Keywords: 
• antibiotics /
• fish /
• aquaculture products /
• Beijing market

Abstract: To survey the contamination level of antibiotics in aquatic products in Beijing market, crucian carp, carp, grass carp and chub of different weights were sampled from several major farmer markets in Beijing and ten antibiotics including tetracycline, sulfa antibiotics and quinolones were analyzed by based on ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The result showed that only four antibiotics, i. e. sulfamethazine, marbofloxacin, norfloxacin and enrofloxacin, could be detected in some fish samples (2.1%, 4.2%, 16.7%, 46.9% detection rate), while others were below detection limits. Among the detected norfloxacin and enrofloxacin in crucian carp, carp, grass carp and chub, with the concentration of antibiotics, sulfamethazine and marbofloxacin were only detected in grass carp, while enrofloxacin in carp significantly higher than crucian carp, followed by grass carp and chub, respectively. Only enrofloxacin in fish samples exceeded the maximum residue level (MRL in NY5070-2002, 50 μg·kg^-1). The concentrations of sulfamethazine, marbofloxacin and norfloxacinwere higher in larger fish (with the highest concentration of 34.8、179.6、39.4 μg·kg^-1) and not detected in small fish, indicating the accumulation processes. In general, aquatic fish products in Beijing market showed contaminated by antibiotics, while their residuals were mostly below MRL values. Best management practice is needed in cultivating fishery and in antibiotics usage.