<p>Introduction of non-native aquatic species may cause substantial adverse ecological impacts. Largemouth bass (<i>Micropterus salmoides</i>) is farmed with high production across a wide range of China, and pose a high invasion risk. Quantifying the contribution of wild (naturally spawned) and hatchery-reared individuals (artificially released) in field is critical to evaluate the invasion risk and establish an effective management system. For this purpose, otolith microstructure as a natural tag was used to establish a baseline by using known hatchery-reared and wild origins for separating these two origins of largemouth bass. Daily otolith increment width increased with age for wild and hatchery-reared individuals, but the significant difference between the two origins appeared since 9th day. The baseline model classified fishes with 84.91% accuracy. The result from the baseline model identified naturally spawned individuals across all field sample locations. Naturally spawned individuals occupied the majority except for a few locations, indicating a high invasion risk. The reconstructured spatial pattern of early increment width further provides essential data for a better assessment of invasion risk. The study further emphasizes that artificial release from various ways could increase invasion risk of largemouth bass in China, and the necessity to assess the ecological risk comprehensively and systematically.</p>