Beyond Occurrence: Evidence Gaps for Non-Native Freshwater Fishes in Brazilian Drylands

Abstract

Non-native freshwater fishes are widely reported in inland waters, but occurrence records are often interpreted together with stronger evidence of establishment, reproduction, spread, pathways and impacts. This can overstate what published records support, especially in regions where reservoirs, river-basin transfers and artificial connectivity complicate biogeographic interpretation. We reviewed published evidence on non-native freshwater fishes in Caatinga-associated aquatic systems of the Brazilian semi-arid region. Searches in Scopus, Web of Science and SciELO retrieved 508 records; after screening and full-text assessment, 65 studies were included. Each study or species-record was coded in a structured evidence matrix for spatial coverage, habitat type, taxonomic identity, author terminology, biogeographic status and evidence dimensions. Occurrence was the dominant evidence type, whereas establishment, reproduction, spread, pathways and impacts were less frequently documented. Reservoirs, dams and river-basin contexts were the most common settings, although natural systems, coastal drainages and water-transfer systems also contributed to the evidence base. Cichlids (six named species), poeciliids (four species) and sciaenids (one species) concentrated many species-records. The review separated species exotic to Brazil from species native to Brazil but recorded outside their expected basin or drainage. This distinction helps avoid treating all non-native records as evidence of invasion. The findings show that assessments of non-native freshwater fishes should distinguish presence from persistence, reproduction, dispersal, pathway and ecological effect. The proposed evidence framework can support monitoring, data review and management decisions in freshwater systems where introductions, basin transfers and artificial connectivity complicate interpretation of non-native records.