Changes in Body Growth and Growth-Related Genes under Different Photoperiods in Olive Flounder, Paralichthys olivaceus

This study examined the effects of different photoperiod conditions on olive flounder (Paralichthys olivaceus), a commercially important species in Korea. Daily variations in the expression of mRNA for the growth-related genes ary­lalkylamine N-acetyltransferase2 (AANAT2), preprosomatostatin1 (PSS1), and growth hormone (GH) were examined under a 12 h light:12 h dark photoperiod. All the genes were expressed at higher level during the dark period. Melatonin injections increased the expression of GH, but did not significantly affect the expression of PSS. Under short-day conditions (10 h:14 h), the fish gained more weight than under long-day conditions (14 h:10 h). A long nighttime induced melatonin secretion and increased the expression of GH mRNA, promoting weight gain in this species. Therefore, we thought that the long day condition in raising olive flounder may be effective in inducing body growth.