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Humane electric stunning of farmed sea fish - LK0663

About 15 species of fin fish are farmed in the UK or for the UK market. It is difficult to kill many of these species in a way which meets today’s requirements for welfare standards, carcass quality and processing speeds. As a consequence of this, welfare standards at slaughter have often been poor. For example around 250 million sea bass and bream are killed in Europe each year using slush ice, a practice that FAWC recommended should be prohibited by legislation. To improve fish welfare at harvest we must identify a commercially acceptable means of achieving it, demonstrate its use on UK farms, and allow the industry to propagate this good practice more widely.

Progress has been made elsewhere with mechanical stunning systems suitable for salmon. The resulting pneumatic systems - the MT4, MT5 and Si5 - have been acclaimed for their welfare benefits and are being adopted in the salmon industry. It is expected that this equipment will also be suitable for use with farmed cod and sea trout. Marine Harvest recently attempted to use this approach for halibut but found it unworkable. Mechanical systems are unsuitable for small fish of low individual value due to the low operating speed. Such species include bass, bream, tilapia and portion size trout. Mechanical systems are also unsuitable for flat fish such as turbot and halibut due to fish morphology.

In Defra LINK Aquaculture project TRT07, Silsoe Research Institute and Bristol University together with industry partners developed a commercially acceptable approach to the humane killing of trout using in-water electric stunning. High standards of welfare were achieved and carcass quality standards equal or exceed those of the traditional killing methods. Commercial equipment, based on this research, has been available since December 2003 from Ace-Aquatec ( Four units have been installed, seven units are on order and negotiations are underway for a further 8. An open day demonstrating this equipment has been organized by the HSA for 27th May 2004. The Ace-Aquatec equipment is capable of working at speeds of 20 - 40,000 fish per hour and uses a two stage electric stun/kill without bleeding. Since electric stunning in water requires no targeting or physical contact with the fish, its operation is less subject to human error than most other systems, it is able to work at the high rates required for small fish of low individual value. It should also be suitable for fish with a difficult morphology such as flat fish. It is not practical to use the Ace-Aquatec approach directly in sea water since the high electrical conductivity of the water would make the equipment prohibitively expensive to build. If practical humane electrical stunning systems are to be developed for sea water a wider understanding of interactions between the fish and the electric field is needed, and novel approaches to the application of the stun and the maintenance of insensibility need to be developed.

A physics based model of the electric field around fish has been built and validated for trout in fresh water (conductivity 50–1000 µS/cm) (Lines and Kestin 2004), but the model has not been extended to sea water (~50000 µS/cm), to fish of different morphologies or to situations where electrodes are in contact with the fish. A two-stage stun approach has been developed and implemented in the Ace-Aquatec equipment which results in a power reduction of over 80%. However further significant power savings are needed to make stunning in sea water a practical proposition. Concerns remain that the techniques for predicting and controlling carcass damage caused by the stimulation of the electric field are empirical and rudimentary. The other key researchers interested in electrical stunning of farmed fish are Van der Vis (The Netherlands) and Roth (Norway). Neither has made any significant progress in these key areas largely because their teams lack the appropriate physics and engineering skills. The electric fishing literature also makes very little contribution to this area.

A feasibility LINK project is needed to start this development. The marine fin fish farming industry is relatively new and currently uses wild fish killing practices by default. While growers recognise that welfare issues need to be addressed, other problems of fish culture and farm siting are considered more immediate. A demonstration that fish in sea water can be killed by electric stunning in a commercially acceptable way will encourage and support this emerging industry. This aim will be best met by focusing the project on just one species, and preferably one farmed in the UK.

Most sea water fish farms in the UK grow salmon with some also growing sea trout. Pressure to diversify out of the salmonids is resulting in widespread interest in the marine species that thrive in cold water; however rapid diversification is currently restricted by a shortage of investment capital. Marine species currently available for diversification are cod and halibut. The UK farmed cod harvest is currently 200t/yr, and is expected to rise to over 10 000 t/yr in the next ten years. In the UK, Halibut is farmed by Marine Harvest - who expect to complete their relocation of production to Norway by 2007, by Kames Fish Farms who currently harvest about 50 t/year, and by Crø Lax, who are expecting to harvest 50t/y from 2005. It is likely that other organisations will soon be farming this species. Other species which may soon be farmed commercially include Haddock, Lemon Sole, Plaice, Monk fish and Wolf fish. Turbot and Sea Bass are farmed in limited numbers in the UK using warm, sea water recirculation systems.

This proposal focuses on halibut and aims to identify an electric stun/kill approach suitable for this species. Halibut has been chosen because it is an important, new and expanding species, for which satisfactory killing arrangements do not yet exist. The industry has found it difficult to stun these fish using either automatic or manual mechanical percussion. From a scientific point of view, halibut is of interest because it differs so significantly from portion size trout in size, morphology, physiology, individual value and in the conductivity of the water it lives in. Because of these differences, it is likely that a suitable approach to stunning halibut will be an individually applied, short duration, head only electric stun applied in sea water or on a harvest table, followed by bleeding. This work will therefore significantly extend the understanding of the process of humane killing by electric stunning. The feasibility study will aim to demonstrate humane halibut killing on a farm using laboratory equipment, and to show that this can be done safely, quickly and without impairing carcass quality.

A related proposal has been made to the EC CRAFT scheme. It is entitled ”Development of prototype equipment for humane slaughter of fish in industry” and is led by RIVO (The Netherlands). The proposal deals with two fresh water and two salt water species (eel, tilapia, bass and turbot) and places significant emphasis on fish quality. It does not replicate the work proposed in this LINK proposal, however the synergy between the two will clearly contribute to the wider scientific understanding of this area, will benefit the welfare of farmed fish and help the UK industry to maintain its leading position in this field.
1. An extended understanding of electric stunning of fish
This project will extend understanding of electric stunning to short application times, head only application and application in sea water. The large differences in water conductivity will challenge and extend the mathematical model developed for trout. This work will facilitate the development of a model based methodology enabling targeted experiments to be used for refining the electric stunning parameters for other fish species.
The experimental data is a secure outcome and directly applicable to halibut. It is not known whether the complexity of the model required to interpret the electric field in and around a fish in sea water and to facilitate further generalization will exceed that which is useful, reasonable or affordable.

2. An extended understanding of the quality implications of electric stunning.
The quality metric developed for trout needs to be generalized, and assessments made according to this metric of present and proposed killing methods.
Identification of a relevant quality metric is a secure outcome. However due to the low levels of damage likely to occur and the high value of individual fish, we may not, in this project, be able to attach a high statistical significance to carcass quality comparisons.

3. A demonstration of the humane stun/kill of halibut.
A demonstration will take place on a halibut farm, using the selected approach. This will use laboratory equipment, not suitable, or optimized for routine use. The project partners and other interested parties will be able to view this approach and assess its implications for fish welfare, for equipment design, and the time and cost implications for on farm use.
It is very likely that a demonstrable humane killing system can be identified. However the challenge is to identify an approach which is attractive and motivating to the industry. Problems in achieving this objective might be encountered if inadequate numbers of fish are available because of disease, commercial problems, or high levels of carcass damage.

Project Documents
• Executive Summary : Humane electric stunning of farmed sea-fish   (138k)
Time-Scale and Cost
From: 2005

To: 2006

Cost: £121,072
Contractor / Funded Organisations
Humane Slaughter Association, The, Silsoe Research Institute (BBSRC), Shetland Halibut Company, The, Ace Aquatec, Co-operative Group (CWS) Ltd, Waitrose Ltd, University - Bristol, Silsoe Livestock Systems Ltd, Kames Fish Farming Ltd
Animal Welfare              
Fish Farming