Antibacterial treatment of lumpfish (Cyclopterus lumpus) experimentally challenged with Vibrio anguillarum, atypical Aeromonas salmonicida and Pasteurella atlantica

Lumpfish is a novel farmed species used as cleaner fish for the removal of lice from farmed salmon. As often with new, farmed species, there are challenges with bacterial infections. The frequency of prescription of antibiotic agents to lumpfish is increasing, despite the lack of knowledge about appropriate doses, duration of treatment and application protocols for the various antibacterial agents. In the current study, we have tested the effect of medicated feed with florfenicol (FFC), oxolinic acid (OA) and flumequine (FLU) on lumpfish experimentally challenged with Vibrio anguillarum, atypical Aeromonas salmonicida and Pasteurella atlantica. We found that all three antibacterial agents efficiently treated lumpfish with vibriosis using 10 and 20 mg kg^-1  day^-1 of FFC, 25 mg kg^-1  day^-1 of OA and 25 mg kg^-1  day^-1 FLU, whereas only FFC (20 mg kg^-1  day^-1 ) had good effect on lumpfish with pasteurellosis. None of the antibacterial agents were efficient to treat lumpfish with atypical furunculosis. FFC 20 mg kg^-1  day^-1 showed promising results in the beginning of the experiment, but the mortality increased rapidly 14 days post-medication. Efficient treatment is important for the welfare of lumpfish and for reducing the risk of development of antibiotic-resistant bacteria. To our knowledge, this is the first study to establish protocols for antibacterial treatment of lumpfish.

Pharmacokinetic Data Show That Oxolinic Acid and Flumequine Are Absorbed and Excreted Rapidly From Plasma and Tissues of Lumpfish

This study examined the uptake, tissue distribution and elimination of the antibacterial agents oxolinic acid and flumequine in lumpfish (Cyclopterus lumpus L.) by use of LC-MS/MS following a single oral administration of 25 mg/kg fish given in feed. Lumpfish are increasingly used as cleaner fish for removal of sea lice on commercially farmed salmon. The production of lumpfish is successful, but there are challenges with bacterial infections and the number of antibacterial treatments has increased in recent years. As the lumpfish is a novel species to farming, there is a need for pharmacokinetic data and establishment of protocols for efficient antibacterial treatment. The current study describes the pharmacokinetic properties of oxolinic acid and flumequine in lumpfish. Absorption of oxolinic acid was moderate and was characterized by a calculated peak plasma concentration (C_max) of 2.12 μg/ml after 10.3 h (T_max) and an elimination half-life (t_1/2β) of 21 h. Area under curve (AUC) and AUC from 0 to 24 h (AUC_0−24h) were calculated to be 60.9 and 34.0 h μg/ml, respectively. For flumequine, plasma C_max was found to be 2.77 μg/ml after 7.7 h (T_max) with t_1/2β of 22 h. The area under the curve (AUC) and AUC from 0 to 24 h (AUC₀₋₂₄) were calculated as 104.3 and 50.3 h μg/ml, respectively. Corresponding C_max values in muscle, liver, and head-kidney for oxolinic acid were 4.01, 3.04, and, 4.68 μg/g, respectively and T_max of 11.1, 9.2, and 10.0 h, respectively. For flumequine, C_max values of 4.16, 4.01, and 7.48 μg/g were obtained in muscle, liver, and head kidney, respectively, with corresponding T_max values of 10.2, 10.3, and 6.0 h. Antimicrobial susceptibility values as determined by minimum inhibitory concentration (MIC) analyses against 28 isolates of Aeromonas salmonicida isolated from diseased lumpfish ranged from 0.06 to 15 μg/ml for oxolinic acid and 0.024 to 6.25 μg/ml for flumequine. Bimodal distributions in susceptibility to both oxolinic acid and flumequine were observed. The combination of pharmacokinetic properties and MIC data make possible calculation of efficient treatment doses, which are needed to improve the welfare of lumpfish and minimize development of antibiotic resistant bacteria.