# Occurrence, Dominance, and Combined Use of Antibiotics in Aquaculture Ponds

## TL;DR

This study found that antibiotics are widely used in aquaculture ponds in China, with different types dominating in different seasons, raising concerns about environmental and health risks.

## Contribution

The study reveals seasonal shifts in antibiotic use and combined sulfonamide use in aquaculture, providing baseline data for sustainable practices.

## Key findings

- Enrofloxacin was the dominant antibiotic in August, with concentrations up to 2.36 µg/L.
- Sulfonamides like sulfamethoxazole and sulfadiazine became more common in October, with sulfadiazine reaching over 4 µg/L.
- Combined use of sulfonamides in autumn increases risks of antimicrobial resistance and ecological harm.

## Abstract

Antibiotics are commonly used in aquaculture to prevent disease, but their residues can remain in pond water and affect the environment. In this study, we measured sulfonamide and fluoroquinolone antibiotics in 40 aquaculture ponds around Wuxi, China, during two key farming stages: the summer grow-out period (August) and the autumn harvest (October). Using sensitive LC–MS/MS analysis, we found that antibiotics were widespread. Enrofloxacin, a fluoroquinolone, was dominant in August, occurring in over half the ponds at concentrations up to 2.36 µg/L. By October, sulfonamides such as sulfamethoxazole and sulfadiazine became more common, with one pond showing sulfadiazine levels above 4 µg/L. Statistical analyses confirmed a clear seasonal shift in antibiotic patterns and revealed that multiple sulfonamides were often used together in autumn. These results highlight two key issues: (1) different antibiotics dominate at different farming stages, and (2) combined use of drugs increases potential risks of antimicrobial resistance and ecological harm. To address these concerns, we recommend stricter monitoring and regulation, better farm management to reduce reliance on antibiotics, and promotion of alternative disease-control strategies. This study provides valuable baseline data for improving the sustainable and safe use of antibiotics in aquaculture.

Antibiotic use in aquaculture has become widespread to sustain production and control bacterial diseases, but it poses significant ecological and human health risks due to residue accumulation and resistance development. This study investigated the occurrence, dominance, and combined use of sulfonamide and fluoroquinolone antibiotics in freshwater fish aquaculture ponds around Wuxi, China. Here, the term aquaculture refers specifically to the controlled farming of freshwater fish species such as carp and crucian carp in managed pond systems. A total of 80 water samples (collected exclusively from pond waters) were obtained from 40 ponds during the high intensity rearing and harvest stage of fish. Residues of enrofloxacin and sulfonamide antibiotics were analyzed using a validated LC–MS/MS method with detection limits in the low nanogram-per-liter range. Results revealed that antibiotics were ubiquitous in pond waters, with enrofloxacin emerging as the dominant compound in August, reaching concentrations of up to 2.36 µg/L. By October, sulfonamides, particularly sulfamethoxazole and sulfadiazine, became more prevalent, with a maximum sulfadiazine concentration exceeding 4 µg/L. Multivariate analyses demonstrated a clear seasonal shift in antibiotic profiles, while correlation analyses indicated limited combined use in summer but notable co-occurrence of sulfonamides in autumn. These findings underscore that antibiotic application patterns in aquaculture are strongly linked to production stages, with potential consequences for environmental safety, resistance development, and food security. Effective monitoring, stricter regulation, and alternative disease management strategies are urgently required to mitigate risks and promote sustainable aquaculture practices.