Abstract：The aim of the study was to explore the effects of photoperiod and red light irradiation on ovarian development of a stream fish, Acrossocheilus fasciatus. The interactive experiment with two factors and two levels was designed basing on the different photoperiods (12L∶12D and 16L∶8D) and light colors (white and red). Gonadosomatic index (GSI), the proportion of developing oocytes in each stage, plasma melatonin (MT) levels, and malondialdehyde (MDA) contents and superoxide dismutase (SOD) activity of muscle and liver were investigated in the pre-breeding females. The results showed that the maximum of GSI and the percentage of developing oocyte at stage Ⅲ occurred in the fishes under long photoperiod (LP) with red light, but the minimum in those under shot photoperiod (SP) with white light (P < 0.05) (Fig.2). The maximum level of night plasma MT was found under LP with red light condition, while the minimum level was under the SP with white light condition (P < 0.05) (Fig.3). Neither photoperiod nor light color had a significant influence on muscular MDA contents and SOD activities of muscle and liver. However, hepatic MDA contents were significant increased by LP and red light (P < 0.05) (Fig.4). The interaction effect between photoperiods and light colors was detected in the most biological indicators. As a conclusion, long photoperiod with red light could significantly improve ovary development accompanied with the increase of plasma MT level, which suggested that MT played a crucial role in regulating reproduction in this species.