Aquatic Animal Health Code
Welfare aspects of stunning and killing of farmed fish for human consumption
These recommendations apply to the stunning and killing of farmed fish species for human consumption.
These recommendations address the need to ensure the welfare of farmed fish, intended for human consumption, during stunning and killing including transport and holding immediately prior to stunning.
This chapter describes general principles that should be applied to ensure the welfare of fish for stunning and killing for human consumption and also applies to farmed fish killed for disease control purposes. Other measures applicable to emergency killing for disease control purposes are addressed in Chapter 7.4.
As a general principle, farmed fish should be stunned before killing, and the stunning method should ensure immediate and irreversible loss of consciousness. If the stunning is not irreversible, fish should be killed before consciousness is recovered.
Persons engaged in the handling, stunning and killing of fish play an important role in their welfare. Personnel handling fish for stunning and killing should be experienced and competent in the handling of fish, and understand their behaviour patterns as well as the underlying principles necessary to carry out their tasks. Some stunning and killing methods may pose a risk to the personnel; therefore training should cover occupational health and safety implications of any methods used.
If fish are to be transported prior to stunning and killing, this should be done in accordance with OIE recommendations on the welfare of farmed fish during transport (see Chapter 7.2.).
Design of holding facilities
The holding facilities should be designed and specifically constructed to hold a certain fish species or group of fish species.
The holding facilities should be of a size that allows holding a certain number of fish for processing in a given timeframe without compromising the welfare of the fish.
Operations should be conducted with minimal injury and stress to the fish.
The following recommendations may help to achieve this:
nets and tanks should be designed and maintained to minimise physical injuries;
water quality should be suitable for the fish species and stocking density;
equipment for transferring fish, including pumps and pipes, should be designed and maintained to minimise injury.
Unloading, transferring and loading
Fish should be unloaded, transferred and loaded under conditions that minimise injury and stress to the fish.
The following points should be considered:
Water quality (e.g. temperature, oxygen and CO2 levels, pH and salinity) should be assessed on arrival of fish prior to their unloading, and corrective action taken if required.
Where possible any injured or moribund fish should be separated and killed humanely.
The crowding periods of fish should be as short and infrequent as possible to avoid stressful conditions arising.
The handling of fish during transfers should be minimised and preferably fish should not be handled out of water. If fish need to be removed from water, this period should be kept as short as possible.
Where feasible, and when applicable, fish should be allowed to swim directly into a stunning device without handling to avoid handling stress.
Equipment used to handle fish, for example nets and dip nets, pumping devices and brailing devices, should be designed, constructed and operated to minimise physical injuries (e.g. pumping height, pressure and speed are important factors to consider).
Fish should not be fasted (deprived of food) before killing for longer than is necessary, e.g. to clear the gut or to reduce undesirable organoleptic properties.
There should be a contingency plan to address emergencies and minimise stress during unloading, transferring and loading fish.
Stunning and killing methods
The choice of method should take account of species-specific information where available.
All handling, stunning and killing equipment should be maintained and operated appropriately; it should be tested on a regular basis to ensure that performance is adequate.
Effective stunning should be verified by the absence of consciousness.
A backup stunning system is necessary. Any fish mis-stunned, or regaining consciousness before death, should be re-stunned as soon as possible.
Stunning should not take place if killing is likely to be delayed such that the fish will recover or partially recover consciousness.
While absence of consciousness may be difficult to recognise, signs of correct stunning include i) loss of body and respiratory movement (loss in opercular activity); ii) loss of visual evoked response (VER); iii) loss of vestibulo-ocular reflex (VOR, eye rolling).
Mechanical stunning and killing methods
Percussive stunning is achieved by a blow of sufficient strength to the head applied above or immediately adjacent to the brain in order to damage the brain. Mechanical stunning may be achieved either manually or using specially developed equipment.
Spiking or coring are irreversible stunning and killing methods of fish based on physical damage to the brain by inserting a spike or core into the brain.
Shooting using a free bullet may be used for killing large fish (such as tuna). The fish may either be crowded in a net and shot in the head from the surface, or individual fish may be killed by shooting in the head from under the water (commonly called lupara).
Unconsciousness following mechanical stunning is generally irreversible if correctly applied. In cases where the loss of consciousness is transient, fish should be killed before consciousness is recovered.
Electrical stunning and killing methods
Electrical stunning involves the application of an electrical current of sufficient strength and duration, and suitable frequency to cause immediate loss of consciousness and insensibility of the fish. The conductivity of fresh and brackish water varies, so it is essential to establish the parameters of the electrical current to ensure proper stunning at the site of stunning.
The electrical stunning device should be constructed and used for the specific fish species and their environment.
Unconsciousness following electrical stunning may be reversible. In such cases fish should be killed before consciousness is recovered.
Fish should be confined beneath the surface of the water, and there should be a uniform distribution of electrical current in the stunning tank or chamber.
In semi-dry electrical stunning systems, fish should enter the device head first to ensure rapid and efficient stunning.
Other killing methods
The following methods are known to be used for killing fish: chilling with ice in holding water, carbon dioxide (CO2) in holding water; chilling with ice and CO2 in holding water; salt or ammonia baths; asphyxiation by removal from water; exsanguination without stunning. However, they have been shown to result in poor fish welfare. Therefore, these methods should not be used if it is feasible to use the methods described in points 2 and 3 of this article, as appropriate to the fish species.
Summary table of some stunning/killing methods for fish and their respective welfare issues
A combination of methods described in the table below may be used.
|Specific method||Key fish welfare concerns/requirements||Advantages||Disadvantages|
|Mechanical||Percussive stunning||The blow should be of sufficient force and delivered above or adjacent to the brain in order to render immediate unconsciousness. Fish should be quickly removed from the water, restrained and given a quick blow to the head, delivered either manually by a club or by automated percussive stunning. The effectiveness of stunning should be checked, and fish be re-stunned if necessary. It can be a stun / kill method.||Immediate loss of consciousness. Suitable for medium to large sized fish.||Hand operated equipment may be hampered by uncontrolled movement of the fish. Mis-stunning may result from a too weak blow. Injuries may occur. Manual percussive stunning is only practicable for the killing of a limited number of fish of a similar size.|
|Spiking or coring||The spike should be aimed on the skull in a position to penetrate the brain of the fish and the impact of the spike should produce immediate unconsciousness. Fish should be quickly removed from the water, restrained and the spike immediately inserted into the brain. It is a stun / kill method.||Immediate loss of consciousness. Suitable for medium to large sized fish. For small tuna, spiking under the water avoids exposure of fish to air. The pineal window of tuna facilitates spiking for this species.||Inaccurate application may cause injuries. Difficult to apply if fish agitated. It is only practicable for the killing of a limited number of fish.|
|Free bullet||The shot should be carefully aimed at the brain. The fish should be positioned correctly and the shooting range should be as short as practicable. It is a stun / kill method.||Immediate loss of consciousness. Suitable for large sized fish (e.g. large tuna).||Shooting distance; calibre need to be adapted. Excessive crowding and noise of guns may cause stress reaction. Contamination of the working area due to release of body fluids may present a biosecurity risk. May be hazardous to operators.|
|Electrical||Electrical stunning||Involves the application of an electrical current of sufficient strength, frequency and duration to cause immediately unconsciousness. It can be a stun / kill method. Equipment should be designed and maintained correctly.||Immediate loss of consciousness. Suitable for small to medium sized fish. Suitable for large numbers of fish, and the fish do not have to be removed from the water.||Difficult to standardise for all species. Optimal control parameters are unknown for some species. May be hazardous to operators.|
|Semi-dry electrical stunning||The head of the fish should enter the system first so electricity is applied to the brain first. Involves the application of an electrical current of sufficient strength, frequency and duration to cause immediately unconsciousness. Equipment should be designed and maintained correctly.||Good visual control of stunning and the ability for re-stunning of individual fish.||Misplacement of the fish may result in improper stunning. Optimal control parameters are unknown for some species. Not suitable for mixed sizes of fish.|
[Note: the terms small, medium and large fish should be interpreted relative to the species in question.]
Examples of stunning/killing methods for fish groups
The following methods enable humane killing for the following fish groups:
percussive stunning: carp, salmonids;
spiking or coring: tuna;
free bullet: tuna;
electrical stunning: carp, eel, salmonids.
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