other disease Arapaima

Trauma and injuries from fishing nets (accidental bycatch) in arapaima

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Definition Signs Causes Diagnosis Treatment Prevention Complications When to see a vet Prognosis FAQ Sources Affected species

What is it?

Fishing net-related trauma encompasses the physical injuries arapaima sustain when caught accidentally or intentionally in a net, trap, or other fishing gear. This large Amazonian freshwater fish, capable of exceeding two metres in length, breathes partly atmospheric air and must surface regularly. When trapped in a net, it struggles violently, worsening skin lesions, torn fins, and sometimes fractures or asphyxiation. This is a frequent problem in fish farming, commercial fishing, and capture operations for transfer to holding tanks or public aquariums.

Commonly observed signs

These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.

Related signs — each one links to its page:

Non-healing wound Abnormal swimming Damaged fins Swelling Reduction Loss of appetite Pain

The most visible signs are wounds, scrapes, or lacerations on the skin, often on the flanks, head, or near the fins.

Fins may be torn, frayed, or partially ripped away by the mesh.

Local swelling, redness, or discoloured patches indicate inflammation or early infection.

The injured fish often swims abnormally, losing balance or staying near the surface, partly due to stress and increased need to breathe air.

General lethargy, loss of appetite, and more frequent surface breathing reflect significant stress, sometimes associated with early septicaemia if wounds become infected.

In severe cases, extensive scale loss, exposed deep tissue, or even fracture or skeletal deformity may be seen following vigorous escape attempts.

When to consult without delay

This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.

Causes and risk factors

The direct cause is prolonged contact and friction against the mesh, trap, or other capture gear. The animal's struggle to escape intensifies skin and muscle damage.

Partial asphyxiation also plays a role: since arapaima is an obligate air-breather, if trapped underwater unable to surface for air, stress and thrashing increase, worsening injuries.

Once skin is breached, opportunistic bacteria naturally present in the water can colonise the wound and cause secondary infection.

Capture in fine-mesh nets or poorly maintained gear, as well as prolonged handling out of water, increases the risk of severe injury.

High fish density in the net promotes friction between individuals and against the fishing gear.

Large arapaima, being heavier and more powerful, often sustain more severe injuries because their resistance strength is considerable.

Poor water quality, high temperature, or low oxygen levels increase stress and slow wound healing after injury.

Diagnosis and care

Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.

The veterinarian or aquaculture technician performs a visual examination of the extent of wounds, fin tears, and the animal's general condition (swimming, breathing, appetite).

A skin or mucus sample may be collected if secondary bacterial or fungal infection is suspected, to guide treatment.

Observation of behavior in the recovery tank (frequency of surface breaks, posture, activity) helps assess the severity of stress and trauma.

Treatment

Management focuses on keeping the animal in clean, well-oxygenated water to minimize stress and promote natural healing.

Antiseptics suitable for aquatic environments may be applied directly to wounds to limit bacterial colonization.

If infection is confirmed, antibiotic treatment by systemic injection or immersion bath may be prescribed by the veterinarian.

Supportive care, such as adding salt or stress-reducing products to the water, may be recommended depending on the situation.

Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.

Prevention

Using appropriate capture gear with sufficiently large mesh and in good condition reduces injury risk.

Limiting confinement time in the net and rapidly transferring the fish to a recovery tank with well-oxygenated water is essential.

Gentle handling techniques, with body support and avoiding excessive friction, minimise skin injuries.

Regular monitoring of water quality (oxygen, temperature, cleanliness) in recovery tanks promotes better wound healing and limits secondary infections.

Possible complications

Untreated wounds can progress to generalized bacterial infection (sepsis), which may be fatal.

Secondary fungal infections can develop on damaged skin areas, particularly in cold water or poor-quality conditions.

Severe fin damage can permanently impair the animal's swimming ability and balance.

Prolonged stress from trauma can weaken the immune system and increase vulnerability to other diseases.

When to see a veterinarian

The animal has extensive or deep wounds, or wounds showing no improvement after several days.

Fins are severely torn, or the animal has lost balance persistently.

The animal refuses to feed, remains lethargic, or spends an abnormal amount of time at the surface.

Swelling, marked redness, or whitish deposits appear on a wound.

Multiple animals from the same tank or capture show similar signs, suggesting a collective infection risk.

Prognosis

The prognosis is generally favorable for superficial wounds if the animal is promptly placed in good-quality water and monitored.

Deeper lesions, severe fin tears, or fractures carry a more guarded prognosis and may result in lasting functional impairment.

Untreated secondary infection can be fatal, particularly in animals already weakened by capture stress.

Frequently asked questions

Can an arapaima captured in a net heal on its own without treatment?

Small superficial scrapes can heal on their own in clean, well-oxygenated water. However, any deep wound, extensive injury, or one that worsens requires veterinary attention to prevent secondary infection.

Why is the arapaima particularly sensitive to net injuries?

It's a fish that must breathe air at the surface regularly. If it gets trapped and cannot come up, it thrashes violently, which worsens skin injuries and stress, in addition to the risk of suffocation.

How long does it take for a net wound to heal in an arapaima?

This depends on the severity of the injury and water quality. A minor scrape can heal in a few days to a few weeks, while a deep wound may require longer-term follow-up with regular care.

Can you release an injured arapaima directly into the wild?

It is preferable to keep it in a recovery tank until the wound has substantially healed, as a weakened or injured animal is more vulnerable to predators and infections in its natural environment.