First record of the “Matrinxã” Brycon amazonicus (Agassiz 1829) (Characiformes: Bryconidae) in the Rio Paranapanema mouth region, Upper Rio Paraná basin, Brazil

Abstract: The Rio Paranapanema is one of the most important tributaries of the Upper Rio Paraná, and in recent decades there has been a marked decline in the population of native species due to the development of a series of reservoirs and the introduction of many non-native fish species. This study presents the first record of the non-native Brycon amazonicus in the mouth region of the Rio Paranapanema. One specimen was collected in May 2024 in the Porto Maringá region, Marilena municipality, Paraná state, Brazil. The specimen was euthanized with benzocaine, fixed in 10% formalin, and later preserved in 70% ethanol. Morphometric measurements were taken using a digital caliper, and meristic data were recorded according to specific literature. Our results show that the Brycon specimen collected in the region of the mouth of the Rio Paranapanema fits the diagnosis of the non-native Brycon amazonicus. The presence of this species raises concerns regarding its potential impact on native Brycon species, especially Brycon orbignyanus, which is critically endangered. Introduction of Brycon amazonicus in this region may be associated with accidental escapes from aquaculture, sport fishing, or stocking programs in reservoirs. The record of Brycon amazonicus in this highly impacted environment underscores the need for continuous monitoring and management strategies to mitigate potential threats to native ichthyofauna and preserve the ecological integrity of the Upper Paraná ecoregion.