Buenos Aires, Argentina
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Lucifora L.O.,National University of Misiones | Barbini S.A.,University of Buenos Aires | Vegh S.L.,Direccion de Pesca Continental | Scarabotti P.A.,National University of Santa | And 4 more authors.
Marine and Freshwater Research | Year: 2016

Freshwater elasmobranchs are threatened but little is known about them. Potamotrygon brachyura is the world's largest obligate freshwater elasmobranch. This makes it popular among fishermen and suggests a susceptibility to anthropogenic threats. We collected records of P. brachyura (n≤70) from media, fishermen and scientific sampling, to estimate its global geographic distribution (using both generalised additive and MaxLike models). Then, we estimated the species' exposure to habitat modification and fishing pressure, by applying multinomial ordinal models with threat levels as response and the presence or absence of P. brachyura as an independent variable. Distance to coast, depth, water temperature range, salinity range and mean water temperature were the main determinants of the distribution in the Río de la Plata. This resulted in a narrow coastal distribution. In the Uruguay and Paraná River basins, the probability of occurrence was positively associated with flow accumulation, percentage of open water and submerged vegetation, and lowland ecoregions, and negatively to wetness index and altitude. This limited the distribution to large lowland rivers. Approximately 41% of the range of P. brachyura in the Río de la Plata was subject to high habitat modification. In the Uruguay and Paraná River basins, this percentage reached 7%; however, the overlap with high fishing pressure was 59%. For conservation purposes, P. brachyura may function as an umbrella species. © CSIRO 2016.

Lattuca M.E.,CONICET | Lattuca M.E.,Grande Rio University | Lozano I.E.,Direccion de Pesca Continental | Brown D.R.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero Inidep | And 2 more authors.
Estuarine, Coastal and Shelf Science | Year: 2015

Age and growth, otolith shape and diet of Odontesthes nigricans were analysed in order to provide an insight into the life history of the species and furthermore, to assess their possible use as a tool for discriminating silverside populations from the South Atlantic Ocean (Punta María) and Beagle Channel waters (Varela Bay). The age and growth analysis was performed by counting daily increments and annual marks in sagittae otoliths. Length-at-age data of individuals <65 mm standard length (SL) were fitted to the Laird-Gompertz model (SLt = 6.22 exp 2.45 [1-exp (-0.02 t)]), which provided an excellent description of the pattern of daily growth for O. nigricans juveniles from Varela Bay. The spawning period was also assessed through back-calculation of hatching dates and it extended from November to February. The count of annual marks in larger individuals identified 7 year classes (0+ to 6+) in Varela Bay and 6 year classes (0+ to 5+) in Punta María. The von Bertalanffy growth model explained more than 95% of the growth patterns observed in O. nigricans from Varela Bay (SLt = 245.49 [1 - exp -0.24(t +0.46)]) and Punta María (SLt = 345.09 [1 - exp -0.15(t +0.31)]). Particularly, k and SL∞ varied significantly between sampling sites; reaching Punta María a larger SL∞ value with a lower k. Otolith shape variation was also explored using elliptical Fourier analysis and it showed significant differences between Varela Bay and Punta María populations. Furthermore, gut content analysis characterized O. nigricans as an invertebrate predator, being benthic organisms the most important components of its diet, which also showed significant site dependence. The use of all these analyses contributed to a holistic approach which maximized the likelihood of correctly identifying both O. nigricans populations in the southernmost limit of the species distribution. © 2015 Elsevier Ltd.

Gomez M.I.,Direccion de Pesca Continental | Sanchez S.,Northeast National University | Fuentes C.M.,Direccion de Pesca Continental
Journal of Applied Ichthyology | Year: 2014

The effects of preservation in 95% ethyl-alcohol and 5% formalin were analysed for 3 months on standard length of Prochilodus lineatus larvae from hatching to the end of the flexion process. Unyolked stages were raised under two feeding regimes: unfed and daily fed. All developmental stages that were preserved in formalin as well as the yolked and flexion-postflexion larvae stored in alcohol shrank significantly (2-6%). In contrast, unyolked preflexion larvae showed a slight but significant enlargement after storage in alcohol (1%). Shrinkage of preflexion stages was 2.5% higher when stored in formalin, while both preservative agents caused similar shrinkage in flexion-postflexion larvae (ca. 3%). Shrinkage levels after storage in alcohol were dependent on live length, decreasing or increasing with increasing length in yolked and flexion-postflexion larvae, respectively. The feeding regime did not affect length changes after preservation in either preservative agent. © 2013 Blackwell Verlag GmbH.

Avigliano E.,University of Buenos Aires | Avigliano E.,CONICET | Fortunato R.C.,University of Buenos Aires | Biole F.,University of Buenos Aires | And 4 more authors.
Neotropical Ichthyology | Year: 2016

The streaked prochilod Prochilodus lineatus (Valenciennes) is a commercially freshwater species from South America, distributed in the Plata basin. In the present work the morphometry (circularity, rectangularity, form factor, OL/OW and ellipticity indices) and chemistry (Sr:Ca, Ba:Ca, Zn:Ca) of lapilli otolith, and geometric morphometry of scales of streaked prochilod juveniles, in two sites in the Plata basin (Uruguay River and Estrella Wetland), were compared to determine if they are area-specific and to identify possible breeding areas. Otolith Ba:Ca ratios was 0.017±0.003 mmol/mol for Uruguay River while for Estrella Wetland individuals was bellow the detection limits. Zn:Ca ratios tended to be higher for the latter (0.03±0.002 mmol/mol). Significantly high circularity and low rectangularity values were obtained for Estrella Wetland otoliths (p < 0.05), while no significant differences for form factor, OL/OW and ellipticity were observed between sampling sites. Considering all scale geometric morphometry variables, discriminant analysis showed a good percentage of classification of individuals (90.5% for Estrella Wetland and 85.7 % for Uruguay River). These results indicate that the otolith microchemisty and morphometry (circularity and rectangularity indices) and scale morphometry are good markers of habitat and represent a potential tool for identification of streaked prochilod nursery areas. © 2016, Sociedade Brasileira de Ictiologia. All rights reserved.

Lozano I.E.,Direccion de Pesca Continental | Llamazares Vegh S.,Direccion de Pesca Continental | Domanico A.A.,CONICET | Espinach Ros A.,Direccion de Pesca Continental
Journal of Applied Ichthyology | Year: 2014

The aim of this work was to compare age determinations and precision using two deposition structures of trahira Hoplias malabaricus (Bloch, 1794): the scales, which are most frequently used, and otoliths (lapilli). The length-age relationships were obtained with both structures and compared with results from previous studies. The 163 sets of trahira otoliths (lapilli) and scales were 17-46 cm standard length (SL) from Cayastá (Santa Fe) and Islas Lechiguanas (Entre Ríos), Paraná River, Argentina. Three independent readings of each structure were conducted. An age bias plot was performed to compare age estimations from scales and otoliths. To assess the precision of age determinations using both structures, the percent agreement among readers for both structures and the coefficient of variation were calculated (%CV). The age-length relationships were plotted and fitted with the von Bertalanffy growth function for both structures and compared with previous works. Age readings recorded for scales were lower than those recorded for otoliths for ages above or equal to 3 years. Percent agreement among readers was higher than 80% for otoliths and less than 65% for scales. The%CV obtained for scales was 20% for young fish and 17% for adults. For otoliths the %CV was 7% for young fish and 3% for adults. The %CV obtained for scales was over the recommended limit (>7.6%). The von Bertalanffy parameters for scales were Linf  = 45.80 mm; k = 0.29; t0 = -1.34 and for otoliths were Linf = 40.76 mm; k = 0.39; t0 = -1.05. Precision of age estimations assessed from the percent agreement and the coefficient of variation indicates that the scales of the trahira are inappropriate to estimate age in population studies for juvenile and adult specimens. © 2013 Blackwell Verlag GmbH.

Fuentes C.M.,Direccion de Pesca Continental | Gomez M.I.,Direccion de Pesca Continental | Brown D.R.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero Caba Argentina | Arcelus A.,Comision Administradora del Rio Uruguay CARU Paysandu Uruguay | Espinach Ros A.,Direccion de Pesca Continental
River Research and Applications | Year: 2016

We evaluated the passage of early-stage fishes through the Salto Grande Dam using high-frequency downstream ichthyoplankton monitoring and five surveys involving samples taken upstream and downstream of the dam. Eggs and larvae of migratory fishes were captured downstream of the dam, usually during high discharges. Upstream and downstream larvae were frequently unyolked, which corresponds to individuals aged 4+ days, and represents a time significantly longer than that required for the displacement of the water mass from the dam to the sampling location. In low flow rate surveys, fish larvae of the same species and degree of development were captured immediately upstream and at 1, 10, 24 and 40km downstream of the dam. The densities and percentage of Pimelodinae larvae captured alive by short time and low speed tows were similar upstream and downstream of the dam, indicating that larval mortality was a result of sampling and not to the passage through the turbines. The results show that the larvae of fish that spawn in the middle section are partly transported to the lower section, and suggest that both spillway and turbine discharge should be considered part of the passage. We also found evidence that the passage of small and fragile Pimelodinae larvae through the Salto Grande Kaplan turbines does not significantly affect survival rates. © 2016 John Wiley & Sons, Ltd.

Fuentes C.M.,Direccion de Pesca Continental | Quiroga F.,Direccion de Pesca Continental
Journal of Plankton Research | Year: 2012

This study investigated to what extent natural predation or net feeding contribute to the presence of pre-flexion fish larvae in the stomachs of more developed larvae in ichthyoplankton samples from the Paraná River. A digestion trial and two sampling experiments were conducted. First, pre-flexion larvae were offered to post-flexion larvae and prey digestion stages were analyzed hourly. Second, we evaluated the number of prey retained in the mouth and contained in the stomachs of predators from 1, 5 and 10 min samples taken with a single-standard plankton net (300-μm mesh size) and with two standard and 1600-μm mesh size nets simultaneously deployed. At time zero, most of the prey were in a fresh condition. Digested prey accounted for ∼40 of the prey after 1 h and were dominant after 6 h digestion. Stomachs of predators captured with the standard net contained significantly more fresh and bitten prey in longer- than in short-duration samples, whereas no prey were observed in samples collected with the larger mesh size net. Our results show intra-net predation in the 300-μm mesh net and imply that most prey were eaten in the net. © 2012 The Author.

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