[Effects of Roxithromycin on Reproduction,Growth, and Anti-oxidation System of Daphnia magna]

Roxithromycin (ROX) is widespread in the water environment and has been reported to have ecotoxicological effects on aquatic organisms. To improve our understanding of these effects, we selected Daphnia magna as a test organism to study acute and chronic ROX toxicity on reproduction, growth, and antioxidant systems. The acute ROX toxicity was low, with 48 h-LC₅₀ and 96h-LC₅₀ROX values of 60.26 mg·L^-1 and 39.81 mg·L^-1, respectively. Furthermore, ROX concentrations of 0.5 μg·L^-1 and 50 μg·L^-1 significantly increased the frequency of egg laying, total number of eggs, and number of eggs per fetus. In the early exposure stages, ROX altered the sexual maturation time of Daphnia magna, affecting the frequency of egg laying and the number of eggs per fetus to cope with environmental stress. The intrinsic growth rate was also significantly increased by 50 μg·L^-1 ROX. In both treatment groups, Daphnia magna had a shorter body length, abnormal heart rate, and inhibited swimming activity. Moreover, 50 μg·L^-1 ROX inhibited the activities of POD, CAT, and GSH-Px by approximately 50% and induced MDA by more than 100%, resulting in the accumulation of reactive oxygen species in the body, which could potentially damage the cell membrane. In the 50 μg·L^-1 ROX treatment, per 06 was up-regulated, enhancing the immune response of Daphnia magna. In contrast. gst and gst-theta were down-regulated, suggesting that ROX could weaken the detoxification effect of Daphnia magna. jhe, ecra, ecrb, rxr, vg1, vg2, and vit-2 were also down-regulated. ROX affected the secretion of juvenile and thyroid hormones, inhibiting the synthesis of vitellogenin. Finally, ROX also affected the growth and disturbed the population stability of Daphnia magna. This study provides a reference for the effects of ROX on the reproduction and growth of aquatic organisms and their responses at protein and gene levels.