The objective of this study was to demonstrate the pharmacokinetic–pharmacodynamic profile, bioavailability, and withdrawal time of tylosin tartrate (TT) administered to olive flounder via intramuscular (IM, 10 or 20 mg/kg, n = 240) and intravascular (IV, 10 mg/kg, n = 90) injections. Serum concentrations of tylosin were determined using a validated liquid chromatography-tandem mass spectrometry method. According to the non-compartmental analysis, the bioavailability of TT was 87%. After the IV injection, the terminal half-life, total body clearance, volume of distribution, and mean residence time of TT were 21.07 h, 0.07 L/kg/h, 2.15 L/kg, and 16.39 h, respectively. Rapid absorption (T_max 0.25 h), prolonged action (terminal half-life, 33.96 and 26.04 h; MRT, 43.66 and 33.09 h), and linear dose–response relationship (AUC_0-inf, 123.55 and 246.05 µg/mL*h) were monitored following 10 and 20 mg/kg IM injection. The withdrawal time of TT from muscle (water temperature, 22 °C) was 9.84 days, rounded up to 10 days (220 degree days). Large C_max/MIC₉₀, AUC_0-inf/MIC₉₀, and T > MIC₉₀ values were obtained for Streptococcus isolates and these PK/PD indices satisfied the criteria required for efficacy evaluation. This study lays a foundation for the optimal use of TT and provides valuable information for establishing therapeutic regimens.

Although enrofloxacin (ENR) is an important pharmaceutical in aquaculture for its excellent efficacy, it is mostly utilized through an off‐label prescription system. Thus, the optimal clinical use regimen is not well‐established. A series of studies was performed to obtain pharmacological and safety data needed for the use of ENR, a synthetic fluoroquinolone, in treating bacterial diseases occurring in black rockfish, Sebastes schlegelii. Minimal inhibitory concentrations showed that ENR exerts a potent in vitro efficacy inhibiting the growth of several pathogenic bacteria at concentrations less than 1 mg/L. ENR with oral doses of 5 mg/kg and up for 1 week significantly prevented mortality of black rockfish infected with Streptococcus iniae and Aeromonas salmonicida, demonstrating in vivo efficacy. Complete protection was obtained against these two bacteria by 10 mg/kg ENR in this in vivo infection trial. Black rockfish did not exhibit any severe abnormal signs by ENR up to 20 mg/kg when assessed by basic haematoclinical and histopathological parameters. Efficacy and toxicity study results collectively suggest that oral dose of 10 mg/kg ENR is optimal to treat bacterial infections. Through muscle residue analyses, the required withdrawal period for safe fish consumption was found to be approximately 90 days by measuring clearance of ENR and its metabolite ciprofloxacin (CIP). This study provides necessary information for the use of ENR to treat two frequently‐occurring bacterial infections, Streptococcus iniae and Aeromonas salmonicida in black rockfish. Obtained data can be the basis for an official guideline for aquacultural ENR use.

Parasitic infections pose significant challenges in aquaculture, and the increasing resistance to conventional anthelmintics necessitates the exploration of alternative treatments. Levamisole hydrochloride (HCl) has demonstrated efficacy against monogenean infections in various fish species; however, research focused on Microcotyle sebastis infections in Korean rockfish (Sebastes schlegelii) remains limited. Therefore, this study aimed to evaluate the efficacy of levamisole HCl against M. sebastis infections in Korean rockfish with the goal of optimizing anthelmintic usage in aquaculture. In this study, we first assessed the susceptibility of M. sebastis to levamisole HCl in vitro. Subsequently, in vivo evaluations were conducted to assess the drug’s efficacy, safety, and to identify optimal administration methods. In vitro experiments revealed concentration-dependent sensitivity of M. sebastis to levamisole HCl, with a minimum effective concentration (MEC) of 100 mg/L. In vivo experiments employed oral administration, intraperitoneal injection, and immersion treatments based on the MEC. Oral administration proved to be a safe method, yielding efficacy rates of 27.3% and 41.6% for 100 mg/kg and 200 mg/kg doses, respectively, in contrast to the immersion and injection methods, which induced symptoms of abnormal swimming, vomiting, and death. Biochemical analyses conducted to assess the safety of levamisole HCl revealed a transient, statistically significant elevation in the levels of glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) on day three post-administration at 20 °C. Following this, no substantial differences were observed. However, at 13 °C, the enzyme levels remained relatively consistent, emphasizing the role of water temperature conditions in influencing the action of levamisole HCl. Our research findings substantiate the efficacy of levamisole HCl against M. sebastis in Korean rockfish, underscoring its potential for safe oral administration. These results provide valuable insights for developing parasite control strategies involving levamisole HCl in Korean rockfish populations while minimizing adverse impacts on fish health and the environment. However, this study bears limitations due to its controlled setting and narrow focus. Future research should expand on these findings by testing levamisole HCl in diverse environments, exploring different administration protocols, and examining wider temperature ranges.

Background: Amoxicillin (AMOX) is widely used in aquaculture for bacterial infections due to its efficacy and safety. Despite official approval for select species, off-label use is common. This study evaluated the antibacterial efficacy and residue depletion of AMOX in five aquaculture species: olive flounder (Paralichthys olivaceus), rainbow trout (Oncorhynchus mykiss), Japanese eel (Anguilla japonica), black rockfish (Sebastes schlegelii), and Israeli carp (Cyprinus carpio). Methods: Fish were administered AMOX orally at 40 mg/kg and 80 mg/kg for seven days. Antibacterial efficacy was assessed by bacterial load reduction and survival rates following artificial infection. Residue depletion was analyzed using HPLC–MS/MS to determine the time required for AMOX levels to fall below the maximum residue limit (MRL, 0.05 mg/kg). Results: AMOX, at 40 mg/kg, significantly reduced bacterial loads in olive flounder, rainbow trout, and Japanese eel (p < 0.05), while Israeli carp exhibited a limited response (p = 0.54). Black rockfish showed moderate efficacy (RPS 72.7%) but increased mortality at 80 mg/kg. Residue levels fell below the MRL within 10 days for all species except Israeli carp (~30 days). Conclusions: These findings highlight species-specific differences in AMOX efficacy and residue depletion rates, emphasizing the necessity of tailored dosing regimens and withdrawal periods to ensure optimal therapeutic outcomes and food safety compliance in aquaculture. Further pharmacokinetic studies are needed to refine dosing strategies, particularly for species with extended residue retention and potential dose-dependent adverse effects.