Fish Hg concentration is species specific and reflects changes in feeding-behavior dominance brought by annual inundation.     

Description of a new Acaronia species (Teleostei, Cichlidae) from the Rio Orinoco and Rio Negro drainages

Acaronia vultuosa sp.n. occurs in the Rio Orinoco and upper Rio Negro drainages. In the Rio Negro it overlaps slightly the range of its only congener, A. nassa (Heckel), from which it can be distinguished by (1) the lack of microbranchiospines on the first gill arch, (2) thc separate instead of coalesced anterior gill rakers on the first gill arch, and (3) the colour pattern, which includes a much larger midlateral blotch and a different pattern of dark markings on the head.     

Anthropogenic impact of mercury accumulation in fish from the Rio Madeira and Rio Negro rivers (Amazonia)

Fish is an important concentrator of mono-methyl mercury and the main route to human contamination. We compared fish Hg bioaccumulation (within similar weight ranges) in two Amazonian river habitats during high-water seasons. The Rio Madeira has been greatly impacted by agriculture, alluvial gold extraction, and a hydroelectric reservoir, whereas the Rio Negro is much less affected by these human activities. The species at the top of the food web, Hoplias malabaricus (piscivorous; 80-668 ng Hg/g) and Cichla spp. (piscivorous; 42–747 ng Hg/g) showed the highest range of Hg concentrations. Nonpiscivorous species with comparable weight range, such as Potamorhina latior (detritivorous; 20–157 ng Hg/g) and Myleus torquatus (herbivorous; 2–182 ng Hg/g), had lower Hg concentrations. Triportheus elongatus (omnivorous; 5–350 ng Hg/g), with the lowest weight range, also showed a low range of Hg concentrations. Despite the Rio Madeira's higher sediment load as well as environmental impacts (deforestation, agriculture, hydroelectric reservoir, and alluvial gold mining) on natural Hg release, fish Hg bioaccumulation was no different between the two river habitats for nonpiscivorous species. In this small observational study only the species at the top of the food web (M. torquatus, Cichla spp, T. elongatus) showed higher mean Hg concentrations in the Rio Madeira than the dominantly wilderness habitat of the Rio Negro.     

Stress responses of the endemic freshwater cururu stingray (Potamotrygon cf. histrix) during transportation in the Amazon region of the Rio Negro

Potamotrygon cf. histrix (cururu stingray) are endemic freshwater stingrays from the middle region of the Rio Negro in the Brazilian Amazon basin and are exported worldwide as ornamentals caught by artisanal fishermen. The transport process from capture to final destination is long and stressful. This study quantified stress related changes in corticosterone, blood and water samples (baseline, pre-transport, 3h, 12h and 24h) analyzed during a transport experiment which tested two water additives (tetracycline and the probiotic Efinol). There was a significant stepwise increase in corticosterone levels in stingrays over transport time in combination with osmoregulatory disturbances suggesting a stress related role of this corticosteroid. There were significant increases in water conductivity, Na(+) and K(+) losses and ammonia excretion. Blood parameters such as glucose, hematocrit, red blood count and urea did not change significantly during the experiment. Glucose levels did not increase significantly during transport and this may be due to the fact that other elasmobranchs have been shown to rely more on ketone bodies for energy rather than glucose and produce ammonia as their main nitrogenous waste. The mineralocorticoid action of this hormone has been shown in elasmobranchs and most likely plays a role in osmotic homeostasis. The use of probiotic and especially antibiotic should be avoided since no beneficial effects were observed.     

Historical processes explain fish diversity in the upper Amazon River basin

Hydrobiologia - Despite decades of investigation, there are few ecological studies on the Amazonian fish fauna that have looked both at the main factors shaping the fish assemblages at a regional...     

Two remarkable new trichomycterid catfishes from the Amazon basin in Brazil and Colombia

Two Amazonian freshwater trichomycterid catfishes, Sarcoglanis simplex and Malacoglanis gelatinosus , are described as new genera andspecies and placed in a new subfamily Sarcoglanidinae. The relationships of this new subfamily and those of the Trichomycterinae, Nematogenyinae, Phreatobiinae and Glanapteryginae are discussed.     

Biological quality of waters from an impacted tropical watershed (middle Rio Doce basin,southeast Brazil), using benthic macroinvertebrate communities as an indicator

Taking the watershed as the unit for intervention and conservation, in this study we assess water quality along a stretch of impacted watershed of considerable economic importance, the middle Rio Doce basin, using the benthic macroinvertebrate community, along with physical and chemical characteristics as parameters, for the classification of 20 sampling stations. The results showed that parameters often used in temperate regions are also useful to assess water quality in tropical ecosystems, where no specific methodology has yet been developed. In spite of a clear distinction between stations of good and bad quality, the multimetric biological analysis alone was not sensitive enough to identify intermediate conditions. Grouping similar and dissimilar stations by Cluster analysis of physical and chemical variables and biological data, however, it was possible to distinguish three categories based on the biological quality of the water: (1) stations with poor quality water; (2) stations with high quality water, and (3) stations with water of intermediate quality. Classifications of water quality of this sort will hopefully assist decision-makers in defining restoration/conservation strategies, and will provide an important tool for monitoring biodiversity and water quality in tropical watersheds.     

Two new species of spotted Hypancistrus from the Rio Negro drainage (Loricariidae,Hypostominae)

Two new species, Hypancistrus phantasma and Hypancistrus margaritatus, are described based on material from the Rio Negro drainage. Both species are distinguished from congeners by unique color patterns. Hypancistrus phantasma is described from the Rio Uaupes and differs from congeners by having a tan body with small dark spots (vs. dark with light spots or with saddles or stripes). Hypancistrus margaritatus is described from the Takutu River and differs from congeners by having densely-packed light spots on a dark brown background, with spots about the size of the nasal aperture (vs. sparse light spots either smaller or larger than the nasal aperture, or brown to black spots, saddles, or stripes).     

Diel variations of phytoplankton and bacterioplankton production rates in four tropical lakes in the middle Rio Doce basin (southeastern Brazil)

Studies on phytoplankton production conducted in lakes of the middle Rio Doce basin demonstrated significant diurnal and seasonal variations with high phytoplankton production rates recorded in the morning hours during the dry periods. Bacterial production data for these lakes had not been recorded until now. The present study had as working hypothesis that bacterial production may contribute significantly to carbon fixation, particularly in lakes rich in organic matter and that this production varies diurnal and seasonally thus altering BP/PP ratios. In order to test this hypothesis the study had as objective to estimate phytoplankton and bacterioplankton production rates along with the concentrations of carbon, nitrogen, and phosphorus in two periods of the day (morning and afternoon) and in two seasons (dry and rainy), in four lakes, being two lakes within the Rio Doce State Park and two at its surroundings. Among the selected lakes, Lake Amarela showed the highest nutrient concentrations and highest bacterial production. The results allow to conclude that despite exhibiting lower values when compared with the ones recorded for phytoplankton production, bacterioplankton production is essential to the general metabolism of the lakes, particularly for those rich in organic matter and exhibiting oligo-mesotrophic conditions.