Drifting in a free-flowing river: Distribution of fish eggs and larvae in a small tributary of a Neotropical reservoir

Abstract

We investigated spatial and temporal variations in the distribution of fish eggs and larvae in the Guareí River, a free-flowing tributary located in the upper section of the Jurumirim Reservoir, Paranapanema River, Brazil. Fish eggs and larvae were sampled ~ fortnightly from November 2017 to March 2018 (Cycle 1), and from November 2018 to March 2019 (Cycle 2), at three sites distributed along the entire course of the Guareí River. We collected 859 fish eggs and 1,340 larvae, comprising 19 taxa. We found reproductive activity of several fish species in the Guareí River, including long-distance migrants. However, there was no spatial differences in the assemblage structure and densities of fish eggs and larvae along the channel of Guareí River. We recorded temporal differences in larvae density only in Cycle 2. The consistent capture of fish eggs and larvae in two reproductive cycles is strong evidence that this river is a spawning site for a variety of fish species. Thus, we recommend maintaining its natural flow regime.

Inadequate Sampling Frequency and Imprecise Taxonomic Identification Mask Results in Studies of Migratory Freshwater Fish Ichthyoplankton

“…This factor was particularly evident in the significant temporal and spatial variation observed in ichthyoplankton composition. Ichthyoplankton studies conducted in neotropical rivers have commonly adopted biweekly or longer sampling intervals, e.g., [24,25,[46][47][48]. Incomplete identification becomes even more critical when we consider the fish monitoring programs developed by the hydroelectric sector.…”

“…Most South American river basins, which harbor an enormous biodiversity of fish, are already highly fragmented [54]. In these systems, free-flowing river segments are refuges for migratory species, some of which are rare and/or threatened [11,24,47,48,55]. In this context, the identification of critical habitats, especially spawning sites, is essential for taking appropriate conservation measures.…”