Public aquariums: make quarantine a decision system

In a public aquarium, quarantine is not a waiting room before exhibit. It is a decision unit designed to lower the probability of introducing infectious agents into an established collection. Its value depends less on one fixed number of days than on genuine flow separation, daily observation, risk-based diagnostics and written release criteria.

A 2011 survey sent questionnaires to 60 mainly North American zoos and aquariums and received 42 responses. Among respondents, 95% used a minimum quarantine of at least 30 days and all relied on regular visual examinations. This describes common practice; it does not prove that 30 days is sufficient for every host and pathogen. Duration must reflect origin, water temperature, agent life cycles and test performance.

Separate water, equipment and people

A room that returns quarantine water to permanent collections is not biocontained. Pumps, filters, effluent and overflow routes should be mapped. Splash and aerosols deserve attention, but nets, siphons, buckets, hands, footwear and work surfaces are usually the more obvious routes across the boundary.

Each group needs identifiable, cleanable equipment. Staff should move from lower-risk collections toward new arrivals and avoid reversing that sequence where operations permit. Reusable items are cleaned to remove organic material before a validated disinfectant concentration and contact time are applied.

The FELASA-AALAS recommendations describe quarantine as a high-risk area and emphasise physical isolation, suitable protective equipment and batch-based working. Mixing arrivals or species can restart the epidemiological clock and make it difficult to trace an emerging problem.

Build the health file before arrival

The decision process begins before transport. Teams gather origin, captivity history, recent mortality, treatments, previous examinations and source-water conditions. They identify relevant regulated diseases and priority agents for the species. Missing information is not equivalent to a negative result; it increases uncertainty and may require stronger separation.

At arrival, identification, count, examination and water measurements are recorded. Acclimation should reduce abrupt temperature, salinity or pH changes without physically transferring shipping water into the system. Packaging and effluent need a predetermined route. Early days allow animals to stabilise while structured observation begins.

Observe and sample with a defined question

Daily records cover feeding, swimming, ventilation, space use, colour, visible lesions, faeces and mortality. Every event is linked to tank and date. Without that resolution, an apparently uneventful quarantine may conceal a progressive fall in feed intake or scattered losses.

Testing is risk based. A negative PCR does not certify freedom if too few animals were sampled, the wrong tissue was chosen or shedding is intermittent. Parasitology, culture, histology and necropsy answer different questions. The plan states which animals to sample, at what time, from which tissues and under what preservation conditions.

Routine treatments “just in case” may temporarily suppress some parasites while delaying signs, disturbing microbial communities or selecting resistance. Each intervention needs an objective, veterinary prescribing where required and a response measure. A clinically important event may justify restarting an observation period after treatment ends.

Species-specific husbandry remains essential throughout this process. A quarantine tank that is easy to disinfect but produces chronic crowding, territorial conflict or unsuitable shelter can generate stress-related signs and undermine immunity. Environmental needs, safe visual barriers and feeding strategy should be planned without creating porous furnishings that cannot be cleaned. Elasmobranchs, large pelagic fish and delicate reef species may require different layouts and observation approaches; one room protocol cannot replace a risk assessment for each incoming group.

Release on converging evidence

Time is one criterion, not the verdict. A defensible release combines completion of a minimum period, successful acclimation, no unexplained mortality, stable feeding, normal observations over a defined interval and interpretable targeted results. Designated staff sign the decision with veterinary input proportionate to risk.

The destination matters. Moving apparently healthy fish into a collection of rare, old or vulnerable animals has a different consequence from transfer into an easily isolated unit. The first days after transfer remain part of surveillance, and a handover record should prevent key information from staying behind in the quarantine room.

A failed release decision does not always mean treatment. Options include extended observation, a better-timed sample, separation of a subgroup or cancellation of the introduction. These routes should be agreed before pressure on tank space dictates the outcome.

The release file should retain source documentation, daily observations, laboratory reports, treatments, adverse events and the final rationale. Keeping raw reports rather than only a “negative” label allows later review if disease appears in the receiving collection. It also supports periodic comparison of suppliers and transport routes without assuming that association proves the origin of an infection.

Audit the system, not only the animals

After each batch, the team reviews shared equipment, filtration faults, late results, incomplete treatment and missing records. An all-in/all-out approach allows cleaning, disinfection and, where appropriate, drying between groups. Biofilters require a restart strategy compatible with water quality and the welfare of the next arrivals.

Conclusion

Effective quarantine converts uncertainty into a documented decision. It combines infrastructure, disciplined flows, clinical observation, laboratory evidence and proportionate release criteria. Thirty days may be a useful practice benchmark for many fish, but it is never a universal guarantee.

Vetofish can audit quarantine pathways, design observation and release records, build species-specific testing plans and train teams to maintain a practical health boundary.