Amazonian ichthyoplankton assessment via DNA metabarcoding: A baseline for detecting spawning sites of migratory fishes

The Neotropical fish fauna comprises approximately 6080 species, of which almost 3000 inhabit the Amazon River basin. However, the construction of hydroelectric dams has threatened this biodiversity by habitat fragmentation. To uncover the putative effect of river impoundment on migratory fish species, over 5400 eggs and larvae were collected from the Teles Pires River, including five tributaries and the hydroelectric reservoir, which were identified using the COI metabarcoding approach. Identification of early life stages allowed the detection of >40 fish species, including at least 27 migratory species. Fish eggs were assigned to nine families, 13 genera, and 23 species, whereas larvae were attributed to 12 families, 18 genera, and 34 species. Eggs and larvae of migratory fishes were primarily present in tributaries upstream of the dam, with fewer in the reservoir. A putative impact of the dam on the ichthyoplankton community was detected, with a significant difference found between the reservoir and tributaries for larval species richness (r = 0.822, p = 0.0211). In contrast, no significant difference was recovered among tributaries for both eggs (r = 0.213, p = 0.2657) and larvae (r = 0.378, p = 0.0696). However, a change in ichthyoplankton assemblage was observed between tributaries, as revealed by beta diversity analyses. These results highlight the potential of ichthyoplankton metabarcoding for studying and biomonitoring of migratory fishes, as well as providing relevant data concerning the identification of spawning sites to set guidelines for fisheries management and effective conservation of fish populations.