Ning Xu

The aim of this study was to establish an extrapolation physiologically based pharmacokinetic (PBPK) model of doxycycline (DC) to predict its withdrawal times (WTs) in yellow catfish ( Pelteobagrus fulvidraco ) and crayfish ( Procambarus clarkii ). The body weight, organ volumes, hematocrit, and plasma protein binding ratio were determined experimentally. Other parameters were cited from references or estimated by fitting pharmacokinetic data. A local sensitivity analysis was conducted to determine the sensitive parameter. WTs were predicted by Monto Carlo analysis. The final results demonstrated that the model simulation finely captured the depletion profile of DC in tissues and organs in yellow catfish (except for blood) and crayfish. The estimated WT of DC in the muscle of yellow catfish was 25 days, that was only 3 days longer than the measured value by the traditional method. The predicted WT in the muscle of crayfish was 43 days, being equal to the experimental value. Overall, this extrapolation model was successfully established among aquatic species to provide a novel and convenient tool for the surveillance of food safety.

The present study was conducted to establish population pharmacokinetics (PPK) of florfenicol (FLO) in crayfish ( Procambarus clarkii ) after a single oral administration at a dose of 15 mg/kg at 25°C based on a nonlinear mixed effect model. The sparse sampling method was used to collect the blood samples. Thirty‐two crayfish were divided into four groups, and one group included four male crayfish and four female crayfish. One animal undertook three sampling time points. All samples were quantified using high‐performance liquid chromatography with an ultraviolet detector. The initial pharmacokinetic (PK) parameters were estimated by reference search and the calculation of a naïve pooled approach. The additive error model was selected using the tool of maximum likelihood model comparison. The covariate model included the two variations of body weight and sex. Through the addition and subtraction of parameters, weight and gender had no significant effect on the alterations of PK parameters. Afterward, the random effects were introduced in the model, which notably reduced the coefficient of variation. Finally, the calculated values of the absorption rate constant, apparent distribution volume, and total systemic clearance were estimated to be 1.93/h, 11.16 L/kg, and 2.35 L/h/kg, respectively. The secondary parameters of the elimination rate constant, elimination half‐life, and area under the concentration‐time curve were calculated to be 0.20/h, 3.47 h, and 6.38 h.mg/L, respectively. This study supported a concise method for conducting PK studies in crustacean animals that facilitated the development of PK methodology in aquaculture.

This preclinical study investigated the efficacy and safety of fenbendazole, a broad-spectrum benzimidazole anthelmintic, for the treatment of Gyrodactylus kobayashii in goldfish (Carassius auratus). In vivo bath treatments demonstrated potent, dose-dependent anthelmintic efficacy, achieving 98.58% efficacy at a concentration of 0.02 mg/L and a 48 h EC₅₀ of 0.006 mg/L. A short-duration (6 h) bath at 0.06 mg/L, followed by an 18 h recovery period in dechlorinated water, resulted in complete parasite elimination. However, acute toxicity assay indicated a relatively narrow safety margin for prolonged bath treatments, with a 96 h LC₅₀ of 0.039 mg/L, highlighting the need for caution when employing extended bath treatments. Oral administration of fenbendazole at 20 mg/kg body weight for three consecutive days resulted in an efficacy of 83.35%, which increased to 96.28% by seven days post-treatment. Safety evaluations revealed this regimen induced transient oxidative stress and mild, reversible histopathological alterations in the liver and gills. Biochemical and histological markers indicated a recovery trend, approaching baseline levels by 15 days post-treatment. These findings suggested that oral fenbendazole is an effective and relatively safe anthelmintic treatment against G. kobayashii in goldfish. This study underscores the potential of drug repurposing as an effective strategy for developing novel anthelmintic agents in aquaculture.

This study aimed to investigate the PPK of EF in largemouth bass after oral and intravenous administration based on a nonlinear mixed effect model. Samples were collected using the sparse sampling method at pre-designed time points determined by high-performance liquid chromatography with a fluorescent detector. The initial PK parameters were estimated by reference search and the calculation of a naïve pooled approach. The covariate model included a variation in body weight. The oral dose data were best fitted by a one-compartment model. The injection dose data were best fitted by a two-compartment model. The results demonstrated that body weight had no marked effect on the parameters of PPK. Finally, the bioavailability was calculated to be 12.24%. The area under the concentration–time curve/minimum inhibitory concentration was estimated to be ≥408.16, indicating that EF at 20 mg/kg has high effectiveness for aquatic pathogens.

Aeromonas hydrophila (A. hydrophila) is an opportunistic and foodborne pathogen widely spread in the environments, particularly aquatic environments. Diseases caused by A. hydrophila in freshwater aquaculture result in huge economic losses every year. The increasing emergence of antibiotic resistance has limited the application of antibiotics in aquaculture. Aerolysin (AerA), the main virulence factor produced by A. hydrophila, has been identified as a promising target for developing drugs controlling A. hydrophila infection. Here, we found that the natural compound amentoflavone (AMF) with the MIC of 512 μg/mL against A. hydrophila could dose-dependently reduce the hemolysis of AerA, ranging from 0.5 to 4 μg/mL. Molecular docking and dynamics simulation results predicted that AMF could directly bind to domain 3 of AerA via Pro333 and Trp375 residues. Then, the binding sites were confirmed by fluorescence quenching assays. The results of heptamer formation demonstrated that the binding of AMF could affect the formation of oligomers and result in the loss of pore-forming activity. Cell viability assay showed that AerA after treatment with AMF ranging from 0.5 to 4 μg/mL could significantly reduce AerA-mediated cytotoxicity. Moreover, experimental therapeutics results showed that channel catfish infected with A. hydrophila and then administered with 20 mg/kg AMF at intervals of 12 h for 3 days could increase the survival rate by 35% compared with the positive control after a 10-day observation. These findings provided a novel approach to developing anti-infective drugs and a promising candidate for controlling A. hydrophila infection in aquaculture.

The objective of this study was to implement population pharmacokinetic (PPK) of enrofloxacin (EF) in grass carp (Ctenopharyngodon idella) after a single oral administration and a single intravenous administration based on a nonlinear mixed effect model. The plasma samples collected by the sparse sampling method were detected by high‐performance liquid chromatography with a fluorescent detector. The initial pharmacokinetic (PK) parameters were evaluated by reference search and the calculation of a naïve pooled method. After oral administration, the concentration–time profile was best described by a one‐compartment open model. The absorption rate constant (K_a), apparent distribution volume (V), and systemic clearance (CL) were estimated to be 3.11/h, 4.36 L/kg, and 0.079 L/h/kg, respectively. After intravenous administration, the concentration–time curve was best simulated by a two‐compartment open model. The apparent distribution volume of the central compartment (V₁), apparent distribution volume of the peripheral compartment (V₂), CL, and clearance from the central compartment to the peripheral compartment (CL₂) were estimated to be 0.42, 2.05 L/kg, 0.067, and 2.94 L/h/kg, respectively. Finally, the bioavailability was calculated to be 84.81%. The parameter of AUC/minimum inhibitory concentration value was estimated to be more than 506.32 for Aeromonas hydrophila, Aeromonas sobria, and Flavobacterium columnare indicating that EF at 20 mg/kg has high effectiveness for these pathogens. This study supported a concise method for conducting PK study in aquatic animals that facilitated the development of PK methodology in aquaculture.

The purpose of this study was to measure organ blood flow (OBF) in yellow catfish (YC, Pelteobagrus fulvidraco), largemouth bass (LB, Micropterus salmoides), and grass carp (GC, Ctenopharyngodon idella) using the method of fluorescent microspheres. Yellow–green microspheres were injected into the fish via cardiac catheterization using a syringe pump at a rate of 0.8 mL/min. Reference blood samples were collected from the dorsal aorta, and fish tissues were harvested after 5 min and processed for fluorescence spectrophotometric analysis. The results showed that the OBF of the heart increased significantly with the increase in temperature from 20 to 30 °C, while there was no significant difference in the OBF of other organs/tissues in YC. The OBFs of different species of LB and GC were also determined at 25 °C. In GC, the blood flow rates of the heart, spleen, kidney, liver, others, gills, swim bladder, intestines, muscles, and skin were 9.55, 1.00, 10.3, 6.92, 6.70, 6.04, 2.06, 2.81, 1.78, and 3.72 (mL/min/g), respectively. In LB, the blood flow rates of the same organs were 8.80, 2.33, 1.01, 0.71, 4.11, 2.72, 1.22, 0.54, 9.47, and 0.40 (mL/min/g), respectively. Compared to the OBFs of YC at 25 °C, the OBFs in GC were the highest, followed by LB. These results reflect that OBF in fish has significant species differences. These studies provide fundamental physiological data on OBFs in YC, GC, and LB, which has practical implications for improving the development of disciplines associated with fish physiology.

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.

Enrofloxacin (EF) is a broad-spectrum and highly efficient antibiotic commonly used for treating diseases in aquatic animals. However, its abuse in aquaculture applications often leads to excess residue in tissues of grass carp (Ctenopharyngodon idella). Hence, this study aimed to estimate the withdrawal time (WT) of EF and its metabolite of ciprofloxacin (CF) administered medicated feed in natural culture environments and conduct a risk assessment. Plasma and tissue samples were gathered at appropriate time points and detected by high-performance liquid chromatography. The data homogeneity was evaluated by Bartlett’s test and Cochran’s test. The linearity of the regressed line was evaluated by visual inspection and F test. Outliers were estimated on a normal probability scale by plotting the standardized residual versus their cumulative frequency distribution. Finally, the WT was calculated to be 51 days in muscle + skin based on the maximum residue limit of 100 µg/kg. After 51 days, the concentration of EF and CF fell below 10 µg/kg. The estimated daily intake was calculated to be 0.009 µg/kg/d. Hazard quotient was computed to be 0.002, which was far below one. These results suggested that calculated WT of EF could ensure the safety of products from grass carp for humans.

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.