No abstract

The marine silverside (Odontesthes argentinensis) is an euryhaline species, distributed along the southwest coast of the Atlantic Ocean, present in estuaries, brackish coastal lagoons and shallow marine waters. It is a significant economic resource for local fisheries in southern Brazil, Uruguay and Argentina. The aim of this work was to contribute to knowledge on the stock spatial structure of the silverside, using otolith shape analysis, based on samples from nine locations in the Argentinian Sea, covering a large distribution range of the species. A combination of elliptic Fourier descriptors, Wavelet coefficients and otolith Shape indices were explored by multivariate statistical methods. The application of wavelet and combined wavelet, Fourier and Shape Indices were the most effective variables to discriminate between sampling sites (7.42 total error). PERMANOVA analysis of otolith shape revealed multivariate significant differences between north versus south locations (p < 0.0001). The results obtained show that the spatial structure of O. argentinensis presents a North–South gradient with marked differences between the extreme localities of the north (Mar del Plata, Quequén) with more elliptical shapes than those in the south (San Blas, San Antonio Este) and an isolated group conformed by Puerto Lobos.

The drainage of the Negro River is the most important watercourse in the Patagonia ecoregion and, together with the Colorado river basin, define an ecotone, i.e., a zoogeographic transition, where coexist the Brazilian and Patagonian lineages of freshwater fishes. The Patagonia ecoregion has 29 fish species, 15 native and the remaining introduced. For this study, the ichthyofauna of seven locations in the lower course of the Negro river drainage were sampled along two years. Gillnets, coastal trawls, cast nets, river trammel nets and fishing rods were used to catch specimens. A total of 13 species belonging to nine orders and 11 families were collected. The families Atherinopsidae and Characidae show the highest species richness and one exotic species, Cyprinus carpio Linnaeus, 1758, was recorded. The origin and distribution of some species is discussed, considering the role of human action and certain environmental factors.