) by applying hydrostatic pressure to the eggs of Japanese flounder following fertilization with UV-treated sperm from red sea bream (used as a mapping family). We measured the size of six component elements of the cephalocaudal axis, including body length, head length, dorsal fin length, pelvic fin length, caudal peduncle length, and caudal length. The values for these six traits were all normally distributed and were significantly correlated (<0.01).We documented 22 quantitative trait loci (QTL) controlling the six growth-associated traitsusing MapQTL4.0. These QTLs were mapped on 10 of 24 linkage groups. Among these, four QTLs were correlated to body length, three to head length, four to dorsal fin length, three to pelvic fin length, seven to caudal peduncle length, and one to caudal length. The LOD values of these QTLs varied between 2.01 and 3.68, which explained 3.7%–12.6% of the phenotypic variation. QTLs for body length and caudal length were co-localized; and QTLs for body length, dorsal fin length, and pelvic fin length were also co-localized. Our results provide insight for further selective breeding research and breed improvement.