Aquarium corals: documenting lesions before diagnosis

A white area on a coral can represent loss of pigmentation, loss of living tissue or damage to the skeleton. In a public aquarium, assigning a disease name too early may steer an entire response towards the wrong explanation. Resources from NOAA’s Coral Disease and Health Consortium offer a more useful starting point: describe the lesion, document change and collect samples that can answer a defined question. Applying this field-based approach to a captive collection requires particular attention to shared water systems and recent husbandry events.

Separate appearance from explanation

The NOAA terminology distinguishes colour change, tissue loss, skeletal damage and growth anomalies. These are descriptions, not necessarily infectious diagnoses. Their immediate purpose is to let different observers recognise and record the same feature. A partly white colony therefore needs closer inspection to establish whether living tissue remains over the affected area.

For stony corals, exposed skeleton and depigmented tissue should not be recorded as though they were identical. Strongly coloured aquarium lighting can further complicate the interpretation of photographs. A close visual examination adds information that may be missing from a general tank image.

A useful first entry identifies the colony, its taxonomic identification where reliable, the location of the change and the condition of the tissue. Uncertainty should remain visible in the record. Choosing a precise-looking species or disease name from a superficial resemblance can make subsequent comparisons less reliable, rather than more informative.

Turn photographs into comparable observations

The NOAA framework records lesion location, distribution, dimensions and margins. Changes may be focal, multifocal or diffuse, with a distinct or indistinct boundary. Such terms do not explain causation, but they allow a team to recognise progression and choose areas for closer investigation.

For aquarium collections, we suggest keeping three complementary views: the tank context, the whole colony and the lesion detail. Repeat views should use comparable distance, orientation and lighting, with a suitable size reference where practical. Original images should retain their dates and remain available alongside any annotated copies.

The field manual recommends photography both before and after biopsy. This makes the sampling wound distinguishable from subsequent disease progression. In a small colony, an undocumented biopsy site could otherwise be counted as a newly expanding lesion during the next inspection. Recording the intervention is therefore part of monitoring, not merely an administrative addition.

Include apparently unaffected colonies

An investigation should describe which colonies are affected and which show no visible signs. The manual differentiates normal-looking tissue within a diseased colony, apparently healthy colonies in an affected area and reference colonies from an area without observed disease. These are different comparisons and should retain separate identities in the sample record.

The water-system diagram adds another layer in captivity. Separate display tanks may share filtration and water, while neighbouring colonies may experience different local flow or illumination. Any statement about the frequency of lesions should include the number of colonies inspected and explain how they were selected.

Recent events are also worth recording: arrivals, colony movements, maintenance, lighting changes, temperature excursions and circulation failures. An event preceding a lesion is a possible lead rather than proof of cause. A contemporaneous timeline is more useful than a retrospective list containing only the changes that fit the team’s preferred explanation.

Agree on the laboratory question before sampling

Histopathology describes the tissue response and its organisation. Molecular or microbiological analyses address other questions and may require different preservation conditions. The veterinarian and receiving laboratory should agree on sampling locations, containers, fixatives where appropriate and delivery arrangements before tissue is removed.

The interface between affected and apparently unaffected tissue may contain information that a completely denuded area cannot provide. NOAA emphasises sample quality, labelling and the link between collection sites and photographic documentation. This does not mean that every colony requires a biopsy. Sampling should be proportionate to the question and the potential effect on the animal.

Each result needs to remain connected to a particular colony and sample type. Finding an organism in tank water is not equivalent to demonstrating it within a progressing lesion. Likewise, a positive test from normal-looking tissue does not by itself establish that the organism caused the observed damage. Interpretation depends on the combined clinical, pathological and environmental evidence.

Review containment at the system level

During the investigation, biosecurity should address dedicated equipment, staff workflow and the destination of water used for handling. Moving a colony to another tank does not necessarily provide isolation. Water connections and shared tools need to be checked before describing the receiving unit as a quarantine system.

Equipment disinfection is a controlled procedure outside the occupied display, not an instruction to add disinfectant to the collection. The field manual provides an organisational framework, but the practical method must be compatible with the material, animals and facilities involved. Procedures should also prevent contamination of diagnostic samples.

If treatment is considered, the intended outcome and the reassessment criteria should be defined beforehand. Changing several environmental conditions, moving colonies and treating the entire circuit at once makes it difficult to identify why the situation changed. Combined action may be necessary in an urgent case; when it is, a detailed chronology becomes especially valuable.

Know what this approach can establish

Structured observation preserves the evidence needed for a proportionate response. It can improve communication, reveal progression and make laboratory submissions more interpretable. It cannot turn a visual syndrome into a confirmed cause, nor can a field guide establish the effectiveness of a treatment across every species maintained in captivity.

NOAA’s methods were developed for coral disease investigations in reef environments. Their adaptation here concerns documentation, comparison and sample integrity. It should be assessed against the collection’s species, water connections and veterinary objectives, rather than treated as a universal aquarium protocol.

Vetofish can help develop a lesion record, coordinate laboratory sampling and review the sanitary connections within the facility. The practical aim is a usable clinical case file that supports decisions and follow-up, with uncertainty retained wherever the evidence remains incomplete.