To effects of sex maturation in olive flounder by regulating long photoperiod, gonadal development and GTH mRNA expression in the pituitary were investigated. Photoperiod was treated natural photoperiod and long photoperiod (15L:9D) conditions from September 2011 to March 2012. The results showed that natural photoperiodic group showed a higher gonadosomatic index (GSI) than long photoperiodic group during the spawning season (March 2012). The histological analysis of ovarian tissue showed that natural photoperiod group of ovaries contained vitellogenic oocytes, but long photoperiod group of ovaries mainly contained perinucleolus staged oocyte and oil-drop staged oocytes. The FSH mRNA of olive flounder, under natural photoperiod group, showed a significantly higher expression but no significant difference under long photoperiod group. The LHβ mRNA showed a significantly higher expression only under natural photoperiod group. These results may suggest that long photoperiodic information regulates secretion of pituitary FSH and LH and maintain early growing stage of gonadal development in this species.

• Byeong-Hoon Kim(Marine and Environmental Research Institute, Jeju National University)
• Chi-Hoon Lee(Marine and Environmental Research Institute, Jeju National University)
• Sang-Woo Hur(Marine and Environmental Research Institute, Jeju National University)
• Sung-Pyo Hur(Marine and Environmental Research Institute, Jeju National University)
• Dae-Hwan Kim(Department of Oceanography, Chonnam National University)
• Hae-Lip Suh(Department of Oceanography, Chonnam National University)
• Sung-Yeon Kim(Genetics & Breeding Research Center, National Fisheries Research & Development Institute)
• Young-Don Lee(Marine and Environmental Research Institute, Jeju National University) Corresponding Author