A new Korean genotype of bluegill Lepomis macrochirus (Centrarchidae) covering the Korean Peninsula: insights for management of an introduced freshwater fish

Background: Lepomis macrochirus Rafinesque, 1819—commonly known as the bluegill—is an invasive freshwater fish native to North America, first introduced to Japan in 1960 and subsequently to Korea in 1969. Objective: To assess the diversity of L. macrochirus haplotypes in Korea using mtDNA ND1 and to examine how these haplotypes are distributed across the country, searching for evidence of new introductions or local mutations. Methods: In this study, we examined 100 individuals collected from 14 sites across five Korean regions, focusing on mitochondrial ND1 haplotype variation to clarify the species’ genetic diversity and structure. Results: Population genetic analyses revealed relatively low haplotype diversity (0.568) and nucleotide diversity (0.00065), indicative of a founder effect typical of invasive species. In L. macrochirus, three distinct haplotypes were identified: Lm1, Lm3, and a newly detected, Korea-specific LmK. Conclusions: Phylogenetic and population genetic results suggest that LmK evolved from Lm1. Lm1 (47%) and LmK (46%) were the most prevalent overall, while Lm3 was detected in only 7% of samples. Notably, LmK was found in all sampled regions except Jeju Island, indicating rapid, likely human-mediated dispersal across geographically isolated freshwater systems. The identification of this novel haplotype suggests that novel genetic variants may arise even within genetically narrow introductions. These findings expand our understanding of the species’ genetic structure and spread in Korea, emphasizing the importance of continued genetic monitoring and targeted management strategies.