Prochilodus lineatus (Val.) is one of the main target species of South American freshwater fisheries. The following null hypotheses regarding juvenile recruitment of P. lineatus were tested: (a) recruitment is not determined by variations in larval abundance and (b) recruitment is not determined by variations in discharge. For this purpose, variations in abundance of larvae in main channel drift and monthly captures of juveniles in a floodplain lake of the River Paraná were examined weekly between 2009 and 2016. Mean annual abundances of larval densities and CPUE of juveniles were correlated with a set of hydrometric variables. A positive correlation was found between the abundance of juveniles with high and persistent flood pulses. By contrast, larval abundance was not correlated with juvenile abundance. Pronounced contrast was found in the recruitment of P. lineatus between years of high and low discharge, which supports the hypothesis that floods are the main determining factor for recruitment of this species.
Summary
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.
SummaryLength-weight relationships (LWR) were estimated for 12 species, representing three orders and eight families of fishes from the Paran a and Uruguay rivers in Argentina: Acestrorhynchus pantaneiro, Cynopotamus argenteus, Pachyurus bonariensis, Pterodoras granulosus, Hypostomus commersoni, Pseudoplatystoma corruscans, Pimelodus maculatus, Parapimelodus valenciennis, Salminus brasiliensis, Prochilodus lineatus, Hoplias malabaricus and Leporinus obtusidens. For the last four species, the length at first spawning (L m ) was estimated using three different methods. The captures were made in shallow river areas during 2005-2013. Significant lengthweight relationships were found for all species. None or few LWRs were previously available for these species.
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