Processing of wild-caught fish alive when landed

Most commercially-caught wild fish, that are alive when landed, die either from being left to suffocate in air, or by a combination of suffocation and evisceration. Removing fish from water is highly stressful to them and, in most cases, violent escape attempts are made. Evisceration i.e. disembowelment or gutting, is done without prior stunning. Evisceration methods vary with species. Gibbing is a form used on herring in which the gills, long gut and stomach are removed from a fish by inserting a knife at the gills. The term vivisection, meaning literally dissecting a live animal, would not be inappropriate.

The time taken to die will depend on the species, treatment, and also on the temperature. In a Dutch study, the time taken for fish to become insensible was measured for fish subjected to gutting and to asphyxiation without gutting. This was done for several species of fish (herring, cod, whiting, sole, dab and plaice). It was found that a considerable time elapsed before the fish became insensible as follows:

• gutting alive (gibbing in the case of herring): 25-65 minutes;
• asphyxiation without gutting: 55-250 minutes

Some species adapted to spending periods of time out of water, such as eels, can survive for a very long time when removed from water. There is anecdotal evidence of flatfish landed by a trawl surviving ten hours out of water (see a firsthand account of a trawl).

Sometimes fish are put onto ice as they suffocate, or into iced water. This is likely to result in rapid chilling. It is sometimes believed that cold-blooded animals become less sentient as they cool due to slowed nervous metabolism. However, the process of chilling has been shown to be stressful to fish and may cause violent escape behaviour. Rapidly chilling live fish, therefore, is not humane and it seems likely that putting wild-caught fish onto ice, as they suffocate, will increase the severity of their distress. This practice may also cause them to suffer for longer.

Introducing humane slaughter for wild-caught fish

There are two traditional methods for killing fish that have the potential to be humane, namely percussive stunning and spiking. These methods kill fish individually, and so may not be practical for larger fishing operations with large numbers of smaller fish. For these cases, methods of en mass humane slaughter need to be developed.

Percussive stunning involves a blow to the head with a club or “priest”. This must be performed accurately and with sufficient force to be humane. Automatic percussive stunning devices have been developed for some species in fish farming. These are more reliably accurate than manual stunning. To ensure that percussive stunning does kill humanely, it should be followed immediately by bleeding. However, percussive stunning is not suitable for all types of fish. In spiking (also called “ike jime”) a fish is killed by inserting a spike into the brain. If this is done accurately, the fish can become unconscious immediately.

The video below shows the use of automatic percussive stunners by the company Wild Salmon Direct. This is reportedly the only wild salmon producer using humane slaughter technology. The fish are humanely stunned by a blow to the head, without removing them from the water. They are then “bled” (a cut is made in the area of the heart) which should ensure death occurs while they remain stunned and unconscious. Notice that 1 or 2 individuals show movement and appear to have “come round” after bleeding (1.55, 4.05, 4.55 and 5.05 seconds in). This system would be improved with a manual backup i.e. a worker to manually stun any fish showing signs of recovery. This system would appear to be1, however, a huge improvement over normal practice in commercial fishing where fish are not stunned but are left to die from suffocation in air, or gutted, bled or chilled while still alive.

Electrical stunning systems have been developed for en mass humane slaughter for fresh-water species in fish farming. As with some automated percussive stunning systems, the fish are killed without taking them out of water. A current is passed though the water containing the fish. The fish are stunned immediately, and die without regaining consciousness, if the parameters of the current are sufficient. These will depend on the species and the conductivity of the water. Electrical stunning must be done properly or the fish may be paralysed but still sensible to suffering.

Electrical stunning technology needs to be adapted for use on fishing vessels. An important step in this will be the development of electrical stunning systems for salt water farmed fish species. This is technically more challenging than for fresh water species, due to the greater conductivity of salt water.

Other methods of the humane slaughter of farmed fish may also present the possibility of being adapted for use in some commercial fishing.

For fish killed by suffocation in air, the practice of gutting them while they are still alive is likely to increase the severity of suffering, even though it may reduce the duration. The process of chilling live fish as they suffocate is also likely to increase the severity of suffering and may also increase its duration. Until wild fish are killed humanely they should, at least, not be gutted or immersed in ice-slurry while they are still alive and conscious.

Humane slaughter of crustaceans is discussed at: welfare during killing of crabs, lobsters and crayfish and electrical stunning of crustaceans.

1. Note that has not carried out any welfare assessment regarding Wild Salmon Direct – we simply report the statements and video on their website that state they are using humane slaughter technology.