The present study compared vertebral deformities of hatchery-reared and wild-caught juvenile Japanese flounder,Paralichthys olivaceus.A total of 362 hatchery-reared flounder(total length 122.5-155.8 mm) were collected from three commercial hatcheries located in Yantai,East China,and 89 wild fish(total length 124.7-161.3 mm) were caught off Yangma Island near Yantai City(37°27′N,121°36′E).All the fish were dissected,photographed,and images of the axial skeleton were examined for vertebral deformities.Compared with wild-caught flounder in which no deformed vertebrae were detected,48(13.3%) hatcheryreared fish had deformed vertebrae.The deformities were classified as compression,compression-ankylosis,and dislocation-ankylosis.The vertebral deformities were mainly localized between post-cranial vertebra 1and 3,with vertebrae number 1 as the most commonly deformed.The causative factors leading to vertebral deformities in reared Japanese flounder may be related to unfavorable temperature conditions,inflammation,damage,or rupture to the intervertebral ligaments under rearing conditions.Furthermore,no significant difference in the total number of vertebral bodies was observed between wild-caught(38.8±0.4) and hatchery-reared flounder(38.l±0.9)(P>0.05).However,the number of vertebral bodies of hatchery-reared and wild-caught flounder ranged from 35 to 39 and from 38 to 39,respectively. The present study compared vertebral deformities of hatchery-reared and wild-caught juvenile Japanese flounder, Paralichthys olivaceus. A total of 362 hatchery-reared flounder (total length 122.5-155.8 mm) were collected from three commercial hatcheries located in Yantai, East China, and 89 wild fish (total length 124.7-161.3 mm) were caught off Yangma Island near Yantai City (37 ° 27’N, 121 ° 36’E). All the fish were dissected, photographed, and images of the axial skeleton were examined. for vertebral deformities. Compared with wild-caught flounder in which no deformed vertebrae were detected, 48 (13.3%) hatcheryreared fish had deformed vertebrae. the deformities were classified as compression, compression-ankylosis, and dislocation-ankylosis. vertebral deformities were mainly localized between post-cranial vertebra 1and 3, with vertebrae number 1 as the most commonly deformed. leading to vertebral deformities in reared Japanese flounder may be related to unfavorable temperatu re conditions, inflammation, damage, or rupture to the intervertebral ligaments under rearing conditions .Furthermore, no significant difference in the total number of vertebral bodies was observed between wild-caught (38.8 ± 0.4) and hatchery-reared flounder (38.l ± 0.9) (P> 0.05) .Wowever, the number of vertebral bodies of hatchery-reared and wild-caught flounder ranged from 35 to 39 and from 38 to 39, respectively.