Informal Treatment Practices in Ornamental Aquaria: An Overlooked Interface Between Aquatic Animal Health, Antimicrobial Stewardship, and One Health.

Ornamental aquarium keeping collectively involves millions of freshwater, marine, and reef systems in which fish, corals, invertebrates, biofilters, microbial communities, and human husbandry practices are closely interconnected. In these domestic aquatic animal systems, preventive and curative treatments may include antimicrobials, antiparasitics, antiseptics, oxidizing agents, copper-based products, dips, and commercial formulations targeting microbial proliferations or visible system deterioration. Many interventions occur without veterinary diagnosis, microbiological confirmation, standardized dosing, active-ingredient transparency, or post-treatment monitoring. This raises concerns for aquatic animal health and welfare, as whole-system treatments may affect not only the intended pathogen or pest but also non-target organisms, biofilter communities, animal-associated microbiota, and water quality stability. Digital communities and online platforms can rapidly circulate empirical treatment protocols, although they may also provide opportunities for stewardship education and improved husbandry guidance. Current evidence does not support interpreting ornamental aquaria as major independent drivers of antimicrobial resistance. The more defensible concern is stewardship: biologically active compounds may be used repeatedly and empirically in animal systems without diagnosis, professional guidance, or systematic monitoring. This Perspective argues that ornamental aquaria should be recognized as an overlooked interface between aquatic animal health, welfare, antimicrobial stewardship, and One Health. It proposes a research and communication agenda focused on treatment transparency, diagnosis, prevention, biofilter protection, and responsible care practices.