The present invention relates to a system for delousing fish using warmed water.

A number of lice treatment methods exist where fish are transferred from their pen or cage to an intermediate holding or treatment basin for delousing, after which the fish are passed back to the pen after a predetermined treatment time. The most common delousing method is a chemical treatment in which chemicals are used that are intended to kill the lice. Chemical-free control of sea lice is regarded as being desirable from environmental and fish welfare perspectives. Other lice treatment methods that have been considered are, e.g., shielding, breeding, cleaner fish/mussels, mechanical removal, vaccination, electric current, laser etc.

The disadvantage of traditional fish treatment systems is that it takes time to transfer a certain amount of fish to and from the intermediate holding or treatment basin, at the same time as a minimum treatment time must be ensured. To be sure that all fish are able to remain in the intermediate holding or treatment basin for a sufficient period of time, the removal of fish from the intermediate holding or treatment basin cannot be started until the minimum treatment time has elapsed after the admission of the last fish into the intermediate holding or treatment basin. Since it takes time to move the fish both in and out of the intermediate holding or treatment basin, the time the fish are out of the pen will be considerably longer than desirable. Some fish will thus have a residence time that corresponds to most of the transfer time from pen to intermediate holding or treatment basin, minimum treatment time plus the whole transfer time from intermediate holding or treatment basin back to pen ("first in, last out"). This will cause a substantial degree of stress for a large proportion of the fish that are treated.

It has been shown that warmed water is an effective method for delousing salmon and trout.

Subjecting the lice to a sudden temperature increase gives them a shock. As the lice have very little mass compared to the host fish, the lice will be heated substantially faster than the fish, and the heat shock will result in the lice releasing their grip on the host fish. Once the lice have let go, they can easily be filtered out of the treatment water and destroyed in a suitable way. With the right treatment temperature, the shock to the lice can occur after between about 20 and 30 seconds, the host fish barely experiencing any heating of significance in the course of this short time. After the treatment time of about 20 to 30 seconds, the host fish should be transported as quickly as possible back into the sea to avoid unwanted heat stress, i.e., stress as a result of an undesirable temperature increase of the host fish. NO 332298 (Fig. 1) relates to a lice treatment loop for marine organisms, where the fish are sucked out of the pen in which they live using a vacuum pump and released into a treatment loop after the seawater has been filtered off with the aid of a filter box. In the treatment loop, the fish, and thus the lice, are exposed to lukewarm water. After a certain treatment time, the fish are returned to the pen in that the treatment water and the fish are separated in another filter box, after which the treatment water can be filtered to remove lice, aerated, oxygenated, reheated and used again, i.e., the treatment water is recirculated in the treatment loop. The treatment water forms a closed system that is insulated from the seawater. In this way, the temperature and quality of the treatment water can be carefully controlled, whilst the lice that have detached from the fish can be filtered off and disposed of.

NO 332298 comprises an essentially continuous lice treatment system without any need for an intermediate holding or treatment basin of the type into which the fish are released and allowed to swim freely in until the minimum treatment time is reached and the fish are then sucked out and returned to a pen. In that the fish are gently forced to move through the treatment system, the circulation pump for circulating the treatment liquid in the closed system can be adjusted to ensure that the treatment time is neither too short nor too long. NO 332298 also allows a partial batch treatment to be carried out in that the inlet alternately supplies two or more pipelines with fish, the circulation pump in the pipeline or pipelines into which fish at a given time are not admitted being adjustable so as to ensure the residence time is neither too short nor too long. Today there is also a fairly similar alternative system consisting of two parallel tanks, each with a paddle wheel. A fish pump transports fish from pen to treatment unit and a movable chute delivers the fish alternately to one of the treatment tanks, fish and seawater being separated before the fish are released into the treatment tank. A paddle wheel is used to push and move the fish through the tanks. The paddle wheels turn non-synchronously in order to prevent, to the maximum extent possible, mechanical squashing of fish on their way into the tank by the paddle vanes. Rotation of the paddle wheels forces the fish through the treatment water and out across a water separator before the fish are returned to the pen.

In thermal treatment systems, the treatment temperature is, inter alia, calculated on the basis of seawater temperature (and thus the fish temperature), the number of fish, fish volume/mass, volume of available treatment water etc. As at 2017, the temperature of the treatment water may not under any circumstances exceed 34 degrees; this is governed by special rules. It is assumed that the tolerance level of the fish is higher, but at present this has not been documented, and until new documentation exists, it is not permitted to subject the fish to treatment water having a temperature in excess of 34 degrees.

It has been found that the treatment form using warmed water is very sensitive to temperature fluctuations: a reduction of as little as 0.3 degrees has been found to reduce the treatment effectiveness to a detectable degree. As the fish to be treated have seawater temperature before they are passed into the treatment system, the fish will cool the treatment water to such an extent that the treatment time must be prolonged or else the lice will not get the treatment shock required for them to let go. In the last-mentioned case, the treatment will not give a (desired) result. For example, the treatment water may have a temperature of 34 degrees in the water bath after the last batch of fish has been forced out and the treatment water filtered and reheated, whilst the fish have a temperature of 10 degrees. The volume and thermal capacity of the fish that are passed into the water bath are so large that the temperature in the water bath is reduced to about 32 degrees. This temperature difference is sufficiently large to require, at best, an increase in the treatment time, and, at worst, the treatment will have a strongly reduced effect, which in turn affects the treatment capacity and/or treatment effect of the system.

It is therefore an object of the present invention to provide a system that helps to increase control of the treatment temperature under varying temperature conditions.

It is a further object of the invention to provide a system that reduces the total treatment time to a minimum (time the fish are out of the pen). It is yet another object of the invention to provide a system that reduces the stress to which the fish are subjected and thus enhance the welfare of the fish.

It is a further object of the invention to provide a system that is favourable from an energy economic point of view.

At least one of these objects is obtained with a system that is characterised by the features disclosed in attached independent claim 1. Additional advantageous or alternative embodiments are disclosed in the dependent claims.

A detailed description of some possible embodiments of the invention is given below with reference to the attached drawings, wherein:

Fig. 1 is a schematic illustration of an example of the prior art; Fig. 2 is a schematic illustration of an embodiment of the invention in its most general form; Fig. 3 is a schematic illustration of a possible embodiment of the invention; and Figs. 3-7 are schematic illustrations of other possible embodiments of the invention.

The figures show a lice treatment system for fish comprising an inlet 1, a first separator 2, a liquid bath 3, a second separator 4 and an outlet 5. The liquid bath 3 is formed of a pipeline. By pipeline is meant some form of conduit where there is full control of the inlet and outlet of treatment water and fish, i.e., a closed system in a process engineering sense. This is important because it is desirable to have control of as many parameters in the system as possible, such as water filling volume and time, the time it takes to introduce a given volume of fish, the residence time of the fish in the liquid bath, the time it takes to remove the fish and the treatment water from the pipeline etc. Since the liquid bath 3 is formed of a pipeline, the fish are emptied out together with the treatment water and the fish are separated in the second separator. The fish are then returned to the pen after the treatment and the subsequent separation, whilst the treatment water is filtered, reheated, oxygenated etc. before it is recirculated to the pipeline through a separate inlet 6 prior to a new batch of fish being admitted to the pipeline/water bath 3. Said filtration, reheating and oxygenation, together with a buffer tank and a circulation means, form a primary heating circuit 7, where the sequence of the treatment steps can be chosen. It is basically also optional whether to filter, oxygenate and buffer the circulating treatment water, although it is considered advantageous. In any case, the primary heating circuit comprises a heating element 8. The heating element 8 may comprise a heat exchanger, immersion heater, heating plate, an induction heating element, use of microwaves or the like.

The separators 2 and 4 can, for example, preferably comprise filter boxes, but other solutions that in an efficient and controlled manner separate seawater and fish are possible. What is most important is that the treatment water into which the fish are passed is kept separate from seawater and that the fish are treated as gently as possible. It is also conceivable that more separators are used before and/or after the liquid bath 3.

When the pipeline 3 has been filled with heated (and optionally filtered and oxygenated) water and the fish are admitted into the liquid bath, the temperature of the water will inevitably fall a little due to the lower temperature of the fish. As mentioned, it is not possible to fill the liquid bath with water that has a temperature higher than 34 degrees (as at 2017). The fall in temperature of the treatment water will vary according to the temperature of the seawater/fish and the size of the fish. The fall in temperature will thus also be partly dependent on the time of year. Since the treatment time is dependent on the treatment temperature, and the treatment temperature varies with the fall in temperature, this results in elements of uncertainty that are both unpredictable and undesirable. To remedy this, the invention proposes the use of a secondary heating circuit 9 that is designed to discharge a part of the treatment liquid from the liquid bath, in order then to replace it with treatment liquid that has been heated to a higher temperature than the treatment liquid that was discharged. The treatment water is discharged through a separate outlet 10, e.g., a drain, from the pipeline, which ensures that the fish remain in the liquid bath and are not released until the treatment is finished. This must take place in a controlled manner and as quickly as possible as the aim is to shorten and control the treatment time and the time the fish are out of the pen.

As an example, it is conceivable that 1/3 of the water is emptied out through said drain in the course of 5(?) seconds, whilst a corresponding amount of water at 34 degrees is pumped into the pipeline. If the water discharged had undergone a fall in temperature of 1 degree when the fish were admitted, the temperature in the liquid bath would be increased by about 0.3 degrees with the aid of the secondary heating circuit. If it is permitted to introduce water having a higher temperature than 34 degrees (provided that the overall temperature in the heated bath does not exceed 34 degrees), it would be possible to adjust the temperature in the liquid bath up closer to the current limit of 34 degrees.

The treatment time and treatment temperature are dependent on several factors, such as sea temperature, the time the fish/lice have been exposed to the sea temperature in question, the temperature difference between sea temperature and the temperature of the treatment liquid after having been through the primary heating circuit etc. Empirical tables have been drawn up that indicate the ratio between these and other parameters, and which lastly provide guidance as to how much reheating is necessary and what the correct treatment time will be.

The water that is discharged from the liquid bath 3 into the secondary heating circuit 9 must be heated by a heating element. In an embodiment, the heating element in the secondary heating circuit 9 may be the same as the heating element 8 in the primary heating circuit 7, i.e., that both circuits share the same heating element 8. Alternatively, the secondary heating circuit 9 may be isolated from the primary heating circuit 7, such that it uses a separate heating element 8'.

If the secondary heating circuit 9 shares heating element 8 with the primary heating circuit 7, it is also conceivable that the treatment liquid that is to be reheated is passed through the other treatment steps, i.e., filter, oxygenation, buffer tank etc., and that the same circulation means 10 is used for both circuits.

The circulation means 10 may be a suction pump, impeller, vacuum pump, propeller or the like. Alternatively, the secondary heating circuit 9 can, as mentioned, have a separate heating element 8' as well as a separate filter and oxygenation system, its own buffer tank and a separate circulation means 10'.

The reason it is advisable to have what here is called a secondary heating circuit 9, is that it is not desirable to circulate the water out via the second separator 4. To ensure that the fish remain in the liquid bath 3 whilst the heating takes place, the liquid bath must comprise a separate drain 10 that does not allow fish through, only water.

In an alternative embodiment of the invention, the capacity can be scaled up by providing two or more pipelines in parallel. The parallel pipelines can thus be filled, heated, left to stand and lastly be emptied in such a synchronous manner that the primary and secondary heating circuit serve both or all the parallel pipelines. Thus, for example, the third pipeline can be filled with fish whilst the second pipeline is filled with treatment water from the primary heating circuit and the first pipeline is emptied of treatment water and fish across the second separator. The treatment water from the first pipeline that is separated out of the second separator is admitted into the primary heating circuit whilst the fish are returned to the pen. At the same time, the treatment liquid is reheated in the fourth pipeline and in the fifth pipeline the fish remain more or less stationary whilst the heat treatment is under way and the sea lice release their grip. When the third pipeline has been filled with a predetermined and/or sufficient volume of fish, the warming up of the water (the third pipeline) starts, whilst filling of fish starts in the second pipeline and emptying of treatment liquid and fish across the second separator is commenced in the first pipeline etc., etc.

The advantages of the invention become more evident if a plurality of pipelines are used. The invention permits the temperature fall in a pipeline to be compensated for whilst the treatment liquid in the pipeline, in processing terms, "stands still" with the aid of the secondary heating circuit whilst the primary heating circuit supplies a second pipeline with "new" treatment liquid. In this way, the different systems are used to the maximum and the process of sucking fish into the treatment system runs more or less continuously. Such a system can be scaled such that it has a capacity of, e.g., 300 tonnes/hour. By adding more pipelines and/or upsizing the pipelines, the system can be given an even larger capacity.

In an embodiment comprising several pipelines/liquid baths 3, the inlet 1 can comprise, e.g., a branched pipe or a valve box (not shown). The fish and the seawater can be sucked in through each of the inlets with the aid of underpressure that is produced by a vacuum pump that is connected to or shared between each of the pipelines.