The invention relates to a method, as indicated in the introductory part of claim 1, for applying electronarcosis to fish, as well as an arrangement for performing this method.

Background

It is known to paralyze fish that are to be slaughtered, by immersing them into cooled water with added CO ₂ . In some countries which have restrictions on the use of CO ₂ for this purpose, it has been necessary to seek alternative methods for paralyzing.

It is known to apply electronarcosis to fish to reduce stress and thereby to yield better quality of the fish that are to be slaughtered. From patent publication EP 1 143802 (Møller and Roth), it is known to guide the fish in an electric field with a field strength of about 1.25 volt/cm, with a frequency of above 20 Hz. This requires equipment, which must be biased in the region of 280 volts in water. This is inappropriate in an industrially adapted slaughtering process.

At the Silsoe Research Institute in Great Britain, experiments with paralyzation offish have been performed, by placing the fish in a water tank and conducting an alternating current of 350 mA through the fish at a frequency from 50 to 2000 Hz. The use of water as a transferring medium makes the equipment complex and makes the process lengthy.

From patent publication US 5.327.854 (Smith et al., 1994) it is known to paralyze fish in a water- conducting tube that extends through the water between two electrodes. However, this also is not suitable for industrial use with fish slaughtering.

From German publication 2321 646 (Hauni-Werke 1974), it is known to paralyze fish by placing it in an electricity-conducting fluid in a gutter, with an electrode at each end, and applying voltage pulses to the electrodes. A frequency of 40 - 50 Hz and 400 volts as a necessary voltage, are mentioned as an example.

From PCT-application with publication number WO98/44805 (Indac Ltd 1998) it is known to kill a fish by applying two electrodes against the head of the fish. However, this method is not suitable for mass paralyzation of fish, due to inefficient handling of the fish and the problem of reducing the effect to paralyzation only.

Hence, there is a need for an arrangement that is suitable for paralyzing fish, that are to be slaughtered in a fish slaughterhouse, that is easier to handle during slaughtering.

Object

The main object of the invention is to provide a method and an arrangement for applying electronarcosis to fish in an easier and more secure way than what has been possible with the prior art, so that the slaughtering process can be performed efficiently and provide good quality slaughtered fish. It is desirable that this takes place without the use of water and with equipment that does not create any risk of hurting the fish, for instance by burn injuries.

It is important that the fish is not exposed to stress during the slaughtering process, so that rigor mortis does not occur quickly. By avoiding exposure of the fish to stress, the lasting ability is prolonged.

Another object of the invention is to make the equipment that is required for performing the method for applying electronarcosis as simple and efficiently usable as possible.

The invention

The invention is stated in claims 1 and 4, which describe a method and an arrangement for performing this method, respectively.

Primarily, the invention provides a possibility for combining simple equipment with efficient and quick treatment. It is also established that the resultant paralyzation is appropriate for the quality of the slaughtered fish and for the slaughtering process. It is established that fish, which is slaughtered after electronarcosis as applied according to the invention, stays fresh approximately as long as fish slaughtered one by one under optimal conditions regarding the stressing of the fish.

In claims 2 - 3 and 5 - 10, special features of the invention are stated.

Further details of the invention will appear from the following example description.

Example The invention is further described below, with reference to the drawing, in which

Fig. 1 illustrates a schematic perspective view of a fish gutter that is made using an arrangement according to the invention,

Fig. 2 illustrates a cross-section view of the fish gutter in Fig. 1, with a fish passing there through, Fig. 3 illustrates a cross-section side view of an alternative embodiment of the invention, and

Fig. 4 illustrates a front view of an additional embodiment.

Fig. 1 shows a gutter 11 with parallel side walls 12, 13 and a V-shaped bottom 14, which is arranged with an inclination from an inlet end towards an outlet end. The gutter 11 is made of an electrical isolating material, such as plastic composite.

Three bar-shaped carriers 15, 16, 17 are mounted across the gutter 11, at uniform spacings apart. The carriers 15 - 17 each carry a row of downwardly extending threads 18 of metal or other conducting material, which are freely bendable and which extend down to a level at the lower edge of the side walls 12, 13. The threads in each row are connected to a voltage source 19 that applies a voltage with alternating magnitude from row to row 15 - 17. In an example, the voltage was twelve volts direct voltage between two neighbouring rows.

Fig. 2 shows an example of how a fish passes a row of bendable threads 18, in such a way that at least one thread, two treads in the example, from each of the carriers 15 - 17, are simultaneously in contact with the fish. Thus, the fish will be exposed to a voltage impulse, which triggers a corresponding short-lasting, low current through a part of the fish. The required duration of this current will depend on various conditions, such as the size of the fish and the shaping of the electrodes. It has been found that the current impulse can be short-lasting, with a lower limit at about 0.1 second.

With this equipment and method, the fish was put into electronarcosis or paralyzed for a period of 0.5 to 2 minutes. In this period it was calm, without force in the movements. This made the slaughtering process more efficient.

The electronarcosis could take place without the fish being marked. This means that the method does not unnecessary harm the fish.

Tests have been done with fish that is slaughtered during electronarcosis. They show that the fish does not develop rigor mortis faster than for common fish slaughtering. That means that it is not exposed to stress that triggers enzyme formation and early stiffening.

Figure 3 shows an alternative design of an arrangement for the treatment offish according to the invention. Here, a tube-shaped channel 20 with a J-shaped path is arranged. Pn the bend of the channel 20, a plate-shaped metal electrode 21 is arranged on the outer wall, which electrode 21 expands about 45° out to each side and which is connected to a voltage source (not shown), through a cable 22. Diametrically towards the metal electrode 21 are directed four rows of bendable metal threads 23 with three in each row. These metal threads 23 are connected to a joint cable 24 that is also connected to the voltage source (not shown), with a potential difference to the metal electrode 21 of twelve volts.

Fish that were led through the channel 20 with voltage applied through the metal electrode 21 and the metal threads 23, were paralyzed in the corresponding way as in the example above.

Modifications The electrodes for applying electrical voltage to the fish can be shaped in various ways, with at least a bendable, thread-shaped or revolvable strip- or plate-shaped electrode. The number of electrodes and their layout can vary with respect to the above examples.

The gutter, through which the fish is led, is used as a carrier for the one or the plurality of bendable thread-shaped electrodes. The gutter can also totally or partially be made of a conducting material, particularly stainless steel, so that this part can constitute an electrode.

Fig. 4 shows a gutter 25 of stainless steel that forms an electrode, and three plate ribbons 26 of a conducting material, especially metal, which at the end are revolvably suspended with a sleeve 27 on a carrier rod 28 and which form the other electrode.

The applied voltage can be in the range of 5 to 30 volts, depending on the type of fish and its size. Experiments with application of direct voltage have been made. However, it is also possible to use alternating voltage, for instance with a frequency of between 50 and 200 Hz.

The arrangement according to the invention is preferably run in a dry state, i.e. without adding water. But there might be fields of use where water is used as a transportation medium.

The invention provides for the possibility for various electrode structures, with one, two, or more electrode sets after one another along a travel path of the fish, as one of the electrodes can be plate shaped and placed in or be made of the structure that leads the fish.