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Simple Summary: In commercial aquaculture, aquatic animals are generally administered medicine ad libitum (at one's pleasure) via medicated feed. However, the estimation of withdrawal times for aquatic medicine is mostly carried out through the forced administration of medicine via oral gavage, which is not consistent with commercial aquaculture. This process may influence the absorption, distribution, metabolism, and excretion of medicine in aquatic animals and further affect the calculation of withdrawal times (WTs) for medicines. Therefore, in the current study, we selected the important aquatic medicine enrofloxacin (EF) to estimate its WTs in largemouth bass (Micropterus salmoides) after the administration of medicated feed. This study will obtain practical estimations of the WT of EF in actual aquaculture to aid in the surveillance of medication residue in fish products. The present study investigated the residue depletion and WTs of EF and its main metabolite, ciprofloxacin, in largemouth bass after ad libitum administration in commercial fish farming based on statistical approaches. Samples collected at pre-determined time points were assessed using high-performance liquid chromatography. If the concentrations of medicine were less than the quantitative limit, they were set to be half of the limit of quantitative. The terminal elimination of the target compound was assumed to fit a one-compartment model. The statistical methods of Bartlett's test and Cochran's test were used to inspect the homogeneity of the log-transformed data. The lack-of-fit test and F-test were used to check the linearity of the regression line. Outliers were assessed using standardized residuals. The final WT was estimated using the 95% percentile with a 95% confidence level. The WTs of EF were calculated to be 46, 29, 33, 46, and 20 days for the muscle + skin, plasma, gill, kidney, and liver, respectively. After the risk assessment, the values of the hazard quotient were calculated to be far less than 1, indicating that the risk of residual EF was particularly low in the edible tissues of largemouth bass after medicine depletion for various WTs. [ABSTRACT FROM AUTHOR]

Simple Summary: Enrofloxacin (EF) is an important antibiotic in global aquaculture. Due to the abuse and the emergence of drug resistance, the excess use of EF has occurred in recent years to result in residue exceeding in the edible tissues of aquatic animals. Withdrawal time (WT) is a red line to ensure food safety for humans. However, there is no related report of WT for EF in yellow catfish (Pelteobagrus fulvidraco). In addition to yellow catfish being sensitive to temperature, it can alter the disposition and elimination of EF and its main metabolite in fish bodies, ciprofloxacin (CF), thereby changing the WT in tissues. Therefore, we will conduct a WT estimation of EF in yellow catfish at different temperatures to establish related regulations to help residue surveillance in fish products. The objective of the present study was to investigate the residue depletion of EF and CF in yellow catfish to estimate its WTs in plasma and tissues after multiple oral doses for 3 days at 20 mg/kg at 15, 20, and 25 °C. Samples were collected at pre-designed time points after oral doses. A validated method was performed to quantify EF and CF in plasma and tissues by high-performance liquid chromatography. Statistical differences were conducted using one-way ANOVA analysis. According to the maximum residue limit of China and Europe considering 95% percentile with 95% confidence, the WTs were estimated to be 44, 72, 66, 99, and 95 days at 15 °C; 32, 66, 65, 86, and 73 days at 20 °C; and 32, 61, 64, 55, and 59 days at 25 °C in the plasma, muscle and skin, gill, liver, and kidney, respectively. We found that increased temperature shortened the WTs in plasma and tissues. Therefore, this study can help the risk assessment of EF in aquatic products for human health at different temperatures to avoid residue violation. [ABSTRACT FROM AUTHOR]

Tiamulin fumarate (TIF) is a pleuromutilin antibiotic and has high activity against animal bacterial pathogens including aquatic bacterial pathogens. However, its pharmacokinetic profiles, tissue distribution characteristics and bioavailability in aquatic animals remain unknown. The objective of this study was to investigate the pharmacokinetics and tissue distribution regularities of TIF in tilapia (Oreochromis niloticus) following a single oral (PO) dose of 20 mg/kg body weight (bw) and a single intravenous (IV) dose of 5 mg/kg bw at 22 ± 1°C, respectively. TIF concentrations in tilapia plasma and tissues were determined using the isotope dilution HPLC‐HESI‐MS/MS procedure, which was validated according to the guidelines defined by US Food and Drug Administration. TIF was well distributed throughout the body compartments of tilapia judged by the apparent volume of distribution (Vd) >1 L/kg (6.69 L/kg PO and 1.78 L/kg IV). TIF had a short mean residence time (MRT; 22.82 h PO and 14.61 h IV) and quick total body clearance (CLb) (0.62 L kg−1 h−1 PO and 0.60 L kg−1 h−1 IV). The total area under the curve (AUCtot) of plasma were 32.25 μg h−1 ml−1 (PO) and 8.30 μg h−1 ml (IV), respectively, and the oral absolute bioavailability (F%) of TIF was calculated to be approximately 97.1%. For tissue distribution, high concentrations of TIF were found in kidney, and the longest MRT was recorded in bile. The withdrawal time (WT) of TIF in muscle, skin, liver, kidney, gill, and bile was 3.75 (4) and 1.79 (2), 1.77 (2) and 2.06 (3), 6.41 (7) and 1.97 (2), 6.95 (7) and 3.98 (4), 4.92 (5) and 2.36 (3), and 7.06 (8) and 6.16 (7) days after PO and IV administration, respectively. The present investigations indicated that TIF was quickly absorbed, well distributed, rapidly eliminated in tilapia, and it could serve as reference data for establishing use regimen and provide useful information for the further development of TIF in aquaculture. [ABSTRACT FROM AUTHOR]

A fast ultra-performance liquid chromatography method was developed for the separation and quantification of doxycycline, 4-epidoxycycline, and 6-epidoxycycline in the muscles of channel catfish, shrimp, eel and turtle. The analytes were separated by comprehensive optimization of the chromatographic conditions. The extraction method was performed using a modified QuEChERS methodology. 2 g of muscle sample were mixed with 5 mL Mcllvaine buffer (pH 4), and 4 g of sodium sulfate and 2 g of sodium chloride were added for liquid-liquid partitioning. The mixture was agitated for 30 s and extracted with 10 mL of acidified acetonitrile. The resulting extract was purified using 200 mg of a C18-silica adsorbent. The samples were analyzed using ultra-performance liquid chromatography with ultraviolet detection using a BEH C18 column (2.1 mm ×100 mm, 1.7 μm). The limits of detection were less than 25 μg/kg and the limits of quantitation were less than 50 μg/kg for all analytes. The recoveries of the analytes were from 62.3% to 89.0% with relative standard derivations below 10.0%. The method provided efficient extraction and purification that enabled rugged and low-cost determination of the analytes. [ABSTRACT FROM AUTHOR]

Niclosamide is a mollusicide used for aquaculture on a large scale in China. However, it has high toxicity to aquatic animals and may cause damage to DNA. A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction procedure with high-performance liquid chromatography–heated electrospray ionization-tandem mass spectrometry method was developed for its determination. Samples were extracted with ammoniated acetonitrile, and anhydrous magnesium sulfate was added to remove moisture and precipitate proteins. The extracts were further purified with octadecylsilane. The recoveries of niclosamide in fortified muscle tissue at concentrations of 0.5 to 20 µg/kg were between 76.40% and 95.60% with relative standard deviations less than 9.54%. The limits of detection and quantification were 0.2 µg/kg and 0.5 µg/kg, respectively. The developed method was used to study the adsorption of niclosamide in channel catfish after administration. [ABSTRACT FROM PUBLISHER]

Simple Summary: Trichloroisocyanuric acid (TCCA) has been widely used in public health and aquaculture for the prevention and treatment of diseases. As a strong oxidative disinfectant, TCCA may cause adverse influences on aquatic organisms and further poses a threat to the aquatic ecosystems. Nonetheless, the toxicological influences of TCCA on aquatic animals are still scarce and the mechanisms of the toxicity at the molecular levels in goldfish (Carassius auratus) have not been illustrated. The current study investigated the influences of sublethal concentration of TCCA on transcriptomic responses, the molecular indices of oxidative stress, and histopathological alterations in the hepatic and gill tissues of goldfish. The results indicated that TCCA exposure induced the disturbance of energy metabolism and the detoxification process. Furthermore, TCCA exposure also induced oxidative stress in the liver and caused pathological damage in gills. These findings could be useful to help understand the toxicological influences of TCCA on goldfish. In this study, goldfish (Carassius auratus) were exposed to 0 (control group) and 0.81 mg/L TCCA for four consecutive days. The liver transcriptome, the molecular indices of oxidative stress, and gills histopathology were investigated. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that energy metabolism-related pathways such as glycolysis/gluconeogenesis were significantly enriched, suggesting their perturbation in the liver of goldfish. Additionally, TCCA exposure also caused pathological damage in gills, which compromised physiological function and decreased oxygen intake capacity of gills, thus leading to the enhancement of anaerobic metabolism. This finding was confirmed by the significant upregulation of lactate dehydrogenase in the liver of goldfish. Moreover, many phase I and phase II metabolic enzymes might be activated to alleviate TCCA-induced toxicity in goldfish, and glutathione S-transferases (GSTs) and cytochrome P450s (CYPs) play a crucial role in the metabolism of TCCA in the liver of goldfish. Furthermore, the antioxidant enzyme analysis showed that TCCA exposure induced oxidative damage in the liver and partially impaired the antioxidant defense system of goldfish, evidenced by decreased superoxide dismutase (SOD) and catalase (CAT), and increased malondialdehyde (MDA) level. In summary, this study will improve our understanding of the molecular mechanisms of the TCCA-induced toxicity in goldfish. [ABSTRACT FROM AUTHOR]

A liquid chromatography–tandem mass spectrometry quantitative method was developed for determining mebendazole and its metabolites, albendazole and its metabolites, and levamisole in muscles of bluntnose black bream, shrimp, eel and turtle based on modified QuEChERS methodology. The method included 2 g of the muscle matrix with 10 mL acetonitrile, and 0.8 g of magnesium sulphate and 0.2 g of sodium chloride for liquid-liquid partitioning. After vortex and centrifugation, the resulting liquid (5.5 mL) was purified by C 18 (50 mg) and Al-N (50 mg). The limits of detection were lower than 0.3 μg kg −1 and the limits of quantitation were no more than 1 μg kg −1 for all analytes. The recoveries of the analytes ranged from 80.0% to 113.7% with the relative standard derivation less than 10.0%. The preparation procedure provided efficient extraction and purification that enabled a sensitive and rugged determination of target compounds. [ABSTRACT FROM AUTHOR]