Abstract
Growth is a key genetic improvement target in aquaculture. The giant grouper (Epinephelus lanceolatus), the largest and fastest-growing grouper species, is an important aquaculture species and also an ideal male parent in grouper hybrid breeding, such as hulong hybrid grouper (E. fuscoguttatus ♀ × E. lanceolatus ♂). However, the genetic basis of this rapid growth is unclear. In this study, we established a hulong hybrid grouper self-cross population, observing significant growth segregation. Using Bulked Segregant Analysis (BSA) and RNA-seq on extreme growth groups, we identified a significant growth-related quantitative trait locus (QTL) on chromosome 2, containing 23 candidate genes and 5 growth-correlated non-synonymous SNPs. Transcriptome analysis revealed 4074 differentially expressed genes. Integrating these results, we identified three critical genes: iqgap1, mex3b, and ndufs3, involved in cell proliferation, embryonic development, and energy metabolism, respectively. Their expression patterns further supported their association with giant grouper's rapid growth. Our findings provide crucial insights into giant grouper growth mechanisms and valuable molecular markers for grouper breeding.