Freshwater fishes of the Río de la Plata: current assemblage structure

Abstract

Few studies have addressed the composition of fish assemblages of the freshwater Río de la Plata (RdlP) and have only been limited to species lists gathered over the last two centuries. As such inventories have never been reviewed or validated by fish sampling, the richness and structure of RdlP fish assemblage are poorly known. Hence, we conducted an exhaustive literature review and a fieldwork in six coastal points of Argentina to update the species composition and determine the hierarchical structure of the fish assemblage. From the 206 species registered in the literature, 48 were not confirmed, 13 were absent, five were taken as synonymized species, 29 were supported by literature and 107 were confirmed; one was an established exotic species, and three were a non-established exotic species. The findings reported here suggest that the fish assemblage currently comprises 141 species, including four new records. Analysis of fieldwork data in number and weight of fish captured resulted in an assemblage hierarchical structure of five dominant, 22 frequent, and 45 rare species; 16 dominant, 11 frequent, and 45 rare taxa, respectively. These results could be used as baseline to monitor, manage, and preserve neotropical fish species in their southern distribution boundary.

Longitudinal and temporal variation in fish assemblage structure along lowland prairie Neotropical streams and their relationship with environmental variables

“…Then, we hypothesize that the lower areas of Pampean streams provide essential functions for RdlP sh assemblages, just as oodplains do for rivers and streams. Indeed, riverine specimens recorded in lower sectors correspond to juvenile species identi ed as dominant and frequent for this system based on their abundance, biomass, and sampling occurrence (Maiztegui et al 2022). Since this phenomenon may be crucial in maintaining and regulating the ichthyofauna of the RdlP, further studies are necessary to understand the relevance of the interaction between the RdlP and its tributary streams.…”

“…Nevertheless, such gradients may be relevant in terms of stream functioning and longitudinal differentiation, because SRs located below ve m a.s.l. belong to the oodplain of the RdlP estuary and exhibit a strong tidal in uence of its riverine zone(Guerrero et al 1997; Cavalloto 2002;Cavallotto et al 2005;Maiztegui et al 2022). This phenomenon may cause physicochemical differentiation and high environmental variability in those stream sectors, and these predictions are supported by the results of ANOSIM and Anderson analyses in our study.…”