Effects of Water Temperature and Photoperiod on the Antioxidant Status and Intestinal Microbiota in Larval Spotted Mandarin Fish, Siniperca scherzeri, in the Yalu River

Antioxidant capacity and intestinal microbiota play a crucial role in the nutrition, immunity, and overall health status of fish. It is significant to understand the impact of environmental changes on the health of <i>Siniperca scherzeri</i>, an important breeding species. Therefore, in order to investigate the effects of photoperiod (8L: 16D, 12L: 12D and 16L: 8D) and water temperature (18 and 28 °C) on the antioxidant capacity and intestinal microorganisms of <i>S. scherzeri</i>, liver and intestinal samples from cultured juvenile <i>S. scherzeri</i> were collected for related analyses. The photoperiod group of 12L: 12D and the water temperature group of 18 °C presented a higher abundance of Malondialdehyde (MDA) and lower abundances of Superoxide dismutase (SOD), Glutathione peroxidase (GSH-Px), and Catalase (CAT) than other groups (<i>p</i> < 0.05). No significant difference in intestinal microbial diversity was found among different groups (<i>p</i> > 0.05), except that the ACE index showed significant differences among different temperature groups (<i>p</i> < 0.05). Significant differences in the relative abundances of <i>Proteobacteria</i> and <i>Tenericutes</i> were found among different groups (<i>p</i> < 0.05). Modifying the duration of light exposure could effectively mitigate oxidative reactions and optimal high temperatures could suppress oxidation in juvenile <i>S. scherzeri</i>. However, these conditions also influenced the feeding behavior of juvenile <i>S. scherzeri</i> and the composition of intestinal microbiota and promoted the proliferation of opportunistic bacteria. The study provides the valuable data of the aquatic habitat of <i>S. scherzeri.</i>