Genetic Diversity and Genetic Structure Analysis of Introduced and Selectively Bred Generations in Largemouth Bass ( Micropterus nigricans ) Based on Microsatellite Analysis

To assess the changes in genetic structure across generations of selectively bred largemouth bass ( Micropterus nigricans ) (F3, F4, F5, and F6), this study, in combination with an introduced population, utilized 15 pairs of microsatellite primers to analyze the genetic diversity and structure. The results revealed a total of 62 alleles ( N a ), with an average of 4.160 alleles per locus. The average observed heterozygosity ( H o ) was 0.559, and the average expected heterozygosity ( H e ) was 0.529. The introduced population exhibited the highest genetic diversity parameters, including polymorphic information content (PIC), N a effective number of alleles ( N e ), H o , H e , and Shannon’s information index ( I ). In contrast, the selectively bred populations showed a gradual decline, with PIC ranging from 0.398 to 0.494, N a from 3.533 to 4.000, N e from 2.008 to 2.387, H o from 0.480 to 0.589, H e from 0.457 to 0.550, and I from 0.794 to 0.990, indicating a moderate level of polymorphism. The F ‐test in different generations of selectively bred populations revealed that 10 loci had negative inbreeding coefficients ( F is ), while 5 loci had positive values, suggesting a low level of inbreeding across generations. Overall, the introduced and selectively bred populations exhibited a moderate level of genetic differentiation, with low to moderate genetic differentiation observed. AMOVA revealed that 92% of the variation originated within individuals. UPGMA clustering and PCoA analysis demonstrated significant genetic differentiation between the selectively bred populations and the introduced population. In conclusion, the introduced population exhibited higher genetic diversity compared to the selectively bred populations. The genetic diversity of the selectively bred populations showed a declining trend as the selection process progressed, highlighting the importance of evaluating genetic diversity while improving target traits during selection. This study provides scientific guidance for the selection of new varieties and the evaluation and conservation of germplasm resources in largemouth bass.