Largemouth bass Micropterus salmoides , native to the Southeastern United States, has shown extreme economic and ecological significance throughout the North American continent . This species has gained access to a large area of habitats outside its native range , having been introduced to many countries in Asia, Europe, and Africa since the 19th century , and has played a great role in aquaculture, freshwater fisheries, and ecological systems of these regions. Identification of the population origin of an introduced species is a prerequisite for testing hypotheses concerning the factors responsible for its breeding and control.
In the present study, a total of 1,125 individuals from 28 sampling sites were collected. Two sites were located in the Guangdong province, where largemouth were introduced in 1980's for aquaculture in China. The genetic structure of largemouth bass distributed in the United States was evaluated, and the origin of the cultured M. salmoides populations in both the United States and China were inferred based on microsatellites data. The results showed that largemouth bass populations collected from native areas were mostly assigned into two genetic clusters, while some populations were admixed to some extent . Most individuals of cultured populations collected from Zhanjiang and Guangzhou, China, as well as cultured populations from Piketon (OH), North MC Fish Hatchery (Mississippi), and Lake Kickapoo (Texas) in the United States probably came from n orthern strains; while most individuals of populations collected from the Turcotle Fish Hatchery (Mississippi) were probably from s outhern strains. Interestingly, the cultured populations collected in this study showed relatively pure genetic source, while some natural populations were admixed to some extent .