| Fish Health and Welfare |
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Humane Slaughter - preserving animal welfare and avoiding suffering
As for all animals, aquacultured species have to be treated in order to maintain and preserve their welfare. It is of first interest to avoid any unnecessary handling, use automatic and non-invasive techniques for fish monitoring and maintaining densities in a balanced way, thus allowing maximum growth with minimum disturbance, or unwanted strong hierarchies among the population. As chronic stress may produce medium term immune suppression and energy depletion, a good knowledge of the aquacultured species should provide information for required energetic load for growth that does not produce chronic stress.
Farmed fish and shellfish have to be harvested and prepared for the consumer market. Two important issues for farms in this respect:
- Animal welfare issue - the fish are treated in an appropriate manner; involves avoidance of animal suffering and minimising slaughter time.
- Quality preservation issue - an adequate slaughtering process in order to prevent long-term stress response from the animal.
It is generally considered that the best quality flesh is that which is consumed within the first hours post mortem. Nevertheless, after catching, the fish begins to stiffen; this event is called rigor mortis. The fresh flesh that is in rigor mortis state, is difficult to fillet and process, and is not suitable for smoking.
Why is it important to avoid animal stress?
Immediately after a fish is dead different changes begin to occur. Deterioration and spoilage are the main processes that take place. This is caused primarily by the chemical breakdown of the flesh by fish enzymes and by enzymes produced by naturally occurring bacteria. Freezing the animals at an early stage can effectively stop spoilage changes. While the fish is alive, energy storage takes place in chemical compounds (ATP). ATP is used for swimming and other cellular needs. It is replenished through a process requiring oxygen. As the fish struggles during capture, they deplete their supply in ATP and oxygen and begin to produce ATP through an alternative pathway that also produces lactic acid. After death, fish can no longer regulate flesh pH (acidity or alkalinity). Enzymes break down ATP to compounds that are associated to off-flavours in "stale" fish, flesh temperature remains high and the flesh remains slightly acidic. The harder the animal struggles during capture and or thrashing around the deck of a fishing vessel, higher temperature and higher pH (acidity). Poor handling after capture can easily result in rapid quality loss and deterioration.
Given the diversity of slaughtering methods used in farmed fish, research has been done to assess how these methods affect fish quality during chilled storage. Common methods in the aquaculture industry are sedation by CO2 and direct gill cutting. Recently, the interests in alternative methods have evolved and commercial use of electro-stunning and various types of brain destruction techniques are currently either in development or at use, as it has been developed in other farmed animals.
Handling operations prior to slaughter should be done with care and minimising stress. Prior to slaughter, fish are not fed. The reason for this to be done is to improve conditions for the fish during the period before slaughtering.
It is important that the persons involved in this action at the fish farm have the knowledge and skill necessary to perform these tasks humanely and efficiently. They must be quick and cause the lowest level of stress. Any struggling at this level, will lead to a decrease in muscle ATP and hence resulting in much less quality fish product. The methods used in aquaculture are much more humane than in fishing, in which the fish are allowed to suffocate in the nets.
Moreover, intense research is currently being done on a new generation of anaesthetics. These are based in "natural products", normally plant-extracts, rather different than the artificially produced chemicals. These artificial chemicals that are diluted in the water to anaesthetize the aquatic animals, may remain in the environment and be difficult to eliminate. The new products give similar efficacy and will result in environmental friendly action and no adverse effects
Extracts from:
Report on the welfare of farmed fish. Surrey, UK: Farm Animal Welfare Council, 1996.
http://www.fawc.org.uk/fish/fishrtoc.htm
Council's Report on the Welfare of Farmed Fish. 1988. Animal Welfare Division. The Ministry of Agriculture, Fisheries and Food. 5th Floor. 1A Page Street. London SW1P 4PQ
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