Trauma linked to fishing nets and accidental catches of swordfish
Trauma linked to fishing nets includes all physical injuries suffered by swordfish when it finds itself trapped, accidentally or deliberately, in fishing gear: gillnet, trawl, longline or seine. It is not a disease in the classic sense of t...
What is it?
Trauma linked to fishing nets includes all physical injuries suffered by swordfish when it finds itself trapped, accidentally or deliberately, in fishing gear: gillnet, trawl, longline or seine.
It is not a disease in the classic sense of the term, but a set of traumatic injuries that can range from simple scratches to serious injuries, sometimes fatal.
Swordfish, a powerful and fast pelagic fish, thrash violently when caught, often worsening the initial damage.
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:
The signs vary depending on the severity and location of the lesions.
We can observe marks or lacerations on the skin, often linear, corresponding to the friction of the mesh of the net.
The rostrum (the swordfish's characteristic sword) may be broken, cracked or eroded, especially if it has been caught in the mesh while struggling.
Torn, crushed or partially severed fins are common, particularly the caudal fin and pectoral fins.
The gills, which are very fragile, can be compressed or injured, causing respiratory difficulty visible through abnormal swimming or irregular opercular movements.
Pallor of the tissues, localized swelling or external hemorrhage indicate deeper lesions.
In severe cases, the animal remains motionless on the surface or sinks, unable to swim normally, a sign of extreme exhaustion or traumatic shock.
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 mechanical contact with fishing gear: net mesh, trawl cables, longline line or hook.
The fish is injured while struggling to free itself, which wears or tears the skin, fins and sometimes the rostrum.
The duration of retention in the gear before returning to the water or death aggravates the intensity of the lesions.
The physiological stress linked to capture (muscle exhaustion, accumulation of lactic acid) also weakens the animal, making it more vulnerable to secondary infections once released.
Areas of intensive fishing with gillnets or pelagic trawls increase the risk of accidental capture.
Prolonged trolling or netting increases the severity of injuries.
Young individuals and fish already weakened (disease, parasitism) tolerate the stress of capture less well.
High water temperature or low dissolved oxygen worsens respiratory exhaustion during net wrestling.
Rough handling when unhooking or re-entering the water also increases the risk of further trauma.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
There is no “diagnosis” in the classic veterinary sense for a wild fish at sea.
The evaluation is done by direct observation of visible lesions: wounds, damaged fins, broken rostrum, abnormal swimming behavior.
In a scientific research, aquarium or rehabilitation pond context, a more in-depth examination can be carried out by a veterinarian specializing in aquatic or exotic species, including observation of the gills, skin and swimming behavior.
Treatment
At sea, no curative treatment is generally possible for swordfish released after accidental capture.
In the exceptional case of an individual kept in a specialized structure (rehabilitation tank, scientific aquarium), treatment may include wound care, local antisepsis, and in certain cases antibiotic treatments for preventive purposes against secondary infections, always under specialized veterinary supervision.
Respiratory support (well-oxygenated water) and stress limitation are essential to recovery.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Prevention is essentially based on responsible fishing practices.
The use of devices that reduce bycatch, regular monitoring of nets to limit immersion time, and gentle and rapid handling of live-caught fish reduce the risk of serious injury.
Training fishermen in good release practices (avoid lifting fish by the rostrum, limiting time out of water, promoting rapid, gentle release) helps reduce delayed mortality.
Appropriate fishing regulations, such as limiting fishing zones or periods in breeding habitats, also contribute to the preservation of the species.
Possible complications
The main complications are secondary wound infections, particularly bacterial or fungal, which can settle on injured tissues.
Severe gill damage can lead to progressive respiratory failure and delayed death after release, even if the fish initially appeared viable.
A broken rostrum can permanently impair the animal's hunting ability, compromising its long-term survival.
Extreme muscle exhaustion can also cause sometimes fatal metabolic shock, including after an apparently successful return to the water.
When to see a veterinarian
Fish observed with deep wounds or significant bleeding after capture
Abnormal swimming, fish sinking or remaining motionless on the surface after release
Visibly broken or deformed rostrum
Marked difficulty breathing (very rapid or irregular opercular movements)
Context of research or rehabilitation basin requiring veterinary advice specialized in aquatic species
Prognosis
The prognosis directly depends on the severity of the injuries and the time spent in the fishing gear.
Superficial injuries with rapid return to water often allow survival and natural healing at sea.
On the other hand, significant gill damage, extreme exhaustion or rostrum fractures significantly worsen the prognosis, with a risk of delayed mortality even after an apparently successful return to the water.
Frequently asked questions
Can a swordfish accidentally caught and released survive?
Yes, it is possible if the injuries are superficial and the return to the water is quick. But severe exhaustion or deep lesions greatly reduce the chances of survival, even if the fish appears to be swimming normally when released.
Does the broken rostrum grow back?
The rostrum is a bony structure that does not regenerate like soft tissue. A fracture may heal partially but often leaves a permanent deformity, which can make it difficult for the animal to hunt.
Why can't we treat a swordfish injured at sea?
Swordfish are wild pelagic fish, impossible to capture and handle without additional risk for treatment at sea. Care is only possible in specialized structures such as certain research centers or large aquariums.
Do these injuries have an impact on the swordfish population?
Incidental captures and resulting delayed mortality are monitored by fisheries management agencies because they can affect wild population dynamics, in addition to targeted fishing.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
WOAH — Organisation mondiale de la santé animale (ex-OIE)
Content reviewed by the TunisieVet editorial team · Updated 18 August 2026
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