NO347262B1 - Fish transport apparatus and a method of exchanging the water or to sort fish in a fish transport apparatus. - Google Patents

Description

Method and apparatus for water exchange or positioning of marine organisms in fish conveying cross-sections using inclined waterflows.

The disclosure relates to the field of fish-farming.

In connection with fish-farming, it is sometimes necessary to transport fish both to move the fish from one location to another or to locate the fish in a system for treating the fish in one way or another or for monitoring or sorting the fish. In this situation the fish move inside ducts with flowing water, and it may be required to change/substitute the water inside the duct or to sort the fish between different ducts or channels. Reasons for changing the water may include to remove water with substances for treating the fish, to remove parasites entrained in the water flow, to introduce water with higher oxygen levels, with different temperature, with different salinity, to remove contaminations, etc. Fish are typically sorted by size, but one embodiment of the invention will also make it possible to sort fish based on other criteria for instance based on image processing of images from a camera monitoring the fish.

Transport of fish as described above is often done in connection with delousing of fish and is generally performed in circular pipes with pipe dimensions around 250 to 300 mm in diameter. The relatively small pipe diameters are largely used in order to prevent multiple fish from being transported through the pipe simultaneously, thus preventing overlap and making the distance from the pipe wall to the fish relatively short and predictable.

NO20151277A1 discloses a system for grading fish while moving the fish from one place to another. The system includes at least two fish tanks for receiving the fish after the grading, means for draining off seawater and a pipe system transporting the fish.

NO314481B1 disclose a device for sorting marine objects, in particular live fish, located in a cage or the like. It has a transfer path for moving objects from a first volume of water to one of two volumes of water. A sorting grid is arranged in the transfer path. Objects under a certain size are allowed to pass the sorting grid.

To meet the demand for higher capacities in fish treatment systems, the prevailing solution has been to install multiple treatment systems/lines in parallel. Each additional line here adds a bit less than its rated capacity, as the lines can be hard to balance with flow and fish entry. Each additional line also requires a complete set of the necessary equipment for performing fish treatment, including for example, pumps, sensors, electronics, and piping, and consequently also comes with the associated costs and space requirements. Connecting multiple treatment lines to larger diameter pipes is especially problematic as it requires splitting of the flow and additional handling. The latter is known in the art to increase the risk of injuries inflicted on the fish and to cause blockages of the system.

When the substituting the water in systems such as the ones described above, it is common to let the fish slide above a grid or bars located in an atmosphere of air to drain the water through the grid before reintroducing the fish to water. This is however stressful for the fish and there is a risk that the fish is injured in the contact with the grid. Such systems are furthermore not well suited for different geometries.

The present invention aims to provide an alternative to the above-mentioned solutions for how to continuously exchange the water in ducts or channels with flowing water or to sort fish between ducts or channels at a large scale with consistent results.

The present invention also aims to provide a component or module that is adapted to be used in a complete fish treatment system with a water duct with a substantially rectangular cross-section in a plane perpendicular to the main component of the direction of flow.

The present invention thus relates to a fish transport apparatus for utilising a graded water flow transition between different water flows in a water channel for fish. The water channel comprises one upstream portion, at least one downstream portion and an inner water channel wall. The apparatus is thus adapted to move fish in an upstream mass flow of water of a first quality in the upstream portion, in a direction towards the at least one downstream portion, and the apparatus is adapted to move fish from the upstream portion to the downstream portion, A first flow port in the inner channel wall is located between the upstream portion and the at least one downstream portion and includes a first flow port area including a first flow port length L1 and a first flow port grid for a first mass flow of water. A second flow port is located in the inner channel wall between the upstream portion and the at least one downstream portion, with a second flow port area including a second flow port length L2 and a second flow port grid for a second mass flow of water in the channel inner wall. At least a portion of the first flow port area is facing the second flow port area. At least one of the upstream portion, the downstream portion, the second flow port and the first flow port is/are in fluid communication with a water mass flow control device. The water mass flow control device is adapted to ensure that a portion of the first mass flow of water exits the first flow port. The water mass flow control device is adapted to ensure that a portion of the second mass flow of water flows through the at least one downstream portion. A distance H1 between the first flow port and the second flow port and the first flow port length L1 and the second flow port length L2 are adapted to allow a graded water flow transition with a graded water flow angle α of less than 45° in relation to a longitudinal axis of the water channel.

The water channel may have a rectangular cross-section with a height H2 and a width W, and the height of the upstream portion of the water channel may be adapted to the size of a fish to be transported to prevent fish from being located above or below each other.

The water channel may have a rectangular cross-section with a height H2 and a width W, and the width of the upstream portion of the water channel may be adapted to the size of a fish to be transported to prevent fish from being located next each other.

The water mass flow control device may be adapted to control the mass flow of at least one of the upstream mass flow of water, the first mass flow of water and a second mass flow of water through the second flow port.

The first flow port may be adapted to provide a first mass flow of water of a second quality different from the upstream mass flow of water of the first quality in the upstream portion.

The first flow port may be adapted to provide a first mass flow of water greater than the upstream mass flow of water, and the second flow port may be adapted to drain away a mass flow of water greater than the upstream mass flow of water.

The fish transport apparatus may further include a sorting grid with a big fish side and a first downstream portion for big fish and a small fish side and a second downstream portion for small fish and an opening adapted to allow small fish to escape through while big fish is prevented from being allowed to escape through, and wherein the first downstream portion forms a water channel different from a water channel formed by the second downstream portion.

The first downstream portion may form a water channel different from a water channel formed by a second downstream portion and the water mass flow control device may be adapted to control the first mass flow of water and the second mass flow of water through the second flow port to allow one of said mass flows of water to enter through a flow port while the other of said mass flows of water to exit through a flow port, forming a direction of flow, whereby the water mass flow control device is adapted to change said direction of flow, and whereby the fish transport apparatus is adapted to control whether a fish exits through the first downstream portion or the second downstream portion.

Furthermore, the invention relates to method of exchanging the water in a fish transport apparatus as described above. The method comprises the steps of providing water and fish at an upstream mass flow of water through the upstream portion of the water channel A first mass flow of water is provided from the channel wall first flow port. A second mass flow of water is drained from the channel wall second flow port, wherein the upstream mass flow of water is smaller than the second mass flow of water. The upstream mass flow of water, the first mass flow of water and the second mass flow of water is balanced to provide a graded water flow transition between the upstream mass flow of water and the first mass flow of water with a graded water flow angle α of less than 45° in relation to a longitudinal axis of the water channel.

Furthermore, the invention relates to method of sorting fish in a fish transport apparatus as described above including providing a control input to the water mass flow control device indicating whether a fish should be sorted to the first downstream portion or the second downstream portion, providing a mass flow of water to one of the first flow port and the second flow port, and removing a mass flow of water from the other of the first flow port and the second flow port to selectively move the fish to exit either through the first downstream portion or the second downstream portion.

Short description of the enclosed figures:

Fig 1 is a schematic representation of a fish-farming fish transport apparatus of an embodiment of the invention;

Fig. 2 is a perspective view of a cross-section of a fish-farming fish transport apparatus shown in fig. 1;

Fig. 3 is a perspective view, partly with phantom lines of the embodiment of the invention as shown in figs. 1 and 2;

Fig. 4 shows a fish-farming fish transport apparatus in a second embodiment;

Fig. 5 is a perspective view of a cross-section of the fish-farming fish transport apparatus shown in fig. 4;

Fig. 6 is a perspective view partly with phantom lines, showing the embodiment of the invention as shown in figs. 4 and 5;

Fig. 7 is a perspective view of a cross-section of yet a further embodiment of a fishfarming fish transport apparatus, partly shown in fig.5;

Fig. 8 is a perspective view partly with phantom lines, of the embodiment of the invention as shown in fig. 7; and

Fig. 9 is a schematic representation of a modular pipe system for delousing fish with a fish transport apparatus of the invention.

Detailed description of embodiments of the invention with reference to the enclosed figures:

Fig 1 is a schematic representation of a fish-farming fish transport apparatus (1) of an embodiment of the invention with a water exchanger 1. A water channel 2 for fish 20 includes an upstream portion3, a downstream portion 4 and a channel inner wall 16. The device is adapted to move the fish 20 in a direction towards the downstream portion 4. A first flow port 9 with a first flow port area 17 and a second flow port grid 21 is provided for a upstream mass flow 11 of water of a first water quality from the upstream portion 3 in the channel inner wall 16. A second flow port 10 with a second flow port area 18 for a second mass flow of water 13 of a second water quality is also located in the channel inner wall 16. At least a portion of the first flow port area 17 is facing the second flow port area 18 such that the first flow port area 17 and the second flow port area 18 are opposing and opposite to each other and overlapping. The location of the first flow port area 17 in relation to the second flow port area 18 allows the upstream mass flow 11 of water of a first water quality to exit from the water channel 2 while at the same time, the second mass flow of water 13 of a second water quality replenishes and substitutes the upstream mass flow 11. A portion of excess water 12 from the second flow port 10 flows directly to the first flow port 9 to ensure that none of the upstream mass flow 11 of water of the first water quality is mixed with the second mass flow of water 13. This is important to prevent unwanted elements in the upstream mass flow 11 to continue to the downstream mass flow 13. Unwanted elements may include parasites such as salmon lice, chemicals or medicaments for treating the fish, faeces, fodder, water with the wrong temperature, water low on oxygen, water of wrong salinity etc.

Either or several of the upstream portion, the downstream portion, the second flow port and the first flow port is/are in fluid communication with a water mass flow control device to control and balance the flows to ensure that the two flows do not mix or to achieve a controlled the mix. The upstream mass flow 11 is typically equal to or smaller than the downstream mass flow 13. The upstream mass flow 11 preferably equal to the downstream mass flow 13 The fish transport apparatus 1 with a water exchanger is preferably completely filled with water with no air present inside the channel.

The water mass flow control device ensures that a major portion of the first mass flow of water 11 of the first water quality exits the channel wall first flow port. The water mass flow control device is adapted to ensure that a major portion of the downstream mass flow 13 of water of the second water quality flows through the downstream portion 4. The water mass flow control device is typically a water pump. If a source of flowing water is available, then the water mass flow control device may be some sort of flow control valve. Water may be taken from the second distribution chamber first flow port 15 and may be pumped through a water treatment system and may then be reintroduced through the first distribution chamber second flow port 14. The water treatment system may include filters, aeration elements, UV treatment systems, heating or cooling elements etc.

The first distribution chamber 8 with the distribution cavity 7 distributes water over the second flow port area 18 of the channel wall second flow port 10. Similarly, is water allowed to exit through the second distribution chamber 6 with the second distribution chamber cavity 7 collecting water over the first flow port area 17 of the channel wall first flow port 9. The location og the second flow port area 18 and the first flow port area 17 in addition to the water flows, produces an inclined transition between the first mass flow of water 11 and the second mass flow of water 13 with an angle α. The angle α can be controlled by controlling the flows of water through the water channel and through the channel wall second flow port 10 and the channel wall first flow port 9. Furthermore, is the angle α of the inclined transition / the graded water flow transition 30 between the first mass flow of water 11 and the second mass flow of water 13 affected by the dimensions of the second flow port area 18 and the first flow port area 17 and the position of these areas in relation to each other. These dimensions are explained further in connection with fig. 7. In fig 1. are these areas equal and located directly opposite of each other, i.e. located at the same location in relation to a longitudinal axis of the water channel 2. A longer second flow port and first flow port area in the direction of the longitudinal axis of the water channel 2 will produce a more acute angle α. The angle α of the graded water flow transition 30 between the first mass flow of water 11 and the second mass flow of water 13 should be less than 45° to prevent the fish from being pushed towards the grid 17 where water exits the water channel. A second mass flow of water 31 flows into or out of the second distribution chamber 6.

All the grids that are in contact with the fish are designed to be gentle for the fish to prevent harming the fish.

Fig. 2 is a perspective view of a cross-section of a fish-farming fish transport apparatus 1 with a water exchanger as schematically shown in fig. 1. The water channel 2 has a rectangular cross-section with the upstream portion and the downstream portion 4. The first mass flow of water 11 is indicated with an arrow at the upstream portion and the second mass flow of water 13 is indicated with an arrow at the downstream portion 4. The height of the water channel 2 is adapted to the height of the fish 20 to distribute fish 20 in one layer, i.e. that fish should be prevented from being located above each other. A first flow port grid 19 between the first distribution chamber cavity 7 and the water channel 2 may be formed as longitudinal slots or bars in the lengthwise direction of the water channel 2. The flow port grids may also be formed with rolls or in any other way that is gentle to the fish. The bars or slots in the channel inner wall 16 ensure that the fish 20 not enters into the first distribution chamber 7 or the second distribution chamber 5. The bars or slots forming the first flow port grid 19 and the second flow port grid 21 may be slots cut out in the inner wall 16 or may be a separate grid that may be assembled of individual bars. The first distribution chamber second flow port and the second distribution chamber first flow port are not shown.

Fig. 3 is a perspective view, partly with phantom lines, showing the embodiment of the invention as shown in figs. 1 and 2. The fish transport apparatus 1 with a water exchanger is formed as a module or component that may be installed in a complete fish handling system with other modules, typically for delousing, measuring the fish, visual control of the fish with cameras, etc. The first flow port grid has a first flow port area 17 above the first distribution chamber cavity 7 defined by the width of the water channel 2 and the length of the first flow port grid. The length of the first flow port grid is important for the flow conditions inside the fish transport apparatus 1 with a water exchanger as shown in fig. 1. The first distribution chamber first flow port and the second distribution chamber first flow port are not shown.

Fig. 4 shows a fish-farming fish transport apparatus 1 of a second embodiment for sorting fish. In this embodiment are fish sorted between big fish 20a allowed to be transported through a first downstream portion 4a and sorted between smaller fish 20b allowed to be transported through a second downstream portion 4b. A sorting grid 22 with longitudinal bars lets the small fish 20b through while the big fish 20a is too big to move between the bars. The first mass flow of water through the upstream portion 3 flows through the sorting grid 22 and is pressed into the second distribution chamber 6 and out of the second distribution chamber second flow port 15 by the second mass flow of water entering through the first distribution chamber second flow port 14 and flowing into the first downstream portion 4a and the second downstream portion 4b. Again, the inclined transition between the first mass flow of water and the second mass flow of water with an angle α is indicated by dotted lines.

Fig. 5 is a perspective view of a cross-section of a fish-farming fish transport apparatus 1 as schematically shown in fig. 4. The water channel 2 has a rectangular cross-section with the upstream portion and the first downstream portion 4a for big fish 20a, and the second downstream portion 4b for smaller fish 20b. The first mass flow of water 11 is indicated with an arrow at the upstream portion. The distance between the bars of the sorting grid 22 allows the smaller fish 20b to enter the second downstream portion 4b forming a separate channel to a separate habitat for the smaller fish. An inclined guiding portion 23 serves to guide the small fish out through the second downstream portion 4b, and to lead the water flow inside the exchanger.

Fig. 6 is a perspective view partly with phantom lines, shows the embodiment of the invention as shown in figs. 4 and 5. The fish-farming fish transport apparatus 1 includes a sorting grid 22 allowing big fish to exit through the first downstream portion 4a and smaller fish to exit through the second downstream portion 4b. The water flow from the upstream portion of the water channel and out through the second flow port grid of the second distribution chamber positions the fish towards the first flow port, and the smaller fish thus exit through the sorting grid 22.

Fig. 7 is a perspective view of a cross-section of yet a further embodiment of a fishfarming fish transport apparatus 1, partly as schematically shown in fig.5. In fig 6 is however the sorting grid 22 shown in fig 5 omitted. The fish 20 is sorted between the first downstream portion 4a, and the second downstream portion 4b by altering the flow conditions. In the solution of fig. 7, may the direction of flow between the second distribution chamber cavity 5 and the first distribution chamber cavity 7 be altered and the location of the fish 20 may thus be controlled. The first distribution chamber second flow port and the second distribution chamber first flow port are not shown. A height H2 of the upstream portion may be adapted a height of the fish to prevent fish from entering the portion between the grids above each other. The distance H1 between the channel wall first flow port 9 and the channel wall second flow port 10 and their position opposite each other in combination of the length L1 of the channel wall first flow port 9 and the length L2 of the channel wall second flow port 10 are adapted to form the graded water flow transition shown in fig. 1. In the embodiment for exchanging water shown in figures 1-3 is the distances H1 and the height H2 equal. In the embodiments for sorting fish is the distance H1 between channel wall first flow port 9 and the channel wall second flow port 10 greater than the height H2 of the upstream portion. The length L1, L2 of the channel wall flow ports 9, 10 allows the water to be exchanged over a length inside the water channel 2. The width W of the channel wall flow ports 9, 10 and the length L1, L2 of the channel wall flow ports define the flow port areas 17, 18. The mass flow of the water flowing through the flow port areas should preferably be even over the area.

Fig. 8 is a perspective view partly with phantom lines, shows the embodiment of the invention as shown in fig. 7. The fish-farming fish transport apparatus 1 includes a flow control sorting arrangement allowing fish of choice to exit through the first downstream m portion 4a and fish of choice to exit through the second downstream portion 4b. The water flow from positions the fish as required in the cross-section. A water mass flow control device controls the water to exit one of the second flow port grid and the first flow port grid to control the fish and the flow control device controls the direction of the water flow.

Fig. 9 schematically illustrates a modular pipe system 30 for delousing fish where the modular pipe system 30 includes a fish-farming water exchange device 1 as a module in the modular pipe system 30 for delousing fish. The modular pipe system 30 is further illustrated including a first coupling unit 25 for connecting a first end of the modular pipe system 30 to a circular pipe, and a second coupling unit 26 for connecting a second end of the modular pipe system 30 to a circular pipe. The first coupling unit 25 is configured to connect a first end of modular pipe system with a circular pipe, typically a pipe with a diameter of 250mm commonly used in connection with fish-farming. The first and the second coupling units, 25, 26 forms a transition between the circular cross-section of the pipes and the rectangular cross-section 2 of the modules including the fish transport apparatus 1 formed as a water exchange module.

The modular pipe system 30 may as schematically illustrated in fig. 9 includes additional modules 24, such as auxiliary modules for treatment or handling of fish imaging modules for imaging fish. The modular pipe system 30 establishes a fluid pathway through the entire system 30, i.e. from a circular pipe into the first coupling unit 25, through the modules 1, 24 of the modular system 30, and out through the second coupling unit 26 into another circular pipe.

The flow control device 27 allows control of the water into and out of the channel wall flow ports and may control valves and/or pumps and may also control the first flow of water through the upstream water portion and a back pressure in the at least one downstream portion. The flow control device may receive input from various sensors relating to waterflows, fish count, water quality, etc.

The flow control device 27 should thus be able to control the waterflows / water velocities in and out of the system, the water velocity internally in the apparatus, the density of the fish in the system and a treatment volume of the system.

The fish transport apparatus of the invention may be used to prevent and solve congestions of fish, optimize treatment of fish by ensuring the ideal density and speed of the of fish, potentially increase the capacity of a system, and to differentiate the water velocity during transport and treatment to enable higher fish velocities. These effects can be achieved by manipulating the amount of water in the cross-section as the invention enables supply or draining of water at the end of the apparatus or along a system where the invention is utilized.

The fish transport apparatus may be configured to adjust the velocity of water in the range from 1.5 m/s to 2.5 m/s. A module with the fish transport apparatus may be positioned downstream from a delousing module in a delousing. This velocity has been found to be optimal for maintaining the welfare of the fish, while at the same time enabling removal of sea lice from the skin of the fish.

In the above description are the terms second distribution chamber, first distribution chamber, second flow port area, first flow port area, channel wall second flow port, channel wall first flow port, etc. used to simplify the description and to explain the operation of the invention. In some situations, the direction of flow is altered, and role of the various components and features will then be the opposite of what is described. In such situations will what is described as the second flow port be the first flow port, what is described as the first flow port will be the inlet, what is described as the second distribution chamber will be the first distribution chamber, what is described as the first distribution chamber will be the second distribution chamber etc.

Two or more fish transport apparatuses for utilising a graded water flow transition between different water flows as described above may be installed, one after the other to provide a water lock system or to combine water exchange and fish sorting in the event the water is not sufficiently exchanged in a first step. Such systems may be used to make a section using water with “particular properties” to treat the fish.

“Particular properties” may include water with medicaments, a different temperature, different salinity, chemicals etc.

The suction of the fish towards the grids is reduced due to the water transition gradient. The suction is towards the abdomen / bottom of the fish to minimize the risk of suction towards the side of the fish where the surface area of the fish is much greater, thus increasing the risk that the fish contacts the grid and gets stuck.

The width of the channel may be restricted to only one fish for better control and for predictable analysis and treatment of each individual fish.

1 Water exchanger 23 Inclined guiding portion 2 Water channel 24 Additional module

3 Upstream portion 25 First coupling unit

4 downstream portion 26 Second coupling unit

4a First downstream portion 27 Water mass flow control device 4b Second downstream portion 28 Water connection

5 Second distribution chamber cavity 29 Water supply

6 Second distribution chamber 30 Graded water flow transition 7 First distribution chamber cavity 31 Second mass flow of water 8 First distribution chamber

9 Channel wall first flow port

10 Channel wall second flow port

11 Upstream mass flow of water

12 First mass flow of water

13 Downstream mass flow of water

14 First distribution chamber second

port

15 Second distribution chamber second

port

16 Channel inner wall

17 Second flow port area

18 First flow port area

19 First flow port grid

20 Fish

20a Big fish

20b Small fish

21 Second flow port grid

22 Sorting grid

Claims (10)

1. A fish transport apparatus (1) for utilising a graded water flow transition between different water flows in a water channel (2) for fish, the water channel comprising:

one upstream portion (3), at least one downstream portion (4) and an inner water channel wall (16) whereby the apparatus is adapted to move fish in an upstream mass flow of water (11) of a first quality in the upstream portion, in a direction towards the at least one downstream portion (4), and whereby the apparatus is adapted to move fish from the upstream portion (3) to the downstream portion (4);

a first flow port (9) in the inner channel wall (16) between the upstream portion (3) and the at least one downstream portion (4), with a first flow port area (18) including a first flow port length L1 and a first flow port grid (19) for a first mass flow of water (12);

a second flow port (10) in the inner channel wall (16) between the upstream portion (3) and the at least one downstream portion (4), with a second flow port area (17) including a second flow port length L2 and a second flow port grid (21) for a second mass flow of water in the channel inner wall (16);

wherein at least a portion of the first flow port area (18) is facing the second flow port area (17);

at least one of the upstream portion (3), the downstream portion (4), the second flow port (10) and the first flow port (9) is/are in fluid communication with a water mass flow control device (27);

wherein the water mass flow control device (27) is adapted to ensure that a portion of the first mass flow of water exits the first flow port (9);

wherein the water mass flow control device (27) is adapted to ensure that a portion of the second mass flow of water flows through the at least one downstream portion (4); and

wherein a distance H1 between the first flow port (9) and the second flow port (10) and the first flow port length L1 and the second flow port length L2 are adapted to allow a graded water flow transition (30) with a graded water flow angle α of less than 45° in relation to a longitudinal axis of the water channel (2).

2. The fish transport apparatus of clam 1, wherein the water channel (2) has a rectangular cross-section with a height H2 and a width W; and

wherein the height of the upstream portion (3) of the water channel (2) is adapted to the size of a fish (20) to be transported to prevent fish (20) from being located above or below each other.

3. The fish transport apparatus of clam 1, wherein the water channel (2) has a rectangular cross-section with a height H2 and a width W; and

wherein the width of the upstream portion (3) of the water channel (2) is adapted to the size of a fish (20) to be transported to prevent fish (20) from being located next each other.

4. The fish transport apparatus (1) of one of the preceding claims, wherein the water mass flow control device (27) is adapted to control the mass flow of at least one of the upstream mass flow of water (11), the first mass flow of water (12) and a second mass flow of water through the second flow port (9).

5. The fish transport apparatus (1) of any of the preceding claims, wherein the first flow port (9) is adapted to provide a first mass flow of water (12) of a second quality different from the upstream mass flow of water (11) of the first quality in the upstream portion (3).

6. The fish transport apparatus (1) of any of the preceding claims wherein the first flow port (9) is adapted to provide a first mass flow of water (12) greater than the upstream mass flow of water (11), and wherein the second flow port is adapted to drain away a mass flow of water greater than the upstream mass flow of water (11).

7. The fish transport apparatus (1) of any of the preceding claims, further including a sorting grid (22) with a big fish side and a first downstream portion (4a) for big fish (20a) and a small fish side and a second downstream portion (4b) for small fish (20b) and an opening adapted to allow small fish (20b) to escape through while big fish (20a) is prevented from being allowed to escape through; and

wherein the first downstream portion (4a) forms a water channel different from a water channel formed by the second downstream portion (4b).

8. The fish transport apparatus (1) claim 4, wherein a first downstream portion (4a) forms a water channel different from a water channel formed by a second downstream portion (4b), and wherein the water mass flow control device (27) is adapted to control the first mass flow of water (12) and the second mass flow of water through the second flow port (9) to allow one of said mass flows of water to enter through a flow port while the other of said mass flows of water to exit through a flow port, forming a direction of flow, whereby the water mass flow control device (27) is adapted to change said direction of flow, and whereby the fish transport apparatus (1) is adapted to control whether a fish exits through the first downstream portion (4a) or the second downstream portion (4b).

9. A method of exchanging the water in a fish transport apparatus of any of the preceding claims comprising the steps of:

providing water and fish at an upstream mass flow of water (11) through the upstream portion (3) of the water channel (2);

providing a first mass flow of water (12) from the channel wall first flow port (9); draining a second mass flow of water (31) from the channel wall second flow port (10), wherein the upstream mass flow of water (11) is smaller than the second mass flow of water (31); and

wherein the upstream mass flow of water (11), the first mass flow of water (12) and the second mass flow of water (31) is balanced to provide a

a graded water flow transition (30) between the upstream mass flow of water (11) and the first mass flow of water (12) with a graded water flow angle α of less than 45° in relation to a longitudinal axis of the water channel (2).

10. A method of sorting fish in a fish transport apparatus of claim 8 comprising the steps of:

providing a control input to the water mass flow control device (27) indicating whether a fish (20) should be sorted to the first downstream portion (4a) or the second downstream portion (4b);

providing a mass flow of water to one of the first flow port (9) and the second flow port (10); and

removing a mass flow of water from the other of the first flow port (9) and the second flow port (10) to selectively move the fish (20) to exit either through the first downstream portion (4a) or the second downstream portion (4b).