Top-coating strategy for tiamulin incorporation into medicated fish feed

Aquaculture plays a critical role in ensuring global food security, especially in the context of rapid population growth. However, the intensification of fish production increases the risk of infectious diseases, leading to the frequent use of antimicrobials. In Brazil, only two antimicrobial drugs are approved for use in aquaculture species, florfenicol and oxytetracycline, which raises concerns about antimicrobial resistance and its consequences for animal, human, and environmental health under the One Health concept. Tiamulin (TIA), a pleuromutilin antimicrobial with known efficacy against Gram-positive and some Gram-negative bacteria, represents a promising alternative for use in aquaculture. This study aimed to develop efficient strategies for incorporating TIA into fish feed, ensuring therapeutic effectiveness while minimising environmental impact. Three top-coating materials were evaluated: ethyl cellulose (EC), gelatine, and vegetable oil. EC proved to be the most effective, promoting homogeneous TIA distribution (RSD < 10%), high incorporation efficiency (>97%), and minimal leaching (<1%) into the water. To support this development, an LC-MS/MS method was developed for the quantification of TIA in feed. The TIA extraction procedure was optimised through design of experiments, and the method was validated, showing selectivity, linearity (<i>r</i> > 0.99), precision (RSD < 2.0%), and accuracy (recovery > 100%). This study highlights the potential of EC as a coating agent for medicated fish feed, aligning with One Health principles by promoting effective treatment while mitigating environmental contamination and resistance dissemination.