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Caucete, Argentina

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

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. Source

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

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. Source

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

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. Source

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

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. Source

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