Rays: plan capture, anaesthesia and tagging

Working with a ray is not a matter of applying a protocol developed for a fusiform fish. An international review published in 2025 brings together current knowledge on batoid capture, restraint, anaesthesia, health assessment, tagging and release. Although written primarily for field research teams, it offers public aquariums a useful planning framework: define the purpose, account for species and body shape, minimise handling time, support the entire disc, maintain appropriate branchial irrigation, and agree stopping and recovery criteria before capture begins.

Planning starts before the animal is captured

Rays comprise approximately 630 species spanning very different sizes, habitats and swimming modes. Their flattened bodies, ventral gill slits and enlarged pectoral fins change the practical risks of capture and restraint. A net, tank or examination table suitable for a small skate may be unsafe for a large stingray or a pelagic species.

The review starts with a harm–benefit assessment. Is intervention necessary? Could observation, photography, non-restrained imaging or existing data answer the question? When capture remains justified, the team should define roles, the animal’s route, equipment, target duration, water-quality requirements, management of any defensive spine and clear abort criteria.

This preparation prevents improvisation beside the exhibit. Transfer and recovery containers must be ready before capture. Their dimensions should reflect disc width, total length and turning ability, not body mass alone. Contact surfaces need to be smooth and wet, without corners that could trap the disc or tail.

Support the disc and protect ventilation

A ray should not be lifted by its tail, gill slits or fin margins. When movement is necessary, a soft support that distributes load beneath the body reduces pressure points and helps protect the mucous layer. Large animals should remain in water whenever the procedure allows. Staff safety needs to be designed into the method without traumatic restraint: identify the spine position, clear the workspace, assign enough trained personnel and communicate every movement.

Unlike several pelagic sharks that depend heavily on forward movement for ventilation, many rays use buccal pumping. This does not make extended air exposure safe. Body position, temperature, branchial irrigation and handling duration all influence physiological burden. Teams should monitor spiracular or gill-slit movements, tone and reflex responses while recording pre-existing injuries.

An empirical study of 61 flapper skates (Dipturus intermedius) caught by rod and reel in Scotland illustrates that burden. The animals generally developed mild metabolic acidosis, which was greater at warmer water temperatures and after longer fight times. Disturbance worsened while skates were handled on deck. These field findings do not define a universal threshold for aquarium collections, but they support three practical refinements: shorten capture, limit heat exposure and minimise time out of water.

Anaesthesia has no one-size-fits-all recipe

Apparent immobility is neither demonstrated anaesthesia nor proof of good welfare. The review discusses local and general anaesthesia while emphasising the limited quantitative evidence available specifically for batoids. Selection depends on species, procedure duration and invasiveness, water temperature and salinity, available equipment, and the team’s ability to monitor induction and recovery.

General anaesthesia may enable a longer or more precise procedure, but it adds induction, monitoring and recovery phases. Local anaesthesia may reduce the need for general immobilisation in selected procedures, yet it does not remove the need for correct restraint or resolve uncertainty about efficacy. Agent selection, dose and depth criteria belong in an individual veterinary protocol and must comply with the relevant legal framework. Published doses cannot safely be copied from one species to another.

Before induction, the team should specify what will be monitored: ventilation, reflexes, heart rate where meaningful, water temperature and oxygenation, elapsed time and recovery quality. A contingency plan should explain how to stop, restore effective irrigation and move the animal to recovery. If a procedure cannot be monitored adequately, it should be simplified or postponed.

A tag must answer a defined question

An acoustic transmitter or other device is justified only when the expected data are useful and cannot be obtained by a less invasive method. Relative tag mass alone does not demonstrate suitability. Batoid body shape, coelomic space, future growth, drag, implantation site and swimming mode all matter.

The review warns that commonly cited tag-burden rules were developed largely for teleosts. Species-specific thresholds for rays remain a major knowledge gap. Aquarium plans should therefore state the objective, follow-up period, attachment method, aseptic steps, wound monitoring, removal criteria and response to changes in behaviour or feeding.

Internal tagging requires aseptic surgery and a competent team. External attachment avoids coelomic implantation, but may increase drag, catch on exhibit structures or alter disc movement. The best device is not the one producing the most data; it is the one that answers the question with the lowest defensible burden and a follow-up plan the facility can deliver.

Measure recovery instead of assuming it

After the procedure, regular ventilation, appropriate posture and return of reflex responses should be documented. The semi-quantitative health scores and Reflex Action Mortality Predictor assessments discussed in the review combine features such as ventilation, body movement, eye condition and standardised reflexes. They require adaptation and validation for the focal species and setting; a field score does not automatically become a universal clinical endpoint.

Follow-up extends beyond emergence from anaesthesia. It includes space use, feeding, ventilation, colour, skin integrity, wound condition and interactions with tank mates. Any drift should be compared with procedure timing, restraint duration and water records. Acute stress can alter physiology and behaviour, but no single indicator proves cause.

What the evidence can—and cannot—support

The central source is a methods review, not a comparative trial delivering one approved protocol. Evidence is heterogeneous, often field-based, limited to a few species and difficult to transfer directly to a public aquarium. The authors identify major gaps in analgesia, local anaesthesia, physiological indicators, tag burden and long-term effects.

The defensible operational conclusion is therefore disciplined preparation: a species-specific protocol, a dry run without the animal, correctly sized equipment, clear roles, timekeeping, stopping criteria, monitoring and structured debrief. Each intervention can improve the next protocol, but one successful case should not be promoted as a general rule.

How Vetofish can help

Vetofish can help public aquariums prepare interventions on rays through risk assessment, equipment selection, anaesthesia and monitoring protocols, clean workflow design, recovery scoring and team training. The aim is to minimise burden, protect staff and obtain interpretable information without promising a universal method.