Invisible dynamics: exploring the genetic diversity of peacock bass in Brazil

In Brazil, the introduction of non-native species into freshwater environments, such as peacock bass (Cichla spp.), was driven by aquaculture and sport fishing. These Amazonian fish possess phenotypic plasticity and resilience that facilitate their invasion and establishment in new habitats. Due to the taxonomic complexity of cichlids, studies on intraspecific variation are essential to mitigate the impacts of biological invasions. This study aimed to analyze the genetic diversity of peacock bass, assessing how invasive populations have diversified over time and across different regions in Brazil. Samples were collected from different invasive populations in Maranhão, São Paulo, Paraná, and Goiás. DNA was extracted and the 16S and COX1 genes were amplified. Ninety-seven specimens of the genus Cichla Schneider, 1801 were identified as Cichla monoculus Agassiz, 1831 (n=12); Cichla kelberi Kullander and Ferreira, 2006 (n=75); and Cichla piquiti (Kullander and Ferreira, 2006) (n=10). Sixteen 16S haplotypes (445bp) were identified, with haplotype diversity and nucleotide diversity values of Hd: 0.830 and Pi: 0.03777, respectively. The results showed proximity between the invasive populations from Maranhão and São Paulo, with haplotype sharing among Parque Nacional dos Lençóis Maranhenses, Baixada Maranhense, and Ilha Solteira. This highlights the fragility of species delimitation and definitions within the group, based solely on morphological data. By evaluating the set of morphological and genetic data, we found significant intraspecific variations, despite expecting population homogeneity due to the founder effect and bottleneck commonly observed in invasive populations. This underscores the adaptive potential of these cichlids.