JP7558499B2 - Water exchange device, water exchange method, and marine fish production method - Google Patents

Description

The present invention relates to a water exchange device, a water exchange method, and a method for producing marine fish.

It is known that rearing saltwater fish in water with a lower salinity than seawater can extend the lifespan of the fish and allow them to recover from injuries (Patent Document 1). Patent Document 2 discloses a method for preserving saltwater fish that promotes recovery from injuries while suppressing weight loss.

When breeding saltwater fish, it is necessary to replace the breeding water in order to remove contaminants derived from the saltwater fish. The process of replacing the breeding water is also called "water exchange." In order to prepare breeding water with a lower salinity than seawater as described above, for example, a mixing tank for mixing seawater and freshwater can be provided separately from the breeding tank, and the salt concentration can be adjusted to a predetermined level in the mixing tank (Patent Document 3).

Patent No. 5803026 Patent No. 6733095 JP 2018-130080 A

However, to implement the methods described in Patent Document 1 or Patent Document 2, a mixing layer is required to mix seawater and freshwater in order to prepare rearing water with a low salinity, as disclosed in Patent Document 3. This makes it difficult to miniaturize the water exchange device.

One aspect of the present invention aims to realize a water exchange device that can easily perform water exchange while maintaining the salinity of the rearing water within a predetermined range without providing a mixing layer.

In order to solve the above problems, a water exchange device according to one embodiment of the present invention includes a first water inlet that supplies high-salinity water, the salinity of which is equal to or greater than the upper limit of the predetermined range, to an aquarium that contains breeding water for breeding saltwater fish, the salinity of which is within a predetermined range; a second water inlet that supplies low-salinity water, the salinity of which is equal to or less than the lower limit of the predetermined range, to the aquarium; and a water level detection unit that detects the water level in the aquarium in order to calculate the amount of water supplied from the first water inlet, the amount of water supplied from the second water inlet, and the amount of water discharged from the aquarium.

According to the above configuration, since the water exchange device has a first water inlet and a second water inlet, by connecting these first water inlet and second water inlet to the rearing aquarium, the salinity of the rearing water can be kept within a predetermined range without providing a mixing tank for mixing high-salinity water and low-salinity water separately from the aquarium that contains the rearing water. Therefore, the entire rearing system configuration including the water exchange device and the aquarium can be made compact.

In addition, since the water exchange device is equipped with a water level detection unit, the amount of water supplied from the first water supply port, the amount of water supplied from the second water supply port, and the amount of water discharged from the aquarium can be controlled based on a prediction of the salinity concentration of the rearing water. This reduces the frequency of monitoring the salinity concentration of the rearing water. Therefore, water exchange can be easily performed while maintaining the salinity concentration of the rearing water within a predetermined range.

The water exchange device according to one aspect of the present invention may further include a water supply switching unit that switches between water supply from the first water supply port and water supply from the second water supply port. According to the above configuration, the water supply switching unit switches between water supply from the first water supply port and water supply from the second water supply port, so that water is supplied from either the first water supply port or the second water supply port. Therefore, even if the raw water pressure of the first water supply port and the second water supply port fluctuates, the water level detection unit can more accurately control the amount of water supplied from the first water supply port and the amount of water supplied from the second water supply port. This makes it possible to more accurately predict the salinity of the rearing water and reduce the frequency of monitoring the salinity of the rearing water. Therefore, water exchange can be performed more easily while maintaining the salinity of the rearing water within a predetermined range.

In addition, in the water exchange device according to one aspect of the present invention, the drainage rate from the water tank may be greater than at least one of the water supply rate from the first water supply port and the water supply rate from the second water supply port.

With the above configuration, the drainage speed is faster than the water supply speed, so the amount of high-salinity water or low-salinity water that is not mixed with the breeding water and is drained directly from the aquarium can be reduced. This makes it possible to efficiently remove pollutants derived from saltwater fish.

In addition, the salinity of the rearing water in the aquarium can be predicted more accurately, reducing the frequency of monitoring the salinity of the rearing water. This makes it easier to change the water while keeping the salinity of the rearing water within a specified range.

The water exchange method according to one aspect of the present invention includes a first step of performing each of the following substeps at least once: (1) a first drainage substep, (2) a first water supply substep, and (3) a first homogenization substep performed after the first drainage substep and the first water supply substep.

(1) First drainage sub-step: draining water for breeding saltwater fish from the aquarium;
(2) a first water supply sub-step: supplying water having a first salinity to the aquarium, the first salinity being set by selecting a value equal to or greater than an upper limit value of the predetermined range or a value equal to or less than a lower limit value of the predetermined range, so that the salinity of the rearing water after the first homogenization sub-step falls within a predetermined range;
(3) First homogenization sub-step: homogenizing the salinity concentration of the breeding water in the aquarium.

According to the above method, the salinity of the rearing water in the aquarium is homogenized in the first homogenization sub-step, so that the salinity of the rearing water in the aquarium can be predicted with high accuracy even after the first step. This reduces the frequency of monitoring the salinity of the rearing water. This makes it possible to easily perform water changes while maintaining the salinity of the rearing water within a predetermined range.

The water exchange method according to one aspect of the present invention may also include a second step, after the first step, of performing each of the following substeps, (4) a second drainage substep, (5) a second water supply substep, and (6) a second homogenization substep performed after the second drainage substep and the second water supply substep, at least once.

(4) A second drainage sub-step: draining the water for breeding saltwater fish from the aquarium;
(5) Second water supply sub-step: supplying water of a second salinity to the aquarium, the second salinity being set to be equal to or less than the lower limit if the first salinity is equal to or more than the upper limit if the first salinity is equal to or less than the lower limit, so that the salinity of the rearing water after the second homogenization sub-step falls within a predetermined range;
(6) Second homogenization sub-step: homogenizing the salinity concentration of the breeding water in the aquarium.

According to the above method, when the first salinity is equal to or greater than the upper limit, the second salinity is set equal to or less than the lower limit, so that the salinity of the rearing water can be increased in the first step and decreased in the second step. Therefore, by repeating the first and second steps, the salinity of the rearing water can be maintained within a predetermined range for a long period of time.

In addition, when the first salinity concentration is equal to or lower than the lower limit, the second salinity concentration is set to equal to or higher than the upper limit, so that the salinity concentration of the rearing water can be reduced in the first step and increased in the second step. Therefore, by repeating the first and second steps, the salinity of the rearing water can be maintained within a predetermined range for a long period of time.

In addition, in the water exchange method according to one aspect of the present invention, if the predicted salinity of the rearing water after the most recent first homogenization sub-step is within the predetermined range, and the predicted salinity of the rearing water when the next first drainage sub-step, first water supply sub-step, and first homogenization sub-step are performed will be outside the predetermined range, the next first drainage sub-step, first water supply sub-step, and first homogenization sub-step may not be performed.

According to the above method, the first step can be terminated just before the predicted salinity of the rearing water after repeating the first drainage sub-step, the first water supply sub-step, and the first homogenization sub-step falls outside the predetermined range. Therefore, the salinity of the rearing water can be maintained within the predetermined range for a longer period of time while performing water changes.

In addition, a method for producing saltwater fish according to one embodiment of the present invention is to raise the fish in an aquarium in which the salinity of rearing water is adjusted by a water exchange method including a first step of carrying out each of the following substeps at least once: (1) a first drainage substep, (2) a first water supply substep, and (3) a first homogenization substep carried out after the first drainage substep and the first water supply substep.

(1) First drainage sub-step: draining water for breeding saltwater fish from the aquarium;
(2) a first water supply sub-step: supplying water having a first salinity to the aquarium, the first salinity being set by selecting a value equal to or greater than an upper limit value of the predetermined range or a value equal to or less than a lower limit value of the predetermined range, so that the salinity of the rearing water after the first homogenization sub-step falls within a predetermined range;
(3) First homogenization sub-step: homogenizing the salinity concentration of the breeding water in the aquarium.

According to one aspect of the present invention, it is possible to realize a water exchange device that can easily perform water exchange while maintaining the salinity of the rearing water within a predetermined range without providing a mixing layer.

FIG. 1 is a schematic diagram showing a breeding system according to an embodiment. 1 is a flowchart illustrating a water exchange method according to one embodiment. 1 is a graph showing predicted results of salinity when low-salinity water is used in a water exchange method according to one embodiment. 1 is a graph showing predicted results of salinity when high-salinity water is used in a water exchange method according to one embodiment. 1 is a graph showing predicted results of salinity when low-salinity water and high-salinity water are alternately used in a water exchange method according to one embodiment. 1 is a graph showing a simulation result of a transition of a concentration of persistent organic matter by a water exchange method according to one embodiment. 1 is a graph showing the change in salinity concentration due to the water exchange method of Example 1. 1 is a graph showing the evaluation results of saltwater fish produced using the water exchange method of Example 1.

[Breeding system]
An embodiment of the present invention will be described in detail below. Fig. 1 is a schematic diagram showing a breeding system 1 according to this embodiment. The breeding system 1 is a breeding system for breeding saltwater fish. As shown in Fig. 1, the breeding system 1 includes a water exchange device 100, a breeding aquarium (aquarium) 8, a biological filtration tank 9, a circulation pump 6, a heating and cooling unit 5, and a control panel 4. In Fig. 1, solid arrows represent the flow path of the breeding water, and dashed arrows represent electrical signals.

In this embodiment, the breeding system 1 is a closed circulation system that filters and recycles breeding water 26 for breeding saltwater fish, and part of the breeding water 26 is replaced by water exchange.

The breeding tank 8 contains breeding water 26 with a salt concentration in a predetermined range CR for breeding saltwater fish. Here, the predetermined range CR of the salt concentration can be appropriately selected according to the species of saltwater fish or the breeding purpose. In order to improve the effect of extending the life of saltwater fish and recovering from trauma, the upper limit value Cmax related to the predetermined range CR is preferably 2.7% or more and 3.0% or less, and the lower limit value Cmin related to the predetermined range CR is preferably 0.55% or more and 1.4% or less. More specifically, as disclosed in Patent Document 1, in order to improve the effect of extending the life of saltwater fish and recovering from trauma, the upper limit value Cmax is preferably 2.75% and the lower limit value Cmin is preferably 0.55%. Also, as disclosed in Patent Document 2, in order to promote the recovery of saltwater fish from trauma while suppressing weight loss, the upper limit value Cmax is preferably 3.0% and the lower limit value Cmin is preferably 0.9%. The breeding tank 8 is provided with a drainage valve 12 to control the drainage of the breeding water 26.

An air stone 10 is provided near the bottom inside the breeding tank 8. The air stone 10 is connected to the blower 2 via an air tube 20. The air stone 10 and the blower 2 are configured so that the air supplied from the blower 2 is released as air bubbles from the air stone 10, thereby supplying oxygen to the breeding water 26.

The water exchange device 100 is a device for exchanging the breeding water 26 in the breeding tank 8. The water exchange device 100 includes a first water supply port 14, a second water supply port 15, a water supply switching unit 3, a water supply valve 13, and a water level sensor (water level detection unit) 7.

The first water supply port 14 supplies high-salinity water, the salinity of which is equal to or greater than the upper limit Cmax, to the breeding tank 8. For example, seawater can be used as the high-salinity water. The second water supply port 15 supplies low-salinity water, the salinity of which is equal to or less than the lower limit Cmin, to the breeding tank 8. For example, tap water, river water, or groundwater can be used as the low-salinity water.

The water supply switching unit 3 switches between the water supply from the first water supply port 14 and the water supply from the second water supply port 15. Therefore, in this embodiment, the high salinity water supplied from the first water supply port 14 and the low salinity water supplied from the second water supply port 15 are supplied to the breeding aquarium 8 through the water supply switching unit 3. The water exchange device 100 does not need to have the water supply switching unit 3. In this case, the first water supply port 14 and the second water supply port 15 are directly connected to the aquarium 8. In this case, the water exchange device 100 may have a water supply valve that can independently control the amount of water supplied from each water supply port in each pipe leading to the first water supply port 14 and the second water supply port 15, instead of a single water supply valve 13. The opening and closing of these water supply valves may be controlled by the function of the control panel 4 described later, or may be manually controlled by the user.

The water level sensor 7 detects the water level of the breeding water 26 in the breeding tank 8. By detecting the water level of the breeding water 26, the water level sensor 7 can calculate the amount of water supplied from the first water supply port 14, the amount of water supplied from the second water supply port 15, and the amount of water discharged from the breeding tank 8.

The biological filtration tank 9 is an aquarium for containing the breeding water 27 that has overflowed from the breeding tank 8 and for biological filtration. In this embodiment, the breeding tank 8 and the biological filtration tank 9 are arranged so that the water level of the breeding water 27 in the biological filtration tank 9 is lower than the water level of the breeding water 26 in the breeding tank 8, and the breeding water 26 that has overflowed from the breeding tank 8 flows into the biological filtration tank 9. Alternatively, the breeding tank 8 and the biological filtration tank 9 may be arranged so that the water level of the breeding water 27 in the biological filtration tank 9 is higher than the water level of the breeding water 26 in the breeding tank 8, and the breeding water 27 that has overflowed from the biological filtration tank 9 flows into the breeding tank 8 (not shown).

The circulation pump 6 sends the breeding water 27 in the biological filtration tank 9 to the breeding tank 8 via the heating and cooling unit 5. Therefore, the breeding water 26 in the breeding tank 8 circulates to the breeding tank 8 through the biological filtration tank 9, the circulation pump 6, and the heating and cooling unit 5. If the breeding water 27 overflowing from the biological filtration tank 9 is arranged to flow into the breeding tank 8, the breeding water 26 is sent from the breeding tank 8 to the biological filtration tank 9 via the heating and cooling unit 5 by the circulation pump 6. Manual valves 11 are provided at multiple locations in this circulation path. The manual valves 11 are provided to facilitate individual maintenance of each pipe of the breeding system 1. The heating and cooling unit 5 heats or cools the breeding water 27 sent out by the circulation pump 6, and adjusts it to a temperature suitable for breeding saltwater fish.

The control panel 4 includes, for example, a ground fault circuit interrupter, a manual switch, a timer switch, a relay switch, a delay switch, and a display panel (none of which are shown). The control panel 4 is electrically connected to the water supply switching unit 3, the water supply valve 13, the drain valve 12, the circulation pump 6, and the heating and cooling unit 5, and is configured to control these.

The control panel 4 is also electrically connected to the water level sensor 7, and is configured to control the water supply switching unit 3, the water supply valve 13, and the drain valve 12 according to the water level of the breeding water 26 in the breeding tank 8 detected by the water level sensor 7. The control panel 4 may also be configured to be able to control the manual valve 11. The control panel 4 may also be a control unit such as a CPU (Central Processor Unit) for overall control of the breeding system 1.

<Modification>
The water exchange apparatus 100 may be provided with a ball tap (not shown) and a rising pipe (not shown) as a water level detection unit instead of the water level sensor 7. In this case, when water is supplied to the breeding aquarium 8 from the first water supply port 14 or the second water supply port 15, the ball tap functions as the water level detection unit, and when water is discharged from the breeding aquarium 8, the rising pipe functions as the water level detection unit. In this way, the water exchange apparatus 100 may be provided with multiple water level detection units.

In this modified example, before the water level of the breeding water 26 in the breeding tank 8 falls below a predetermined lower limit, water supply is started from the first water supply port 14 or the second water supply port 15 through the water supply switching unit 3. Then, when the water level of the breeding water 26 reaches the predetermined lower limit, drainage is stopped by the rising pipe, and then the drain valve 12 is closed by the control panel 4. Then, when the water level of the breeding water 26 in the breeding tank 8 reaches a predetermined upper limit, water supply from the first water supply port 14 or the second water supply port 15 is stopped by the ball tap. Therefore, when the water exchange device 100 is equipped with a ball tap and a rising pipe, the water supply valve 13 can be omitted. When the water supply valve 13 is omitted, the drainage speed must be sufficiently greater than the water supply speed so that the error in the salinity prediction described below does not become large. In this case, for example, it is preferable that the water supply speed is less than 20% of the drainage speed.

In addition, in order to better maintain the water quality of the breeding water 26, the breeding system 1 may be equipped with, in addition to or instead of the biological filtration tank 9, a physical filtration unit, a solid-liquid separation unit such as a foam separator, or a sterilization device such as an ultraviolet device (none of which are shown).

In addition, when the amount of dissolved oxygen in the biological filtration tank 9 decreases and the function of nitrifying ammonia decreases, it is preferable for the breeding system 1 to supply air from the blower 2 to the biological filtration tank 9 in order to better maintain the water quality of the breeding water 26.

[Water exchange method]
Fig. 2 is a flow chart showing a water exchange method according to an embodiment of the present invention. In the following description, a water exchange method using the breeding system 1 shown in Fig. 1 will be described as an example, but the present invention is not limited to this, and breeding systems of other configurations may be used. In addition, the following shows an example in which a user of the breeding system 1 (hereinafter simply referred to as "user") executes each process by operating the control panel 4, etc., and some processes are executed autonomously by the functions of the control panel 4. However, which processes the control panel 4 executes autonomously is not limited to the following example.

As shown in FIG. 2, when starting the water change method, the user first predicts the salinity concentration and sets the water change period (S1). The method of predicting the salinity concentration and the method of setting the water change period will be described later. Note that the step S1 may be omitted, for example, when previously set conditions are used. Next, the user starts the first step S10. In the first step S10, the control panel 4 performs each of the following (1) first drainage sub-step S11, (2) first water supply sub-step S12, and (3) first equalization sub-step S13 at least once.

(1) First drainage sub-step S11: Drain the breeding water 26 for breeding saltwater fish from the breeding tank 8.

(2) First water supply sub-step S12: Water with a first salinity concentration set by selecting from the upper limit Cmax or higher or the lower limit Cmin or lower is supplied to the breeding aquarium tank 8 so that the salinity of the breeding water 26 after the first homogenization sub-step S13 is within a predetermined range CR.

(3) First homogenization substep S13: Homogenize the salinity of the breeding water 26 in the breeding tank 8.

The first drainage sub-step S11 is performed by opening the drainage valve 12. The control panel 4 controls the amount of drainage in the first drainage sub-step S11 according to the water level of the breeding water 26 in the breeding aquarium 8 detected by the water level sensor 7.

In the first water supply sub-step S12, the control panel 4 supplies the high-salinity water from the first water supply inlet 14 or the low-salinity water from the second water supply inlet 15 to the breeding aquarium 8 as the first salinity water. At this time, the user controls the water supply switching unit 3 to switch between the water supply from the first water supply inlet 14 and the water supply from the second water supply inlet 15 so that the salinity of the breeding water 26 after the first homogenization sub-step S13 is within the predetermined range CR. Note that if the breeding system 1 is configured without the water supply switching unit 3, the user may control the water supply valves provided at the first water supply inlet 14 and the second water supply inlet 15, respectively, instead of the water supply switching unit 3.

The control panel 4 controls the amount of water supplied in the first water supply sub-step S12 according to the water level of the breeding water 26 in the breeding aquarium 8 detected by the water level sensor 7.

The control panel 4 performs the first drainage sub-step S11, and then the first water supply sub-step S12. If the water exchange device 100 is equipped with a ball tap and a riser pipe, the control panel 4 may perform the first drainage sub-step S11 and the first water supply sub-step S12 simultaneously.

When the first drainage sub-step S11 and the first water supply sub-step S12 are performed simultaneously, it is preferable for the control panel 4 to set the drainage rate in the first drainage sub-step S11 to be greater than the water supply rate in the first water supply sub-step S12. In this case, it is possible to reduce the amount of first salinity water that is supplied and is not mixed with the breeding water 26 and is drained directly from the breeding aquarium 8. This makes it possible to efficiently remove contaminants derived from saltwater fish and to accurately estimate the salinity of the breeding water 26.

When the water exchange apparatus 100 is equipped with a ball tap and rising pipes instead of the water supply valve 13 and water level sensor 7, the first water supply sub-step S12 is started almost simultaneously with the start of the first water drainage sub-step S11. In this case, it is preferable for the control panel 4 to set the water drainage rate in the first water drainage sub-step S11 to be higher than the water supply rate in the first water supply sub-step S12. When the water drainage rate in the first water drainage sub-step S11 is higher than the water supply rate in the first water supply sub-step S12, the first water supply sub-step S12 ends after the first water drainage sub-step S11 ends.

The first homogenization sub-step S13 is performed after the first drainage sub-step S11 and the first water supply sub-step S12. The control panel 4 may perform the first homogenization sub-step S13 by, for example, waiting for a predetermined period of time with the drainage valve 12 and the water supply valve 13 closed. The control panel 4 may select the waiting period as appropriate, for example, depending on the size and shape of the breeding aquarium 8, the structure of each part of the breeding system 1, such as the breeding aquarium 8 and piping, the amount of water exchanged in the first step S10 and the second step S20, and the amount of air supplied from the blower 2. In order to ensure that the salinity of the breeding water 26 in the breeding aquarium 8 is homogenized, the control panel 4 may set the waiting period by, for example, determining in advance the period until the salinity of the breeding water 26 in the breeding aquarium 8 becomes stable when the breeding system 1 is introduced.

After the first equalization sub-step S13, the control panel 4 determines whether the set water change period has elapsed (S14). In other words, after the first equalization sub-step S13, the control panel 4 determines whether the predicted salinity of the rearing water 26 when the next first drainage sub-step S11, first water supply sub-step S12, and first equalization sub-step S13 are executed will be outside the predetermined range. Details of the setting of the water change period and the predicted salinity will be described later.

If S14 is No, the control panel 4 returns to the first drainage sub-step S11 and repeats the first drainage sub-step S11, the first water supply sub-step S12, and the first homogenization sub-step S13. On the other hand, if S14 is Yes, the control panel 4 ends the first step S10 and determines whether or not to continue raising saltwater fish (S15). In other words, if S14 is Yes, the control panel 4 does not execute the next first drainage sub-step S11, the first water supply sub-step S12, and the first homogenization sub-step S13.

In S15, the control panel 4 may determine whether or not to continue breeding saltwater fish, for example, depending on whether or not there are any saltwater fish remaining to be bred in the breeding tank 8. If the answer is Yes in S15, the user starts the second step S20. However, if the user determines that the water quality of the breeding water 26 at this point is maintained in such a good condition that water change is not necessary, the user may set a certain period of time before the second step S20 during which water change is not performed. On the other hand, if the answer is No in S15, the user ends the water change method.

In the second step S20, the control panel 4 performs each of the following sub-steps (4) second drainage sub-step S21, (5) second water supply sub-step S22, and (6) second equalization sub-step S23 at least once.

(4) Second drainage sub-step S21: Drain the breeding water 26 for breeding saltwater fish from the breeding tank 8.

(5) Second water supply sub-step S22: If the first salinity is equal to or greater than the upper limit Cmax, it is set to equal to or less than the lower limit Cmin so that the salinity of the breeding water 26 after the second homogenization sub-step S23 is within a predetermined range CR. If the first salinity is equal to or less than the lower limit Cmin, second salinity water with a second salinity set to equal to or greater than the upper limit Cmax is supplied to the breeding aquarium 8.

(6) Second homogenization sub-step S23: Homogenize the salinity of the breeding water 26 in the breeding tank 8.

The second drainage sub-step S21 is performed in the same manner as the first drainage sub-step S11. Also, similar to the first drainage sub-step S11 and the first water supply sub-step S12, if the water exchange apparatus 100 is equipped with a ball tap and a riser pipe, the control panel 4 may simultaneously perform the second drainage sub-step S21 and the second water supply sub-step S22.

In the second water supply sub-step S22, the control panel 4 supplies high-salinity water from the first water supply inlet 14 or low-salinity water from the second water supply inlet 15 to the breeding aquarium 8 as the second salinity water. At this time, if the first salinity water supplied in the first water supply sub-step S12 is high-salinity water from the first water supply inlet 14, the user controls the water supply switching unit 3 to switch to low-salinity water supply from the second water supply inlet 15. On the other hand, if the first salinity water supplied in the first water supply sub-step S12 is low-salinity water from the second water supply inlet 15, the user controls the water supply switching unit 3 to switch to high-salinity water supply from the first water supply inlet 14. The control of the water supply amount in the second water supply sub-step S22 is performed in the same manner as the control of the water supply amount in the first water supply sub-step S12. If the breeding system 1 is configured without the water supply switching unit 3, the user may control the water supply valves corresponding to the first water supply port 14 and the second water supply port 15, respectively, instead of the water supply switching unit 3.

The control panel 4 performs the second equalization sub-step S23 after the second drainage sub-step S21 and the second water supply sub-step S22. The second equalization sub-step S23 is performed in the same manner as the first equalization sub-step S13.

After the second homogenization sub-step S23, the control panel 4 determines whether the set water change period has elapsed (S24). In other words, after the second homogenization sub-step S23, the control panel 4 determines whether the predicted salinity concentration of the rearing water 26 when the next second drainage sub-step S21, second water supply sub-step S22, and second homogenization sub-step S23 are executed will be outside the predetermined range.

If S24 is No, the control panel 4 returns to the second drainage sub-step S21 and repeats the second drainage sub-step S21, the second water supply sub-step S22, and the second equalization sub-step S23. On the other hand, if S24 is Yes, the user ends the second step S20 and determines whether or not to continue raising saltwater fish (S25). In other words, if S24 is Yes, the next second drainage sub-step S21, the second water supply sub-step S22, and the second equalization sub-step S23 are not executed.

In S25, the determination can be made in the same manner as S15. If the answer is Yes in S25, the user returns to the first step S10. In this case as well, if the user determines that the water quality of the rearing water 26 at this point is maintained in such a good condition that water change is not necessary, the user may set a certain period of time during which water change is not performed before returning to the first step S10. On the other hand, if the answer is No in S25, the user ends the water change method.

It is preferable that the control panel 4 stops the circulation pump 6 and the heating and cooling unit 5 while the first drainage sub-step S11, the first water supply sub-step S12, the second drainage sub-step S21, or the second water supply sub-step S22 are being performed. Since the water level in the breeding aquarium 8 drops while these steps are being performed, water is no longer supplied to the biological filtration tank 9. If the circulation pump 6 continues to operate in this state, the breeding water 27 in the biological filtration tank 9 will become empty, causing problems such as air being mixed into the piping of the breeding system 1 or the circulation pump 6 running idly. This can cause gas disease in the saltwater fish being raised in the breeding aquarium 8.

In the above description, the user controls the water supply switching unit 3, the water supply valve 13, and the drain valve 12 by operating the control panel 4, but the present invention is not limited to this. For example, at least one of the water supply switching unit 3, the water supply valve 13, and the drain valve 12 may be manually controlled by the user.

In addition, since saltwater fish can be produced using the above water exchange method, the above water exchange method can be rephrased as a "saltwater fish production method" according to one embodiment of the present invention. In addition, the water exchange device according to one embodiment of the present invention is preferably a water exchange device used in the above water exchange method.

[Salinity prediction]
The water exchange method according to one embodiment of the present invention is preferably performed based on the predicted result of the salinity concentration of the breeding water 26. That is, it is preferable that the user predicts the salinity concentration of the breeding water 26 and sets the water exchange period (S1) before the first step S10 or the second step S20. Hereinafter, a method for predicting the salinity concentration of the breeding water 26 and a method for setting the water exchange period will be described with reference to Figures 3 to 5. According to this prediction method, it is possible to obtain a predicted salinity to be referenced after the first homogenization sub-step S13 or the second homogenization sub-step S23, and a predicted result of the period until the predicted salinity falls outside the predetermined range.

To predict the salinity, the user measures the salinity of the first salinity water supplied to the breeding tank 8 in the first water supply sub-step S12. The user also measures the salinity of the second salinity water supplied to the breeding tank 8 in the second water supply sub-step S22. The user also measures the salinity of the breeding water 26 before water replacement. By accurately grasping the salinity of the breeding water 26 and the water supplied in each step, the user can predict the salinity accurately. Note that the user only needs to measure the salinity of the first salinity water and the second salinity water once when the breeding system 1 is introduced. On the other hand, it is preferable for the user to measure the salinity of the breeding water 26 every time the first step S10 or the second step S20 is started, and correct the predicted result of the salinity each time, from the viewpoint of maintaining high prediction accuracy.

The salinity of the breeding water 26 can be predicted using the following formula (1):

C _a =C _b +a*(C _in -C _b )...(1)
Here, _Ca is the salinity (%) of the rearing water 26 after the water exchange, _Cb is the salinity (%) of the rearing water 26 before the water exchange, and _Cin is the water supplied during the water exchange (i.e., the first The salinity (%) of the water having the first salinity or the water having the second salinity is shown, and a indicates the water exchange rate for one water exchange.

In addition, when determining the water change rate a for one water change, the user determines how many times and how frequently the first step S10 or the second step S20 will be performed, i.e., the daily water change rate and the number of daily water changes.

The daily water exchange rate may be determined based on the rate at which the breeding water 26 becomes polluted, taking into account factors such as the density of the fish being reared in the breeding tank 8. The number of daily water changes may be determined to a number that reduces stress on the fish, while still preventing the breeding tank 8 from becoming polluted beyond an acceptable level.

For example, if the contamination of the breeding tank 8 can be sufficiently reduced by fewer water changes, the number of times that water changes cause stress to the breeding fish can also be reduced. However, if the number of water changes per day is too infrequent, the water change rate per water change will be large, and each water change will cause a lot of stress to the breeding fish.

The number of water changes per day may be, for example, once a day, or less than once. In this case, the number of times that water changes cause stress to the fish can be reduced. Water may also be changed two or more times a day. In this case, the stress on the fish can be reduced with a single water change.

Once the daily water exchange rate and the number of daily water exchanges are determined, the lower _limit of the water level of the breeding aquarium 8 can be determined by the following formula (2).

(L _u -L _l )=a'*(V/(A*n))...(2)
Here, L _u is the upper limit of the water level of the breeding tank 8 (m), L _l is the lower limit of the water level of the breeding tank 8 (m), a' is the daily water exchange rate of the breeding tank 8, and V is the volume of the breeding tank 8 ( ^m ), A is the area (m ² ) of the breeding tank 8, and n is the number of times water is changed per day.

By determining the upper and lower limits of the water level of the breeding aquarium 8 in this manner, the user can continuously perform the first step S10 and the second step S20 while keeping the water level of the breeding aquarium 8 within an appropriate range.

The user also sets a waiting period during which the user waits until the salinity of the breeding water 26 becomes uniform in the first homogenization sub-step S13 and the second homogenization sub-step S23. The waiting period may be set appropriately depending on the configuration of the breeding system 1, such as the size of the breeding aquarium 8 and the circulation speed of the circulation pump 6, so that the salinity of the breeding water 26 becomes uniform.

The upper and lower limits of the water level of the breeding water 26, the frequency of water changes, and the standby period do not need to be changed unless the configuration of the breeding system 1 or the type of fish being raised is changed. Therefore, the user does not need to set these parameters every time a water change is performed. Note that these parameters may be re-set as appropriate while observing the condition of the breeding water 26.

The user determines the water change period based on the predicted salinity concentration using the above formula (1) and the predetermined range CR of salinity concentration set according to the type of fish being raised, etc. In other words, the user can determine the period for repeatedly performing either the first step S10 or the second step S20 so that the salinity concentration of the breeding water 26 falls within the predetermined range CR.

Based on the above-mentioned method for predicting salinity, FIG. 3 shows an example of predicted salinity of the rearing water 26 when low-salinity water (tap water) is used in the water exchange method according to this embodiment, and FIG. 4 shows an example of predicted salinity of the rearing water 26 when high-salinity water (seawater) is used.

Fig. 3 shows the prediction results when, in the above formula (1), the salinity _Cb of the rearing water 26 before the water change is 2.7%, the salinity _Cin of the supplied water is 0%, and the water change period is 7 days. The upper graph of Fig. 3 shows the prediction results when the number of daily water changes n is 1, and the lower graph of Fig. 3 shows the prediction results when the number of daily water changes n is 2. Note that since the daily water change rate a' was always set to 0.1, the water change rate a when the number of daily water changes n is 1 was 0.1, and the water change rate a when the number of daily water changes n is 2 was 0.05.

Also, Fig. 4 shows the prediction results when the salinity _Cb of the rearing water 26 before the water change is 1.0%, the salinity _Cin of the supplied water is 3.4%, and the water change period is 7 days. The upper graph of Fig. 4 shows the prediction results when the number of daily water changes n is 1 time, and the lower graph of Fig. 4 shows the prediction results when the number of daily water changes n is 2 times. Note that the daily water change rate a' was set to 0.18 in both cases, so the water change rate a when the number of daily water changes n is 1 time is 0.18, and the water change rate a when the number of daily water changes n is 2 times is 0.09.

Figure 5 also shows an example of continuous water exchange using the water exchange method according to this embodiment, with periods of using low salinity water (tap water) and periods of using high salinity water (seawater) alternately repeated. That is, this shows an example of alternately repeating the first step S10 and the second step S20.

Here, the prediction results are for a case where the salinity _Cb of the rearing water 26 before water exchange is 2.0%, the salinity _Cin of the supplied water is 0% for low salinity water and 3.4% for high salinity water, and the water exchange period is 100 days. Note that the water supplied during the water exchange was switched between low salinity water and high salinity water every 14 days. The number of water exchanges per day n was 1 time, and the water exchange rate a was 0.02.

This method of predicting salinity makes it possible to predict the salinity of the rearing water 26 at any time during the water exchange method according to this embodiment. Therefore, the user can easily and accurately recognize the timing to end the first step S10 or the second step S20, or the timing to switch between the first step S10 and the second step S20.

Such a prediction of the salinity may be performed only once before the start of the first step S10 and the second step S20, or the prediction result may be corrected by measuring the salinity of the rearing water 26 and re-predicting the salinity at any time after the start of the water exchange method.

For example, a salinity sensor may be used to measure the salinity concentration. In the above-mentioned salinity prediction method and water exchange method, the salinity measurement is not performed frequently, so the maintenance costs of the salinity sensor can be reduced.

[Effect of removing pollutants from breeding water]
6 is a graph showing the results of a simulation of the transition of the concentration of pollutants in the rearing water 26 when the water exchange method according to the present embodiment is used. For comparison, the results of a simulation when a water exchange method according to the prior art is used are also shown.

In the simulation, it is assumed that (i) the concentration of pollutants in the breeding water 26 increases at a constant rate, and (ii) the water supplied to the breeding water 26 during water exchange does not contain pollutants or has a negligible concentration of pollutants. In addition, the pollutants assumed to be persistent organic matter, nitrate nitrogen, phosphate phosphorus, and other substances that are difficult to quickly remove from the breeding water 26 other than by water exchange. The "persistent organic matter" in Figure 6 includes these pollutants.

The method for predicting pollutants used in the simulation was based on the following formulas (3) and (4). The simulation results are shown by the solid line in Figure 6.

P _b =P _c +S*dt...(3)
P _a = P _b - a * P _b * dt ... (4)
Here, _Pc is the pollutant concentration (mg/L) of the breeding water 26 before contamination, _Pb is the pollutant concentration (mg/L) of the breeding water 26 immediately before water exchange, and _Pa is the pollutant concentration (mg/L) of the breeding water 26 immediately after water exchange. is the pollutant concentration (mg/L), dt is the time step (water exchange interval) (day), S is the rate of increase in the pollutant concentration in the breeding water 26 due to excretion by marine fish (mg/L/day), a is The water exchange rate after one water exchange is shown. The rate of increase in the pollutant concentration S was 1 mg/L/day, the water exchange rate a was 0.1, and the time step dt was 1 day.

A simulation was performed using the conventional continuous water exchange method (flowing water exchange) based on the following formula (5). The simulation results are shown by the dashed line in Figure 6.

P _t =S/a'*(1-e ^-a'*t )...(5)
Here, _Pt is the pollutant concentration (mg/L) of the breeding water 26, S is the rate of increase in the pollutant concentration (mg/L/day) of the breeding water 26, a' is the daily water exchange rate, and t is the number of days in the simulation. The rate of increase in the pollutant concentration S was 1 mg/L/day, and the daily water exchange rate a' was 0.1.

As shown in FIG. 6, according to the water exchange method of this embodiment, the pollutant concentration in the rearing water 26 remains at a lower concentration than in the continuous water exchange method of the conventional technology. Therefore, according to the water exchange method of this embodiment, it is simple and yet can achieve the same or better pollutant removal effect as the conventional technology.

An embodiment of the present invention will be described below with reference to Figures 7 and 8. As an embodiment of the present invention, an experiment was conducted to raise caught saltwater fish using a rearing system according to an embodiment of the present invention while implementing a water exchange method according to an embodiment of the present invention. The conditions of the experiment are as follows.

Breeding system: The one shown in FIG. 1 was used, and the capacity of the breeding tank 8 was 5 tons. High-salinity water: seawater with a salinity of 3.3%, low-salinity water: tap water with a salinity of 0%. Predetermined range CR of the salinity of the breeding water 26: upper limit Cmax=2.7%, lower limit Cmin=1.4%.
Daily water exchange rate: 0.055 (set the upper and lower water levels of the rearing water 26 accordingly)
Water change frequency per day: once Water change period: set so that the salinity falls within a specified range Experiment (salinity prediction) period: 144 days (saltwater fish were kept for an indefinite period during the period)
- Marine fish species: red spotted grouper, devil stinger, conger eel, red sea bream, filefish The salinity of the breeding water 26 was predicted using the above formula (1). The predicted salinity is shown by a solid line in FIG. 7. The salinity of the breeding water 26 was also measured irregularly. The measured salinity is shown as an outline circle in FIG. 7. At the start of each water change period (first step or second step), the predicted value of the salinity was updated based on the actual measured value of the salinity. The point in time when the update was performed is shown as a downward arrowhead in FIG. 7.

In addition, a large amount of high-salinity water (seawater) was supplied only once during the 144-day experimental period. The point in time when a large amount of high-salinity water (seawater) was supplied is indicated by a downward arrow in Figure 7.

Figure 7 shows the experimental results, comparing the predicted salinity values with the measured salinity values. Figure 8 shows the evaluation results of the saltwater fish raised (produced) in this experiment. The saltwater fish were evaluated as follows: live fish quality was "excellent," fresh fish quality was "good," processed fresh fish quality was "passable," and discarded fish quality was "poor." In other words, the order was "excellent," "good," "passable," and "poor," with "excellent" being the highest quality and "poor" being the lowest quality.

As shown in FIG. 7, the predicted value of the salinity of the rearing water was very close to the actual measured value. In other words, it was demonstrated that the method for predicting salinity according to one embodiment of the present invention has good prediction accuracy. Furthermore, as shown in FIG. 8, almost none of the saltwater fish reared (produced) by the water exchange method according to one embodiment of the present invention were "unacceptable," regardless of the number of days in storage (number of days reared). Therefore, it was demonstrated that the water exchange method according to one embodiment of the present invention makes it possible to stably rear and produce high-quality saltwater fish.

[Additional Notes]
The present invention is not limited to the above-described embodiments or examples, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments or examples are also included in the technical scope of the present invention.

100 Water exchange device 1 Rearing system 3 Water supply switching unit 4 Control panel 7 Water level sensor (water level detection unit)
8. Breeding tank (aquarium)
9 Biological filtration tank 12 Drain valve 13 Water supply valve 14 First water supply port 15 Second water supply port 26, 27 Rearing water Cmax Upper limit value Cmin Lower limit value S10 First step S11 First drainage sub-step S12 First water supply sub-step S13 First equalization sub-step S20 Second step S21 Second drainage sub-step S22 Second water supply sub-step S23 Second equalization sub-step

Claims (6)

a first water supply port for supplying high-salinity water, the salinity of which is equal to or higher than an upper limit of a predetermined range, to an aquarium tank that contains breeding water having a salinity within a predetermined range for breeding saltwater fish;
A second water supply port that supplies low-salinity water having a salinity equal to or lower than a lower limit of the predetermined range to the water tank;
a water level detection unit that detects a water level in the water tank in order to calculate an amount of water supplied from the first water supply port, an amount of water supplied from the second water supply port, and an amount of water discharged from the water tank;
A drain valve for controlling drainage of the rearing water from the aquarium;
a control panel that controls water supply from the first water supply port, water supply from the second water supply port, and water drainage by the drainage valve in response to the water level of the rearing water detected by the water level detection unit ,
The control panel has a function of executing a first step of performing each of the following sub-steps, (1) a first drainage sub-step, (2) a first water supply sub-step, and (3) a first homogenization sub-step performed after the first drainage sub-step and the first water supply sub-step, at least once for a predetermined period of time;
(1) a first drainage sub-step: draining the rearing water from the aquarium by controlling the drainage valve;
(2) First water supply sub-step: supplying water with a first salinity, which is set by selecting a value equal to or greater than an upper limit value of the predetermined range or a value equal to or less than a lower limit value of the predetermined range, to the aquarium from the first water supply port or the second water supply port so that the salinity of the rearing water after the first homogenization sub-step falls within a predetermined range;
(3) a first homogenization sub-step: homogenizing the salinity concentration of the rearing water in the aquarium;
the predetermined period is a period from when the predicted salinity of the rearing water after the most recent first homogenization sub-step is within the predetermined range to when the predicted salinity of the rearing water when the first drainage sub-step, the first water supply sub-step, and the first homogenization sub-step are next executed falls outside the predetermined range;
In the first step,
When it is determined that the predetermined period has not elapsed, the first drainage sub-step, the first water supply sub-step, and the first equalization sub-step are further executed;
When it is determined that the predetermined period has elapsed, the subsequent first drainage sub-step, the first water supply sub-step, and the first equalization sub-step are not executed . The water exchange device according to claim 1, further comprising a water supply switching unit that switches between the water supply from the first water supply port and the water supply from the second water supply port. The water exchange device according to claim 1 or 2, wherein the drainage rate from the water tank is greater than at least one of the water supply rate from the first water supply port and the water supply rate from the second water supply port. A water exchange method executed by a control panel that controls water supply and drainage to an aquarium, comprising a first step of performing each of the following substeps, (1) a first drainage substep, (2) a first water supply substep, and (3) a first homogenization substep performed after the first drainage substep and the first water supply substep, at least once for a predetermined period of time ;
(1) A first drainage sub-step: draining water for breeding saltwater fish from the aquarium;
(2) a first water supply sub-step: supplying water having a first salinity to the aquarium, the first salinity being set by selecting a value equal to or greater than an upper limit value of the predetermined range or a value equal to or less than a lower limit value of the predetermined range, so that the salinity of the rearing water after the first homogenization sub-step falls within a predetermined range;
(3) a first homogenization sub-step: homogenizing the salinity concentration of the rearing water in the aquarium ;
the predetermined period is a period from when the predicted salinity of the rearing water after the most recent first homogenization sub-step is within the predetermined range to when the predicted salinity of the rearing water when the first drainage sub-step, the first water supply sub-step, and the first homogenization sub-step are next executed falls outside the predetermined range;
In the first step,
When it is determined that the predetermined period has not elapsed, the first drainage sub-step, the first water supply sub-step, and the first equalization sub-step are further executed;
A water exchange method, in which, if it is determined that the predetermined period has elapsed, the subsequent first drainage sub-step, the first water supply sub-step, and the first equalization sub-step are not executed. 5. The water exchange method according to claim 4, further comprising a second step of carrying out, after the first step, each of the following substeps, (4) a second drainage substep, (5) a second water supply substep, and (6) a second equalization substep carried out after the second drainage substep and the second water supply substep, at least once.
(4) Second drainage sub-step: draining the water for breeding saltwater fish from the aquarium;
(5) Second water supply sub-step: supplying water of a second salinity to the aquarium, the second salinity being set to be equal to or less than the lower limit if the first salinity is equal to or more than the upper limit if the first salinity is equal to or less than the lower limit, so that the salinity of the rearing water after the second homogenization sub-step falls within a predetermined range;
(6) Second homogenization sub-step: homogenizing the salinity concentration of the breeding water in the aquarium. A water exchange method executed by a control panel that controls water supply and drainage to an aquarium, comprising a first step of performing each of the following substeps, (1) a first drainage substep, (2) a first water supply substep, and (3) a first homogenization substep performed after the first drainage substep and the first water supply substep, at least once for a predetermined period of time ;
(1) A first drainage sub-step: draining water for breeding saltwater fish from the aquarium;
(2) a first water supply sub-step: supplying water having a first salinity to the aquarium, the first salinity being set by selecting a value equal to or greater than an upper limit value of the predetermined range or a value equal to or less than a lower limit value of the predetermined range, so that the salinity of the rearing water after the first homogenization sub-step falls within a predetermined range;
(3) a first homogenization sub-step: homogenizing the salinity concentration of the rearing water in the aquarium ;
the predetermined period is a period from when the predicted salinity of the rearing water after the most recent first homogenization sub-step is within the predetermined range to when the predicted salinity of the rearing water when the first drainage sub-step, the first water supply sub-step, and the first homogenization sub-step are next executed falls outside the predetermined range;
In the first step,
When it is determined that the predetermined period has not elapsed, the first drainage sub-step, the first water supply sub-step, and the first equalization sub-step are further executed;
A method for producing marine fish in an aquarium in which the salinity of the rearing water is adjusted by the water exchange method, in which, if it is determined that the specified period has elapsed, the subsequent first drainage sub-step, the first water supply sub-step, and the first homogenization sub-step are not performed.

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