Comparison of Common Slaughter Methods for Farmed Finfish


Which Method of Slaughter is Best?

There is a wide variety of slaughter techniques used between and within farmed fish species, as follows:

•  Exposure to air

•  Ice slurry

•  Bleeding

•  Gutting

•  Anaesthesia

•  Carbon dioxide

•  Electrostunning

•  Ike Jime (Spiking)

•  Percussive stunning 

In general, the slaughter methods that are slower result in more movement by the fish and are generally perceived as being more aversive. The only movement seen using the faster methods, (i.e. percussive stunning and spiking) occurs during pre-slaughter handling. While there is a developing consensus that fish feel pain, and respond to this pain with aversive movements, this is not yet accepted by all. However, there is a strong perception of concern from people viewing slaughter operations when they observe fish exhibiting aversive behaviour. The perception of fish retailers reflects this attitude and many have set standards for suppliers that focus on minimizing the potential for fish stress and suffering. In addition, methods that cause stress and aversion also cause quality issues such as reduced shelf-life, flesh gaping, softness, and bloodspotting.


LOW STRESS SLAUGHTER METHODS

Percussive Stunning

Pros

•  Established in literature and aquatic and terrestrial industry for many years as the optimal technique for humane slaughter.

•  The quality benefits have been clearly demonstrated and documented as increased time to rigor (typically 24 hrs standard industry practice for salmon, as opposed to 1-2 hours for other existing slaughter techniques), reduced flesh gaping and softness, improved colour visualisation, reduced bloodspotting and increased shelf-life.

•  Can be simply and manually applied by the use of a club or 'priest'.

•  Substantial progress has been made in the development of commercially viable pneumatic stunning machines over the last 4 years and these are now widely used by the farmed salmonid and yellowtail kingfish industries.

•  Automated technology is available so fish are now able to be directed to machines without manual handling, in water, up to the point of stun, reducing the amount of manual labour required.

Cons

•  A manually applied club generates operator fatigue and can lead to imprecise or insufficiently strong blows.

•  Automated systems require operator training and management for them to remain effective. A maintenance program is required to keep mechanised equipment functioning properly.


Anaesthesia

Pros

•  True anaesthesia (not carbon dioxide) using an anaesthetic like AQUI-S can be non-aversive

•  Low-stress crowding followed by anaesthesia and then a slaughter process such as percussive stunning can lead to improved quality and increased time to rigor

Cons

•  In most cases the anaesthetic used renders the fish unfit for human consumption.

•  Only AQUI-S can be used for anaesthesia of fish destined for food, but this is still not yet permitted in most aquaculture practicing countries.

•  Anaesthetics may leave a detectable flavour taint in the fish flesh

•  Difficult to contain and dispose off and outfall to the environment is not acceptable to some government authorities

•  Can be expensive with ongoing use of anaesthetics


Electrical Stunning

Pros

•  Offers an established humane method of slaughtering fish

Cons

•  Electrical stunning is prone to cause bone fracturing, haemorrhaging, and bloodspotting and therefore there are few commercial operations using this method, particularly for salmonids, which are susceptible to these issues anyway. Also, the use of electricity to stun humanely without damaging the fish requires control, which is often lacking in systems.

•  Has market perception problems with 'electrocution' of fish being humanised in the marketplace as a 'grisly' practice.

•  Safety is an important concern with electricity and water and there is potential for fatal accidents due to malfunction or unsafe work practices.

•  Can be expensive and typically requires 240/250V power.


Ike jime or brain spiking

Pros

•  Brain spiking has been successfully used manually in the tuna and yellowtail industries and provides a rapid slaughter technique with concurrent quality benefits.

 

Cons

•  Spiking of the brain, or ike jime, requires a high level of precision and expertise

•  Significant staff welfare issues are involved with using spikes or knives while manually handling live fish.

•  It is relatively slow and so not practical for large volume harvests which are carried out by most farms now (large labour component).

•  Has not been able to be mechanised due to the difficulty in accurately locating the brain with varying fish size.

•  It is possible that parts of the brain which are not destroyed continue to function after the spiking.

•  Post-mortem muscular twitching can be quite severe and this is a significant market perception issue as fish appear 'alive'.

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