NO347174B1

NO347174B1 - System and method to sort fish

Info

Publication number: NO347174B1
Application number: NO20210366A
Authority: NO
Inventors: Gunnar Hoff
Original assignee: Cflow Fish Handling As
Priority date: 2021-03-23
Filing date: 2021-03-23
Publication date: 2023-06-19
Also published as: NO20210366A1

Description

System and method to sort living fish

The present invention relates to a system and a method for sorting living fish, according to the preamble of independent claims.

Background of the invention

Aquaculture is one of Norway’s most important export industries. By 2016, seafood exceeded 12 per cent of total Norwegian exports, by value. Norway accounts for more than 50 % of global salmon farming, and the annual revenue is more than 65 billion kroner. Most of the fish are grown at fish plants containing cages in the ocean, even though onshore plants are in progress. Farming of other swimming species, such as shrimps, are also increasing.

Fish and other species are transferred to cages when they have the correct size and/or age, and are fed until they should be transferred to another cage, for further growth, slaughter or other handling. To remove fish from a cage, the volume of the cage being available to the fish is usually reduced, either by draining off water, in case of closed walls of the cage, or elevating the bottom, in case the cage is a regular fish cage. Then fish and water is pumped out of the cage, and transferred to a new location.

When the volume available to the fish in the cage is reduced, the fish will be forced closer together, and the amount of water per fish is reduced. This stress the fish, and is disadvantageous as stressed fish has increased death rate if the fish should continue growing, and as the quality of the meat after slaughter may be greatly affected.

It is said that the weight of feed per gram of fish is closing up to 1, but not all fish eat the same amount of feed, and not all fish grow at the same rate. Even if the fish is exactly the same age, the size may thus be different, and there is a need for sorting/grading the living fish depending on size, in order to remove only fish larger than a set size, and to keep smaller fish for further growth. Traditional handling of fish during transportation involves pressure differences and pumps, and the fish may get injured, or get reduced viability.

One way of grading living fish is described in US 3,951,104, using two enclosures separated by a wall having grading openings. This system however, needs a type of attractant such as food in one tank, to attract the fish. All fish, regardless of size will be attracted by the attractant and the larger fish may block the openings, and prevent the smaller fish from getting into the other enclosures.

NO890628 describes another way of grading living fish, using a net arranged between enclosures, and then reducing the enclosure containing fish. The net has a grader and the reduction of the enclosure will force the fish being small enough to go through the grader. However, larger fish may block the openings of the grader and reduction of the size of the enclosure will stress the fish. Yet another way of grading living fish is described in WO 94/17657 where natural current is used to attract the fish from one enclosure to another. However, as natural current vary, the swimming direction of the fish will vary accordingly.

Based on the above, there is an object of the present invention to develop a system and a method for grading living fish in a tank without or with minimal handling and stressing of the fish. Another object is to remove only fish above a set size from a tank, and to avoid handling and stressing of the fish to be kept in the tank. Yet another object is that it should be possible to use the system and method both on new and existing fish tanks, and preferably on traditional fish cages at sea.

Summary of the invention

The objects are met by a system and a method according to the characterizing parts of the independent claims. Further advantageous features are given in the corresponding independent claims.

The invention relates to a system for grading or sorting swimming fish in water, according to their size. The system comprises a first tank containing the fish to be graded, and a second tank connected to the first tank by a passage, wherein a grader is arranged in the passage. At least parts of the tanks and the passage are filled with water, to allow the fish to be submerged and able to swim at all times. The system further comprises means arranged to estimate the water flow in the passage, a device for generating flow in the passage and a control unit to operate the device for generating flow in the passage based on the estimated water flow. The system further comprises closing means for closing the grader, wherein the control unit may operate the closing means based on the estimated water flow.

By swimming fish, it is herein meant a living fish being able to swim. "Grading" and "sorting" are both used to describe that the fish are separated according to their physical size, wherein smaller fish are able to swim through the grader and into the second tank, while larger fish are retained in the first tank.

The tanks may be any suitable tank, container or cage for farming fish, which would be obvious to a skilled person. A preferred tank is a fish cage, floating in water at the sea. The first and second tank may be separate parts of the same physical tank, two separate tanks arranged side by side at all times, or two tanks may be arranged in relation to each other when the fish in the first tank should be graded. The tanks may be identical or different, for instance, as the second tank may be a temporarily tank used only during the grading, and as the second tank never will contain all the fish in the first tank, the second tank may be smaller.

The passage arranged between the first and second tank may be arranged in any suitable manner. For instance, if the tanks are arranged at a distance from each other, the passage may be shaped as tunnel, however, if the tanks are next to each other, or separate parts of the same container, the passage may simply be an opening in both tanks whereby the openings are lined up and connected to each other. The passage may be arranged in any direction, horizontal, vertical or sloping without deviating from the scope of the enclosed claims.

In a preferred embodiment, the passage and the connections between the passage and the tanks are provided with mutual cooperating means, such that the passage may be assembled and disassembled easily and quickly, with minimum manual work required.

In an embodiment where the tanks are separate parts of the same physical container, the passage may be integrated in a separation wall between the tanks. The wall may be of solid material or of a net, and may even be a bulkhead in a fish carrier vessel. The sizes of the tanks may be fixed or adjusted by moving the separation wall.

In another alternative embodiment, the second tank is submerged into the first tank, and the passage between the tanks is the opening into the second tank. The wall of the second tank may be of solid material or of a net.

A grader is arranged in the passage, the grader has openings allowing fish smaller than a set size to swim through, and preventing larger fish from swimming through. The grader may comprise vertical and/or horizontal bars, or a grid. In an alternative embodiment, the size of the openings through the grader are adjustable, in order to select the size of the fish allowed to swim through. In another embodiment, the grader may easily be replaced by a grader having openings of another size.

The grader may be arranged in the middle or at any one of the ends of the passage. However, in a preferred embodiment the grader is arranged at the end of the passage being at the first tank. Thereby any fish being too large to pass through the grader, will not get into the passage and will not block the system. When the tanks are arranged next to each other, or being separate parts of the same container, the grader may be fastened directly to both tanks and constitute the passage.

A system according to the present invention further comprises means arranged to estimate the water flow in the passage, in the following also referred to as "estimation means". The flow "in the passage" will be the same as the flow "through the passage", and is the flow of water from one tank to the other tank. The means may be arranged in the passage, at the outlet or inlet to the passage or any other suitable place to estimate the rate and direction of the water flow through the passage, which will be obvious to a skilled person. When the tanks are open fish cages arranged in the sea, both tide, wind and waves will influence the rate and the direction of the water flow. The means may for instance be a sensor which measures the flow.

The term "estimate" and "estimated" in relation to the water flow should be interpreted broadly to include both calculated values and values estimated on observations as well as values being measurements from a sensor.

In order to make the fish voluntarily swim through the passage and grader and into the second tank, the water flow through the passage must be from the second tank and into the first tank, as fish swim counter flow. The grader, being arranged in the passage, will only allow fish below a set size to swim through. The system further comprises a device for generating flow in the passage as well as a control unit to operate the device based on the estimated values for water flow as mentioned above. The control unit and the estimation means will ensure that the device is operated to keep the flow through the passage within the given range, in the given direction.

As an example, if the estimated flow of water through the passage is too low, the device will be operated and generate additional flow. Further, if the estimated flow of water through the passage is too high, the device may be operated to generate a flow in the opposite direction, and thus the resulting flow through the passage will be reduced. In a similar matter, if the estimated water flow is in opposite direction, that is from the first tank to the second tank, the device will be operated to keep the flow through the passage within the given range, in the given direction.

The device for generating flow may be a propeller, a thruster or the similar. In a preferred embodiment, the flow of water should be above 0,02 m/sec through the passage, from the second tank to the first tank. In a more preferred embodiment the flow should be in the range 0,019 - 0,08 m/s. If the flow of water becomes too high, such as 1 m/s, the fish will not swim, but rather be standing in the flow. If the flow of water is too low, the fish will not be tempted to swim through the grader.

When the flow is within the preset range, fish in the first tank will swim in countercurrent direction, and thus they will try to swim through the passage and through the grader. Fish being smaller than the openings in the grader will enter the second tank, while fish being larger will remain in the first tank. In this way, the fish is graded, and smaller fish is kept in the second tank, while larger fish are retained in the first tank. The larger fish may then be removed, for instance, transported to slaughter, and the smaller fish may be kept in the second tank, or transferred back to the first cage for further growth.

The system comprises means for closing the grader, wherein the control unit may operate the means based on the estimated water flow. By "closing the grader" it is herein meant that the openings through the grader is reduced until no fish may swim through, but preferably allowing water to flow unhindered. The means for closing the grader, in the following also referred to as "closing means" may be in addition to or instead of the device for generating flow. In such an embodiment, when the estimated flow is outside of an outer set range, the grader in the passage between the tanks will be closed until the estimated water flow is within the outer set range. The outer set range relating to closure of the grader may be different from the set range relating to operating the device for generating flow in the passage. The closing means may be advantageous if the flow generated by the device is not sufficient to bring the resulting flow into the set range, for instance during rough weather, or if the device has been running continuously for a long period of time. It may also be advantageous to close the grader after the sorting is performed, to prevent the smaller fish from swimming back into the first tank, regardless of the flow through the passage.

The estimation means and the device for generating flow and/or closing means, are arranged to communicate through a control unit. The desired value or range for flow through the passage is set in the control unit, any estimated waterflow made by the estimation means are compared to the set value, and based on any deviation between estimates and set range, the device will be operated. The control unit may also be arranged to communicate and report to an operator, and may include a storage for storing measured flow and operations of the device for generating flow.

In embodiments comprising means for closing the grader, the outer set range for flow is also set in the control unit, and if the estimates for water flow are out of the outer set value, the closing means will be activated as described above.

In an alternative embodiment of the invention, a one way valve is arranged in the passage, preferably closer to the second tank than the first tank. The valve will allow fish to pass through in one direction only and prevent any fish in the second tank to swim back into the first tank, regardless of the water flow through the passage.

In a preferred embodiment, the first tank further comprises means for reducing the volume available to the fish. The means are arranged such that the passage to the second tank will be in the volume available to the fish. Such means are well known to a skilled person, for instance by elevation of the bottom of the tank, a separate net inserted on one side of the tank, such as a purse seiner, or the similar.

The invention further relates to a method for grading swimming fish in a first tank, by using the system described above. The method comprises the following steps a) estimating the water flow in the passage by the means for estimating, b) comparing the estimates to a set range for water flow in the control unit, c) operating the device for generating flow in the passage.

In a preferred embodiment steps a-c are repeated continuously. In another alternative embodiment, the a-c steps are repeated at regular intervals.

If the estimate for water flow is out of outer range, and/or the device has been running for a predetermined amount of time, for instance 12 hours, the device should be stopped, and the grader closed.

In a preferred embodiment, the method also comprises a step for reducing the volume available to the fish in the first tank. By reducing the volume, more fish will swim through the passage.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

Description of the figures

The invention will now be described by the enclosed figure, showing a system according to the present invention. The different parts of the figure are not necessarily in scale to each other, as the figure is merely for illustrating the invention.

Figure 1 shows a first fish tank, shown as a fish cage having a net wall 1a connected to a conical net bottom 2a. The net wall 1a is hanging from a floating collar 3a arranged at the surface of the sea. The figure also shows a second fish tank, shown as a corresponding fish cage, having a net wall 1b connected to a conical net bottom 2b. The net wall 1b is hanging from a floating collar 3b arranged at the surface of the sea.

In the shown embodiment, both cages are shown in cross section, and only half of the cages are shown. The second cage is shown on the left, and only the right half of the cage is shown. Correspondingly the first cage is shown on the right, and only the left half is shown. Further, the shown second cage is smaller than the first cage on the right.

In the net walls 1a, 1b of the cages there are openings 4a, 4b arranged adjacent to each other, and a passage 5 is arranged between the openings, and connects the cages. At the opening 4a of the first cage, a grader 6 is arranged. In the shown embodiment, the grader is a number of horizontal bars arranged at a distance, and thus the grader looks like a dotted line in Figure 1. The distance between the bars will be determining for the size of the fish being able to pass from the first cage to the second cage.

In the second cage, a device 7 for generating flow in the passage is arranged at distance from the passage. In the shown embodiment, the device is a thruster 7, having a propeller arranged to generate flow through the passage. The system further comprises means arranged for estimating the water flow in the passage 5, in the shown embodiment the means are a sensor 8 arranged in the passage, between the first and second cage.

The sensor 8 and the thruster 7 are both connected to a control centre (not shown), which will operate the thruster 8 based on the measurements from the sensor 7. If the sensor estimates values being lower than a preset value, the thruster will be started to generate a flow which will increase the flow through the passage.

Correspondingly, if the waterflow is too high, the speed of the thruster will be reduced, and further, if necessary, the thruster will be operated to create a water flow in the opposite direction.

Once the flow is within the preset range, normally about 0,019-0,08 m/s, fish in the first cage will swim in counter-current direction, and thus through the grader, that is between the shown horizontal bars. Fish being smaller than the distance between the bars will enter the second cage, while fish being larger than the distance, will remain in the first cage. In this way, the fish is sorted, and smaller fish is kept in the second cage, while larger fish are retained in the first cage.

The example above is given to illustrate the invention and should not be used to interpret the following claims limiting. The scope of the invention is not limited by the example give above, but the following claims. Modifications and amendments of the invention, being obvious to a person skilled of the art, should also be included in the scope of the invention.

Claims

1. System for grading swimming fish in a tank, the system comprises a first tank containing the fish to be graded and second tank connected to the first tank by a passage and a grader arranged in the passage, characterized in that the system further comprises means arranged to estimate the water flow in the passage, a device for generating flow in the passage, a control unit to operate the device for generating flow in the passage based on the estimated water flow, and closing means for closing the grader, wherein the control unit may operate the closing means based on the estimated water flow.

2. System according to claim 1, characterized in that the means arranged to estimate the water flow in the passage, is a sensor arranged to measure the flow.

3. System according to claim 1, characterized in that the device for generating flow will be operated to keep the flow in the passage above 0,019 m/s from the second tank and into the first tank containing the fish to be graded.

4. System according to claim 3, characterized in that the device for generating flow will be operated to keep the flow in the passage in the range 0,019- 0,08 m/s.

5. System according to any one of claims 1-4, characterized in that at least the first tank is provided with means for reducing space available to the fish.

6. Method for separating fish in a first tank, by using a system according to claims 1-5, characterized in that the method comprises the following steps:

a) estimating the water flow in the passage by the means,

b) comparing the estimates to a set range for water flow in the control unit, c) operating the device for generating flow in the passage in response to the result of step b).