| Quinolone drug is a kind of broad-spectrum antimicrobial agent which is used widely. Most of these drugs have lower MIC values on fish susceptible bacteria, higher drug concentration in tissue, and widely distributed, hence become one of the most important anti-infective drugs in aquaculture. For a long time, Quinolones (QNs) have turned out a large number of different categories, and took repeatedly or excessive dose, which has led to resistant strains, emerged unceasingly, resulting in increasing drug dosage and side effects. Moreover, the residues of such drugs have severe side effects to human, animals and fish, or even induced teratogenic and carcinogenic. Therefore, developing a rapid and effective detection method for QNs residues in aquatic products; researching the pharmacokinetics on enrofloxacin, one of the most commonly QNs, in crucians with different health conditions; and at the same time, studying the effect of enrofloxacin on the fatty acid composition of crucians; would contribute significantly to the monitoring the use of these drugs in aquaculture.An effective ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed for the trace analysis and validation of 20 quinolones in aquatic products. The extraction solvent, extracting way and clean-up method were researched. Four extraction solvents, three extracting ways and two clean-up methods were compared for the extraction and purification effects of QNs in aquatic products. The extraction rate of Mcllvaine buffer solution was highest, the extraction effect of ultrasonic extraction was best and the clean-up method of direct filtration was more effective. Several parameters of UPLC and MS/MS were optimized for determination of QNs. The linear range was from 3μg/kg to 300μg/kg for enrofloxacin, oxolinic acid, Pefloxacin, Pazufloxacin, Fleroxacin, from 0.5μg/kg to 500μg/kg for Nalidixic acid, Flimequine, from 1μg/kg to 100μg/kg for other 14 QNs with the good correlation coefficients (r≥0.9981). The lower limit of quantification was 0.34μg/kg to 8.13μg/kg. The recoveries were 63.6%～92.8%, with relative the standard deviations of 1.51%～11.32%, respectively, in spiked tissue samples at concentration levels ranging from 2.5μg/kg to150μg/kg of each quinolone. The method is simple, accurate and sensitive for the simultaneous determination of 20 QNs.Several comparative pharmacokinetic data such as absorption, distribution, and metabolism have been studied in this research on enrofloxacin in healthy and unhealthy crucian. The study results indicated that the blood concentration-time data of enrofloxacin in healthy and unhealthy crucian were best described by a two-compartment open model. The pharmacokinetic equations in blood:t1/2ka (0.42 h) and AUC(22.85μg/mL·h) healthy group was larger than those unhealthy, while t1/2β(7.18 h) and MRT(10.53 h) healthy group was smaller than those unhealthy group. Following oral gavage, the liver concentration-time data of enrofloxacin in healthy and unhealthy crucian were best described by a two-compartment open model. The t1/2ka in healthy and unhealthy groups were 0.47 h and l.27 h, respectively; t1/2βwere 23.71 h and 25.66 h,respectively; AUC were 85.77μg/mL-h and 26.13μg/mL-h, respectively; MRT were 10.53 h and 20.88 h, respectively. In the blood and liver of healthy crucians, enrofloxacin can be absorption, distribution and metabolism quickly. On the contrary, in unhealthy group, the absorption, distribution and metabolism were enrofloxacin slowly. After the concentration-time peak, enrofloxacin concentration in unhealthy blood and liver were decreased 67.16% and 52.31%, respectively. According to the MRL of enrofloxacin, it was advised that the withdrawal time following oral gavage healthy and unhealthy crucian were at least 3 d and 10 d, respectively.The crucian livers by oral administration of enrofloxacin as the object were study.total lipids of liver were extracted, and triglycerides, lecithin and cephalin prepared by TLC, and then the composition of the fatty acid was analyzed respectively by gas chromatography. The effect of enrofloxacin on fish liver from the perspective of fatty acid composition was investigated. The results showed that:After oral administration of such drug, the saturated fatty acid content in liver increased significantly, and polyunsaturated fatty acid content declined, which is similar to one of the clinical research reports that increasing the content of saturated fatty acids led to reduction in insulin sensitivity, while the content of C20:4-n6, in the total lipid fatty acid, was increasing, just as the related study, C20:4-n6 could activate the hepatic stellate cells; at the same time, monounsaturated fatty acids also showed a slow upward trend, just as the deficiency of peroxidase led to the transformation of fat into fat droplets. It could be predicted that after oral administration of enrofloxacin to crucian, enrofloxacin would adversely affect the fish liver, if long-time cross-use of enrofloxacin and other antibiotics in aquaculture, it is easy to cause fish liver damage or necrosis, ultimately leading to death.
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