Mosaic environments shape the distribution of Neotropical freshwater ichthyoplankton

Abstract

Dam presence results in heterogeneous aquatic environments that probably favour segregation of ichthyoplankton developmental stages. Therefore, the present study tested the hypothesis that dams in the Upper Uruguay River create heterogeneous aquatic environments favouring segregation of ichthyoplankton developmental stages and also separate species with different reproductive tactics. Ichthyoplankton were captured bimonthly during 2002–2015 in 25 sampling stations grouped by fluviometric characteristics. Sampling was performed at night, with cylindrical–conical plankton nets and light traps. After quantifying ichthyoplankton, we identified larvae to the lowest possible taxonomic level and classified them based on developmental stage and reproductive tactics. Egg abundance was higher in lotic environments, preflexion individuals were more abundant in transitional lotic/lentic environments, and the flexion stage was predominant in lentic environments. Larval assemblages consisted mainly of sedentary species or those with short reproductive migrations. Species with similar reproductive tactics occurred in different environments. In conclusion, we provided evidence demonstrating that mosaic environments in the Upper Uruguay River are important for life cycle completion of different fish species. These distinct habitat zones allow for successful spawning and offspring development, thus guaranteeing recruitment.

Fish reproductive activity reveals temporal variations predominating spatial heterogeneity in maintaining high functional diversity of a Neotropical reservoir

“…Fish larvae have characteristics and environmental requirements that differ from those of adults in terms of habitat, feeding and behaviour (Leis & Trnski, 1989); they do not have the same functional characteristics as their parents. The occurrence of larvae in plankton is indicative of development sites in river systems (Humphries & Lake, 2000; Lopes & Zaniboni‐Filho, 2019), and their capture indicates that species reproductive activity occurs in the surrounding areas (Nakatani et al., 2001). Thus, documenting the spatial and temporal occurrences of ichthyoplankton can be a useful in studying the reproductive dynamics of fish populations.…”

Ontogenetic structure and distribution patterns of ichthyoplankton in the confluence zone of two river systems in the Eastern Amazon

“…Limnological factors have a strong relationship and synchronism with organisms, especially fish. They directly influence reproduction, occurrence and distribution of eggs and larvae, an integration that has been demonstrated in several studies (Lopes & Zaniboni‐Filho, 2019; Teixeira et al., 2019; Zacardi, Ferreira, et al., 2017), indicating that these environmental mechanisms can provide better conditions for growth and survival (Ponte et al., 2019; Zacardi et al., 2020).…”

“…Axes with eigenvalues greater than 1.0 were used for interpretation, according to the Kaiser-Guttman criterion (Gotelli & Ellison, 2004). Only limnological variables with score coefficients >0.4 were considered biologically important (Legendre & Legendre, 1998).…”

Diets and Trophic Structure of Fish Assemblages in a Large and Unexplored Subtropical River: The Uruguay River

“…This anthropogenic intervention in freshwater ecosystems typically results in the reduction of local biodiversity and affected community structure, particularly of fish [185,186]. For example, the low species richness and high spatial variability in the relative representation of different trophic groups in the upper Uruguay River might well be attributed to the presence of three hydroelectric dams between sampling sites (being this, a well-known impact of dams) [27,184,187]. Unfortunately, as there is a lack of baseline information on fish trophic structure it became impossible to disentangle the anthropogenic and natural effects driving fish trophic structure along the Uruguay River gradient.…”