This manually operated slaughter machine for trout removes the guts with a vacuum which ensures hygienic conditions.
“Fish slaughter” can be understood in different ways: It generally comprises preparatory measures for the slaughter process, then the stunning and actual killing of the fishes, as well as gutting. In the past the focus was primarily on efficiency and profitability. Today, efforts are also made to avoid unnecessary stress for the fishes. This applies both to manual and machine slaughter processes.
The German entrepreneur Hans Raab recently closed his fish farm in the Swiss state of St. Gallen in which he had invested nearly 40 million Swiss francs. On the farm he had produced ‘Melander’, a cross between various catfish species. With this closure Raab put an end to months of dispute with animal rights activists and several media who accused him of ethically unacceptable slaughter methods. The St. Gallen veterinary had declared that “live chilling” – the method used on the farm – was not in accordance with the animal protection directive that had been valid since September 2008. For this technique the fishes (that are farmed in water with a temperature of 27°C) are stunned and de-slimed in a slowly rotating drum filled with flake ice before they are fed into a slaughter machine. Without wanting to judge either the technique or its advocates and opponents, the dispute that arose on its account shows what a significant issue animal slaughter can be, particularly since the discussion of the fundamental process among the public is often very emotional.
Fish slaughter comprises several work stages. Usually at the beginning of the process the abdominal cavity of the dead fish is opened using a cut from the throat to the anus and a central blood vessel is severed to enable bleeding (deviations from this procedure are possible depending on the species: in the case of cod, for example, the throat is cut immediately after the catch). After that, the guts, gills and often the belly skin are removed together with the kidney using a scraper, a brush or suction. The slaughter process is often combined with the heading of the fish which can be performed using a round, wedge, or oblique cut. In the case of the first mentioned technique the collar bone remains on the body, with the wedge cut it is removed, and with the oblique cut, which involves the highest meat losses, the abdominal cavity is opened at the same time.
Traditional slaughter methods under scrutiny
European law demands that animal slaughter should be carried out without avoidable pain and suffering to the animals. Although the pertinent rules and regulations deal primarily with agricultural livestock they also apply to fishes. A stress and pain free slaughter process is also in the interests of the fish farmer since there is in the meantime adequate proof that humane killing leads to measurable increases in meat quality and often to a longer shelf-life. Some traditional slaughter methods were preferred because they were inexpensive, simple and reliable. Today, however, techniques like live gutting, suffocating in the air, hypothermia on ice, or CO2 narcosis are considered inhumane in a lot of countries.
Efforts made to spare animals unnecessary stress and pain already begin during the processes prior to the actual killing. To ensure high quality and hygienic final products, feeding is stopped several days before the slaughter date. An empty bowel at the time of slaughter reduces the risk that its contents will contaminate the fish meat. In the opinion of numerous experts the period of fasting should not exceed 72 hours, however. This length of time is sufficient to completely empty the bowel without causing excessive harm to the fish’s well-being. As in this case, compromises are inevitable in other processes, too, for example during harvesting which leads to a concentration of the fishes in a very confined space and often even their removal from the water. Crowding of the fishes and net contact increase the risk of mechanical injuries and reduce the quality and oxygen content of the water. If possible, the animals should not be subjected to such situations for more than 2 hours. With the help of modern methods such as pumping it is possible to avoid stress since the fishes remain in their natural habitat and often even swim to the slaughter facility themselves.
A lot of slaughter facilities thus have water tanks or net cages in the close vicinity in which the fishes can be put for a time after delivery to enable them to calm down and reduce any stress caused by the transport. If fishes are exhausted from the journey to the plant and are then killed directly on arrival, the meat quality is lower. Apart from that, rigor mortis sets in at an earlier point in time with the result that there is less time left for the subsequent processing stages. If fishes are subject to less stress during the slaughter process rigor mortis begins later and is then not so strong either. In Norway’s salmon farming industry experiments are currently being carried out to cut out the transport of live fish altogether. The fishes are killed immediately on specially equipped ships after being pumped out of the net cages and then transported in tanks containing refrigerated salt water (RSW) to the slaughter plant.
Stunning saves the fish unnecessary pain
Although the actual killing process is today mostly carried out using modern methods that are very efficient and hardly cause the fishes any pain or stress it is still the most controversial action in the whole slaughter process and it is viewed very critically by a lot of consumers. That is why it is very important that only methods are used that have been tested and officially approved by the authorities. Technical slaughter facilities have to be serviced and checked regularly to be able to guarantee their functionality. This is naturally of extreme importance in industrial slaughter facilities where thousands of fishes are killed every day. In order to save the fish unnecessary pain they have to be properly stunned or rendered “insensitive” before killing. Under practical conditions these two process steps, i.e. stunning and killing, are often closely linked. At present there are two main techniques that are used for fish slaughter:
1. Mechanical methods
Mechanical techniques for stunning and killing fishes are very effective, safe, and supply irreversible results if they are used correctly. The intended effect is achieved by physical destruction of the brain structure by a slit, a shot (tuna) or a hefty blow to the head of the fish. These methods can be carried out either by hand or by machine. Machine solutions are advisable particularly for large slaughter volumes because during manual work precision and effectiveness will decrease with time. If the fish is only stunned by hitting the next process stage (usually a gill slit to enable bleed-out of the fish) has to take place immediately afterw
ards before the fish wakes up again.
2. Electric methods
The results and efficiency of these techniques depend on the amperage, pulse repetition frequency and the duration of the electric impact. They can thus be used both for stunning fish and for killing fish. If used correctly stunning with electric current is very gentle, and organic damages or increased mortality of the fishes is not to be feared. After electronarcosis the fishes wake up again unharmed after a short time. That is why killing must take place immediately after electrical stunning. One of the advantages of these methods is that they are suitable for use on fishes that are relatively difficult to kill, for example eels or flatfishes.
The following methods for stunning or killing fish are frequently used for some specific species groups:
Blow to the head: cyprinids, wels catfish, salmonids, halibut
Brain stab or drill: salmonids, tuna
Free shot: tuna, swordfish
Electrical techniques: cyprinids, wels catfish, eel, salmonids, tilapia
Manual and machine slaughter methods
Fishes are probably the class of vertebrates that includes the most forms, with species that vary enormously in shape and size. Flatfishes look completely different from salmon or eels, and sprats or sardines are smaller than cod or tuna. Apart from these differences, a lot of species differ greatly with regard to the firmness and structure of their muscle tissue. This makes it almost impossible to design universal slaughter and processing techniques that would work well for a lot of different fish species. Machine solutions have mostly been developed for a particular fish species and are then only suitable for other species if these have a similar shape and size and a comparable bone structure.
The simplest way to get around the problem of different body shapes and other deviations from the norm (length, texture and hardness of the muscle flesh) is to kill and process the fishes by hand. In spite of all sensors, image recognition systems and electronic controls that constantly re-adjust all the tools there is probably no machine that is as flexible as an experienced person who can immediately find the right position for a blow to the head to stun the fish or the belly cut. On the other hand, machines have the advantage that they don’t tire, that they supply constant product performance and that they mostly cause less bacterial contamination than is the case during manual work… particularly since the slaughter process is one of the “unclean” areas of fish processing, in which the staff are constantly subject to wetness, blood and other dirt (slime, scales). This leads to a relatively high sickness rate: the risk of injury is high.
Fish species like salmon that are produced in large quantities in aquaculture and can guarantee consistent full capacity usage of slaughter facilities seem to make even fully automatic slaughter lines a profitable option. In Norway a robot line recently went into operation. It was developed by the equipment suppliers SeaSide, SINTEF Trondheim and Slakteriet Florø, one of the biggest salmon slaughtering plants in the country.
In the salmon slaughter line, image recognition systems and robotics ensure that the gill cut for bleeding – based on the size of every individual fish – is always optimally positioned. The salmon swim proactively into the slaughter line where they are first individually stunned by electricity. This prevents the anaesthetized fishes from getting pushed against or on top of one another which would make the correct throat cut difficult in spite of the image recognition system. Through the combination of exact positioning and electronarcosis the salmon can be killed in an ethically acceptable way, free from any stress and this leads to a particularly high product quality.
Slaughter machines for small and medium-sized companies
However, it doesn’t always have to be a fully automatic slaughter line. There is a broad range of useful machines for artisanal use in smaller companies, too, which kill and process the fish. Such offers mainly address fish farming facilities that process and market some of the fish they produce themselves. Humane stunning and killing plants that work with electric current are in the meantime very widespread, for example. Systems from professional suppliers such as the German company FIAP or the British Ace Aquatect with their High Speed Humane Electric Stunner with which they claim 85% of the trout in the UK are stunned or killed, today come up to all the legal requirements with regard to health and safety in the workplace, hygiene and animal welfare.
In trout farming enterprises slaughter machines like the Salmofix can be very practical. This machine enables the gutting of 300 to 500 fishes in sizes of between 200 and 1,500 g in one work process in an hour so that when they come out of the machine they are ready for smoking. The slaughter head of the Salmofix opens the abdominal cavity with a clean cut and at the same time cuts through the throat. With the help of a vacuum the guts are then sucked out and stored in a hygienic container. A rotating brush at the same time removes the remains of the kidney. The slaughter machines are usually made completely of stainless steel and there is a sink with separate water supply so that the fishes can be thoroughly cleaned immediately after gutting. All these tasks can be carried out one after the other in a single process without the fish having to be put down in between times.
With 1,000 trout per hour the capacity of the fully automatic slaughter machine from AGK Kronawitter is designed for larger companies. This machine can also be used for other fish species whose body shape is similar to that of trout. The fish is placed onto a pick up facility in a forward direction and goes head first into the machine. It is held down so that the abdominal cavity can be cleanly cut open by fixed blades. At the same time both belly flaps are folded to the side so that a gripper can remove the guts completely. Finally a flexible scraper removes the kidney from the carcass and a brush removes any remains. This slaughter machine thus produces kitchen-ready fishes.
The slaughter machine of the Danish company Boleto Maschinenfabrik which works in a similar way is suited to trout, mackerel and other, similarly shaped fishes. Each individual slaughter machine is individually tailored to the needs of the customer so that depending on the fish species and size optimal slaughter results can always be achieved. A particularly challenging fish for slaughter machine developers is the eel, whose elongated, flexible body places high demands on the machine. The eel slaughter machine ST504 from Steen was specially developed for farmed eel in sizes from 110 to 200 g. This machine has a throughput rate of 24 eels per minute. The machine manufacturer Baader offers a very extensive programme of heading and gutting machines for various groups of fishes. The Baader 39, for example, is for heading and gutting Alaska Pollack and other white fishes in a size range from 25 to 40 cm. It does not only produce headed and gutted fishes (up to 200 fishes/ min) but also enables intact recovery of the roe.