Simple SummaryThis article discusses genetic traits (chromosomes, mtDNA) of the Amazon sailfin catfish. Domesticated fish of this species escaped from aquariums to establish invasive populations in large areas of North America and Asia. In Brazil, this species is an important fishery resource and a potential for fish farm management and production. Its karyotype showed 52 chromosomes with a similar conservative gross morphology to that of related species. The Cytochrome Oxidase I (COI) gene revealed a low molecular divergence between native and exotic populations.AbstractPterygoplichthys pardalisis an armored catfish native to South America and an important resource for the ornamental fish industry. Recently, several exotic populations have been introduced into rivers on five continents. Despite its commercial and environmental importance,P. pardalisis poorly studied from a genetic perspective. In this study, we analyzed the karyotype ofP. pardalisfrom the Amazon River and molecular variations in the mitochondrial gene Cytochrome oxidase I (COI) between native and exotic populations. The karyotype presented diploid number 2n = 52 and NF = 100 without cytogenetic variation between males and females. Nucleolus organizer regions (Ag-NOR) in the distal region of the long arm of pair 12 coincided with the 18S hybridization signal, whereas 5S was syntenic to this chromosome but localized in the short arm. The constitutive heterochromatin was restricted in the distal regions of pairs 4, 12, 25, and 26. Telomeric probes showed only distal hybridization signals. The karyotype ofP. pardalisdiverged from that of its congeners, and COI molecular variation revealed four haplotypes. The Philippine population revealed the greatest diversity with three haplotypes, while haplotype H1 was the most abundant and observed in both native and exotic populations. This new genetic data contributes to species management and provides useful information from an aquaculture perspective.