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You are here: HomeRemoval From Water

Removal From Water

The majority of methods for stunning and killing involve removing fish from the water alive and conscious. Stress is inevitable once they are out of their natural environment. Whilst a brief period out of water is often difficult to avoid, fish must not be left in air prior to slaughter for more than 15 seconds. Beyond 15 seconds they will display more pronounced aversive behaviour and become more difficult to handle.

Regardless of the method of stunning and killing, the method for delivering fish to the stunning point should be suitable to provide fish at a similar rate to the stun rate so that they are not exposed to air for longer than necessary. The three most common delivery methods are hand nets, pumps and braille nets. Hand nets are only suitable for small numbers of fish.

To reduce the amount of time fish are exposed to air, they should be removed from water, or dewatered, as close to the stunning point as possible. The dewatering process should be designed to move fish gently and promptly to the stunner in the correct orientation. Out of water, fish are more susceptible to injury and therefore equipment needs to be designed to reduce impact points and the possibility of bruising.

Live fish must not be out of water for longer than 15 seconds

Rested harvest/anaesthetics

In some countries an aquatic anaesthetic, with the active ingredient iso-eugenol, is used to sedate fish prior to their removal from the water. This anaesthetic, which can be used immediately prior to slaughter, is applied in solution to the water. The fish are then introduced into the anaesthetic solution, where they remain for 30 minutes. Once fully sedated, they are removed from the water and then percussively stunned. Alternatively, they remain in the water and are introduced into carbon dioxide saturated water.

This type of harvest is known as ‘rested’ harvesting. ‘Rested’ harvests can have the added advantage of improved flesh colour, firmness and appearance, reduced gaping and a delay in the onset and severity of rigor when compared to conventional harvesting methods. These advantages result from the lower levels of stress experienced by the fish. Anaesthetic concentration, exposure time, water temperature and fish size and weight are factors that need to be carefully considered when using this method. Currently this method is not available in the EU as there are no anaesthetic products licensed for use.


Pumps used to move fish from the crowd pen should be well maintained to avoid damage to the fish. The pump determines the speed and rate at which fish are delivered to the stun point, therefore careful consideration is needed when deciding which pump is most suitable.

Air lift pump

The air lift pump works by bubbling air up into the pipe, lifting the fish and the water with it. The system needs to be set-up in deep water to generate the correct pressure. Fish are supplied in a continuous flow to the stunning point. The efficiency and effectiveness of this pump is dependent on precise set-up and operation and it is therefore important that all manufacturer’s instructions are followed.

Venturi pump

Jets of water cause a rapid flow of fish through the pipe. These pumps are capable of delivering fish in a continuous flow down long pipes. Unlike air pumps they can be used in relatively shallow water and are easier to run, although they tend to be more expensive to buy.

Vacuum pump

These supply fish in batches and are not suitable for pumping fish long distances (over 30 metres). When using these pumps it is difficult to monitor the fish as they cannot be seen.

Dual action pumps

These also work using a vacuum system but involve two pumps working in tandem, resulting in a continuous supply of fish to the stunning point.


Pipes are often used to transport fish from the crowd pen to the stunning point. They should always be as short as possible. The time fish spend in the pipe should be kept to a minimum, and never be more than two minutes. Any delay can have an adverse effect on the fish and increase stress levels. At the end of each harvest, and during any breaks, the pipes must be flushed through to ensure there are no fish left in the pipes. A sponge ball of suitable size can be used to ensure effective flushing of the pipes.


Braille nets must always be used with a lining inside the net. This lining helps keep water within the net and provides some protection to the fish during removal from the crowd pen; it also minimises damage caused by abrasion of the fish against the nets. Brailles should never be overfilled as this will cause excessive pressure on the fish, causing damage or death. The braille must be well maintained and regularly checked for damage. The mesh size must be appropriate for the fish being brailled and there must be no rough edges on the sides or chains which may damage the fish as they are dragged through the crowd pen.

The braille must be moved slowly and lowered to make contact with the unloading table before the fish are released, otherwise fish may be injured on exit.  

Figure 5: Braille net risk areas


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