Les caractéristiques morphologiques et biologiques de la population actuelle d'Alose feinte du Rhône (Alosa fallax rhodanensis) sont présentées. Elles sont analysées à partir d'un lot de 1479 adultes capturés (pêche au filet) lors de leur migration anadrome au cours de trois années.Les critères morphologiques utilisés (notamment le nombre de branchiospines) et leur faible variabilité individuelle ne font apparaître qu'un seul taxon, identifié comme étant celui d'Alosa fallax rhodanensis.La longueur moyenne (Lf) est de 433 mm pour un poids moyen de 1115 g, avec un spectre d'âge s'étalant de 3 à 8 ans. Le rapport des sexes est en moyenne en faveur des femelles (mâles/femelles = 0,61). Celles-ci ont un âge moyen de remontée (AMR) plus élevé (5,24 ans) que celui des mâles (4,21 ans). A âge égal, les femelles montrent une plus forte croissance linéaire et pondérale que les mâles.L'âge moyen de première reproduction (AMPR) est plus faible que l'AMR et montre un phénomène d'itéroparité important ; il est plus élevé chez les femelles (4,00 ans) que chez les mâles (3,35 ans). Le nombre de reproductions antérieures varie de 1 à 5 et le pourcentage de poissons s'étant déjà reproduits au moins une fois est en moyenne de 48,6 %, mais est plus élevé chez les femelles.Il existe des différences inter-annuelles significatives pour la plupart des paramètres biologiques.Les résultats obtenus sont discutés et comparés à ceux de DOUCHEMENT (1981) Used morphological characters (mainly the number of gillrakers) and their low individual variability reveal that only one taxon is present in the sample and is identified as Alosa fallax rhodanensis.Mean length (Lf) and weight are 433 mm and 1115 g, respectively. Age is ranged from 3 to 8 years and sex-ratio is on average in favour of females (males/females = 0.61). Females are older than males (5.24 years against 4.21 years for mean migration age (AMR) and get a better growth in size and weight at the same age.Mean first reproduction age (AMPR) is lower than AMR because of a large iteroparity phenomenon. AMPR is higher in females (4.00 years) than in males (3.35 years). Number of previous spawnings is ranged from 1 to 5 and mean proportion of previous spawners (at least one time) is 48.6 %, but it is higher in females.There exist significant interannual differences in the most biological parameters.Present results are discussed and compared to these obtained by DOUCHEMENT (1981) by taking into account variability related to sampling methods. On one hand, they confirm some biological characteristics of Alosa genus and studied taxon. On the other hand, they suggest a possible change in demographical strategy of Rhone Shad population in 20 years.
The Itaipu Hydroelectric Power Plant is the second largest in the world in power generation. The artificial barrier created by its dam imposes an obstacle for fish migration. Thus, in 2002, a fish pass system, named Piracema Channel, was built to allow fish to access areas upstream of the reservoir. We tested the potential of metabarcoding to monitor the impact of both the dam and associated fish pass system in the Parana River fish communities and to compare it with traditional monitoring methods. Using a fragment of the 12S gene, we characterized richness and community composition based on amplicon sequence variants, operational taxonomic units, and zero-radius OTUs. We combined GenBank and in-house data for taxonomic assignment. We found that different bioinformatics approaches showed similar results. Also, we found a decrease in fish diversity from 2019 to 2020 probably due to the recent extreme drought experienced in southeastern Brazil. The highest alpha diversity was recorded in the mouth of the fish pass system, located in a protected valley with the highest environmental heterogeneity. Despite the clear indication that the reference databases need to be continuously improved, our results demonstrate the analytical efficiency of the metabarcoding to monitor fish species.
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