Scale of Concern: Efficacy of Commercially Available Topical Carp Care Formulations for Recreational Application in Carp

Opportunistic bacterial and fungal infections from surface wounds remain a persistent threat to aquaculture, resulting in significant economic losses and reduced stock welfare. Topical wound sealants are widely employed in recreational aquaculture applications, yet no market regulation or efficacy data exist to support their usage. The broader biological/environmental impacts of these products also remain poorly characterized. This study provides the first quantitative assessment of the antibacterial, antifungal and cellular toxicity of a panel of commercially available topical ‘carp care’ formulations. Our data highlights highly variable to no functional growth inhibition or killing of microbial pathogens, significant inherent cyprinid cellular toxicity, and lack of submerged wet adhesion in all products tested. We show for the first time that commercial propolis solutions are ineffective against the four main pathogenic microorganisms affecting carp. Propolis formulations were also found to induce apoptosis and ROS generation in cyprinid cells in vitro, and permeabilise intact carp skin, questioning the foundation of propolis formulations in topical wound-care treatments for carp rearing/angling. We show improved efficacies can be attained through natural compound implementation, with increased antibacterial and antifungal effects, inherent regenerative benefits to cyprinid fibroblasts, and improved human and environmental safety profiles. This research demonstrates the widespread lack of efficacy in currently commercially available wound sealants for carp; of those tested here, many popular formulations are in fact inherently toxic to carp cells, and also have a permeabilizing effect on intact carp skin due to carrier solvent effects, providing a route for secondary infection; most show no activity against any common carp pathogens; and all uniformly lacked wet adhesion. This work provides a framework standard for the future development of topical wound-care formulations for carp and highlights the need for better dialogue between trade and academia when designing novel wound-care products.