Congcong wu ^1,2,3 Haitao Ye ^4* Mingzhu Xu ^3* Xuan Zhao ^3* Xuejie Zhao ^3* Lina Li ^3* Mingzhi Li ^3* Yanfei Wei ^3* Yuru Li ^3* Baolan Hu ^1,2*

• ¹ Zhejiang University, Hangzhou, China
• ² Key Laboratory for Water Pollution Control and Environmental Safety Zhejiang Province, Hangzhou, Zhejiang Province, China
• ³ Zhejiang Environmental Technology Co., Ltd, Hangzhou, Jiangsu Province, China
• ⁴ Zhejiang Qingke Environmental Protection Technology Co., Ltd, Quzhou, China

The growing demand for aquaculture products has led to increased density and scale in aquaculture, resulting in higher requirements for feed, antibiotics, vaccines, and other substances, which makes aquaculture an important source of antibiotics and ARGs in environmental waters. However, the occurrence of antibiotics and ARGs under different modes and stages of aquaculture has rarely been systematically studied. In this paper, we investigated the dynamics of major antibiotics, ARGs, bacterial diversity, and their interrelationships in the water bodies at different stages of three major freshwater aquaculture modes (traditional pond, raceway system, and ecological modes) in the south Tai Lake (China). The results showed that quinolone and chloramphenicol were the main antibiotics, and the highest absolute abundance genes were quinolone resistance genes (qnrB) and quinolone resistance genes (sul1), with the mobile genetic element (MGE) intI1, both of which exhibited a gradual seasonal increase. Microbial diversity also varies seasonally, especially with a gradual increase in the abundance of some pathogenic bacteria (Flavobacterium). Antibiotics and resistance genes were found at higher levels in fish ponds compared to shrimp and crab ponds, while they were lower in shrimp and crab ponds that utilized the ecological mode ponds than in the traditional culture mode ponds. The used strategy of antibiotics alters the subtypes of ARGs within the same class, and low concentrations of sulfonamide antibiotics instead promote the spread of corresponding ARGs rather than in situ degradation. Overall, this study presents a comprehensive characterization of antibiotics and ARGs in aquaculture waters from various perspectives. These findings will support the optimization of aquaculture mode and antibiotic usage to finally contribute to the green and sustainable development of aquaculture.