Heritability and genetic correlations of growth traits in juvenile and adult olive flounder (Paralichthys olivaceus)

Growth traits are critical targets in aquaculture breeding, although their genetic architecture can vary across developmental stages. In this study, we examined stage-specific heritability, genetic correlations, and genomic associations of growth traits (body weight, BW; and body length, BL) in olive flounder ( Paralichthys olivaceus ), a high-value species farmed in East Asia. We genotyped 200 juveniles and 200 adults from 10 full-sib families using a 60K single-nucleotide polymorphism (SNP) array and evaluated BW and BL. Heritability estimates revealed a developmental contrast. Adult BW (h² = 0.485) and BL (h² = 0.427) showed moderate to high heritability, while juvenile BW (h² = 0.023) and BL (h² = 0.009) had near-zero values. Genetic correlation analysis supported these patterns. Adult BW and BL were strongly correlated (rg ≈ 0.95), whereas juvenile traits showed weak correlations, and cross-stage correlations with adult traits were consistently near zero. These findings suggest limited potential for early selection and highlight adult traits as more reliable targets for breeding programs. Genome-wide association studies (GWAS) were performed separately for juveniles and adults using mixed linear model (MLM) and Bayesian-information and linkage-dis-equilibrium iteratively nested keyway (BLINK) models. Significant SNP associations were consistently detected in adults but not in juveniles, likely reflecting low heritability, moderate sample size, and environmental noise during early development. In adults, GWAS identified 20 significant SNPs under the MLM model and 5 SNPs under the BLINK model, with 2 overlapping loci, resulting in 23 unique significant SNPs associated with growth traits. Candidate genes near significant SNPs included dot1l , mrps22 , megf6 , rgmd , and Tafa-1 , representing growth-related genomic regions. Collectively, our results suggest stage-specific genetic architectures of growth in olive flounder, provide candidate loci for molecular breeding, and indicate that breeding improvement may be more effective when focusing on adult traits with higher heritability and robust correlations. Future efforts should combine functional validation of candidate genes with large-scale GWAS to uncover small-effect variants, improve genomic prediction accuracy, and accelerate genetic gain in aquaculture.