Aquariums need treatment decisions, not guesswork

When a fish develops spots, abnormal swimming or a lesion, adding a broad “general cure” to the water can feel like the fastest response. A scientific perspective published in July 2026 places that act inside a larger system: treatment reaches the animals, non-target organisms, biological filtration and microbial communities at the same time. Its argument is not that every treatment is wrong, nor that aquariums are proven major drivers of antimicrobial resistance. It is that empirical treatment should give way to a traceable decision based on observation, diagnosis, disclosed ingredients and follow-up.

A perspective, not a prevalence survey

Marco Dettori defines informal treatment practices as interventions selected without formal veterinary or microbiological diagnosis, often through product labels, retail advice, forums, social media or shared experience. The paper is a peer-reviewed Perspective. It brings existing evidence together and proposes a research agenda; it does not quantify how often hobbyists, retailers or institutions treat in this way.

That boundary matters. The paper mainly concerns domestic ornamental aquariums, retail systems and their supply chains. Public aquariums generally have different staff, procedures and infrastructure. They nevertheless share the same biological principle: a drug or biocide dispersed through water does not reach only the suspected agent. For institutional teams, the paper offers a decision framework rather than a statistic about their practice.

The interventions discussed include antibacterials, antiparasitics, antiseptics, oxidising agents, copper products, dips and remedies aimed at visible blooms. Some respond to clinical disease; others are used during quarantine, after transport or when a system deteriorates without a clear cause. Similar signs can arise from different disorders, so diagnosis remains the critical step before substance selection.

The aquarium is also a microbial ecosystem

A stable aquarium is not sterile. Its biofilter, media, substrate, pipework and surfaces support a microbiome that processes waste. Nitrification helps convert ammonia and nitrite. A whole-system treatment exposes these communities together with fish, corals, invertebrates and plants.

A 2025 metagenomic study illustrates that complexity in one external freshwater aquarium filter. Researchers reconstructed 203 microbial genomes and identified a nitrifying community dominated by comammox Nitrospira and ammonia-oxidising archaea alongside diverse heterotrophs. The work examined one system and tested no medication. It cannot predict the effect of any product, but it does show why protecting “beneficial bacteria” is more complicated than preserving one bottled strain.

Biofilter composition and activity also respond to oxygen, pH, temperature, flow, organic loading and feeding. Visible improvement after a treatment may therefore leave an underlying cause untouched: overfeeding, an immature filter, repeated introductions, unsuitable stocking or inadequate circulation. If those drivers are not monitored, recurrence can normalise another treatment cycle.

What antibiotic studies actually show

The evidence is more direct for antibiotics. Au-Yeung and colleagues screened twenty compounds in carriage water originating from ornamental-fish tanks at ten Hong Kong shops, sampled monthly for three months. Measured oxytetracycline concentrations ranged widely, from 44.3 to 2,262,064.2 ng/L, and frequently exceeded the authors’ resistance-selection risk threshold. Tetracyclines, fluoroquinolones and macrolides were detected, and exposure was associated with differences in microbial community composition.

This local study describes neither home aquariums nor public aquariums. It does establish that prophylactic exposure and selection pressure are not merely theoretical within the ornamental pathway. It supports reserving antibiotics for a reasoned indication, with a known active ingredient, dose and duration, rather than treating them as general water correctors.

A UK survey published in 2025 adds a practice-based view. Among 350 mostly UK participants, hobbyists reported buying more natural products, while retailers relied more on synthetic treatments and used both prophylactic and curative approaches. “Natural” does not mean biologically inactive or automatically safe for every species, life stage or biofilter. Because the survey relied on responses rather than direct efficacy or toxicity testing, it describes behaviour; it does not rank products.

Put a decision record ahead of administration

A facility can make treatment reviewable with a short pre-treatment record:

• identify the group, species, actual treated volume and exposed non-target organisms;
• date the onset of signs and record behaviour, appetite, ventilation, mortality and lesions;
• measure relevant baseline parameters, including temperature, oxygen, pH, salinity and ammonia according to the system;
• list the working diagnoses and available tests, then state what remains uncertain;
• record every active ingredient and concentration, the calculated dose, route, duration, contraindications and decision-maker;
• define response, stop and escalation criteria, plus the schedule for animal and water monitoring.

If the exact formulation is unavailable, that uncertainty belongs in the safety assessment rather than the small print. Mixing opaque products makes exposure impossible to reconstruct and complicates interpretation if animals or water quality deteriorate. Records should also describe the destination of treated water, filter media, sediment and mortalities under the rules applying to the site.

Separate care, quarantine and whole-system exposure

The first operational question is not only “which product?” but “must the whole system be exposed?” A properly designed treatment or quarantine unit can sometimes reduce non-target exposure and make dosing more reliable. It is not an automatic answer. Capture and transfer can add stress, an infectious agent may already be circulating, and some species tolerate isolation poorly.

Teams therefore need to compare the expected benefit with handling risk, suspected transmissibility, the ability to separate water circuits and the capacity to monitor the patient. Biosecurity then includes equipment flows, cleaning, disinfection, dedicated tools and prevention of cross-contamination. Medication cannot replace that architecture.

A concise daily discussion can use three headings: what we observe, what we know and what we need to measure before acting. This keeps emergency decisions fast while preventing a non-specific sign from automatically becoming a broad-spectrum treatment.

Conclusion: make every treatment explainable

The 2026 Perspective does not demonstrate that ornamental aquariums independently drive the global antimicrobial-resistance crisis. Its more proportionate warning is that biologically active substances can circulate through biofilm-rich animal systems without diagnosis, transparent composition or standardised monitoring.

The practical response is to make each intervention explainable afterwards: initial signs, diagnostic reasoning, tests, substance, exposure, efficacy criteria and waste handling. Vetofish can support quarantine and treatment procedures, circuit audits, water-quality monitoring and team training while keeping prescriptions and risk assessments specific to the animals, facility and applicable jurisdiction.