Water tank for rearing larval fish and rearing device for larval fish

Abstract

This water tank for rearing larval fish comprises: a flat surface part extending in the lateral direction; a pair of curved surface parts that are respectively connected to one lateral end and the other lateral end of the flat surface part, and that bulge in mutually opposite sides in the lateral direction and extend upward; and a pair of side surface parts that are respectively connected to the pair of curved surface parts and extend upward. When the interval in the lateral direction between the upper ends of the pair of side surface parts is denoted as W (mm) and the height from the flat surface part to the upper ends of the side surface parts is denoted as H (mm), the relation 1.12≤W / H≤1.90 is satisfied.

Description

Aquarium for raising larvae and larvae rearing device

[0001] The present invention relates to an aquarium for raising larvae and a larvae raising device equipped with the aquarium.

[0002] Conventionally, aquariums for raising eel larvae have been proposed. For example, Patent Document 1 proposes a tank with a semi-cylindrical bottom (length 1800 mm × width 800 mm × height 800 mm).

[0003] International Publication WO2015 / 093616

[0004] The aquarium described in Patent Document 1 has a bottom formed of a continuous concave curve, with the lowest part of the bottom projecting downward. With this type of bottom shape, when feeding the larvae in the aquarium, the feed supplied to the aquarium is concentrated at the curved part (lower end) of the bottom of the aquarium. This narrows the feeding area, making it difficult to efficiently feed the many larvae in the aquarium. Therefore, the aquarium described in Patent Document 1 has room for improvement in terms of increasing the number of larvae reared, i.e., the number of larvae produced per unit volume of water (also known as production efficiency).

[0005] Furthermore, if larvae remain near the bottom of the tank after feeding, they may rub their heads against the tank bottom, resulting in dislocation of the jaw. To reduce this phenomenon, it is necessary to use a water current flowing at an appropriate speed to drive larvae away from the bottom after feeding. On the other hand, if the water current is too fast, the larvae are more likely to suffer from spinal deformities, such as broken spines. To facilitate water injection control, if the water injection rate (amount of water injected per given time) is constant, the shape of the tank must be appropriately designed to ensure that the water flows at an appropriate speed along the inner surface (including the bottom) of the tank in order to reduce the risk of larval abnormalities (dislocation, deformities, etc.). The shape of the tank described in Patent Document 1 is not designed with consideration given to reducing the occurrence of abnormal larval fish, and this also leaves room for improvement.

[0006] The present invention has been made to solve the above problems, and its purpose is to provide an aquarium for raising larvae, and a larvae raising device equipped with such a tank, which can increase the number of larvae raised (production efficiency) while reducing the occurrence of abnormalities in the larvae (dislocation, deformities, etc.) by appropriately setting the shape of the aquarium.

[0007] According to one aspect of the present invention, an aquarium for raising larvae has a flat portion extending laterally, a pair of curved portions connected to one end and the other end of the flat portion in the horizontal direction and bulging out to opposite sides in the horizontal direction and extending upward, and a pair of side portions connected to each of the pair of curved portions and extending upward, wherein when the distance in the horizontal direction between each upper end of the pair of side portions is W (mm) and the height from the flat portion to each upper end of the pair of side portions is H (mm), the following is satisfied: 1.12≦W / H≦1.90 ... (1)

[0008] Another aspect of the present invention provides a larval fish rearing device comprising the above-described aquarium, a water injection section for injecting water into the aquarium, and a drainage section for draining water that is poured into the aquarium and exceeds the specified capacity of the aquarium.

[0009] A further aspect of the present invention provides a larval fish rearing device comprising the above-described aquarium, a water injection section for injecting water into the aquarium, and a drainage section for draining water that has been injected into the aquarium and exceeds the aquarium's specified capacity, wherein the water injection section has a water injection pipe extending in the longitudinal direction of the aquarium, the water injection pipe having a plurality of water injection ports formed in a row in the longitudinal direction, and the drainage sections are arranged in a row in the longitudinal direction, with the number of ports being less than the number of the water injection ports.

[0010] It is possible to increase the number of larvae reared (production efficiency) while reducing the occurrence of abnormalities (dislocation, deformities, etc.) in the larvae.

[0011] 1 is a perspective view showing the general configuration of a larvae rearing device according to one embodiment of the present invention; FIG. 2 is a plan view showing the general configuration of a water inlet and outlet section of an aquarium provided in the rearing device; FIG. 3 is a front view showing the configuration of the area around the outlet section of the aquarium; FIG. 4 is a cross-sectional view of the aquarium when cut along a plane perpendicular to the longitudinal direction; FIG. 5 is a cross-sectional view showing another configuration of the aquarium; FIG. 6 is a cross-sectional view showing yet another configuration of the aquarium; FIG. 7 is a cross-sectional view showing the configuration of an aquarium for a comparative example; FIG. 8 is a graph showing the growth rate of larvae by age in days when the larvae are reared in half-pipe aquariums of different lengths; FIG. 9 is a graph showing the growth rate of larvae by age in days when the larvae are reared in Kreisel aquariums of different diameters; FIG. 10 is an explanatory diagram showing the distribution of water flow in a cross section perpendicular to the longitudinal direction in each aquarium of the example and the comparative example; FIG. 11 is an explanatory diagram showing the distribution of water flow in the longitudinal direction in each aquarium of the example;

[0012] The following describes an embodiment of the present invention with reference to the drawings.

[0013] 1. Regarding the Rearing Apparatus (1-1. Overview of the Rearing Apparatus) Fig. 1 is a perspective view showing the general configuration of a rearing apparatus 100 for larvae of this embodiment. The rearing apparatus 100 comprises an aquarium 10, a water inlet section 20, and a drainage section 30. In this embodiment, eel larvae are considered as an example of the larvae to be reared. Note that the rearing apparatus 100 of this embodiment can also be applied to rearing larvae other than eels.

[0014] The aquarium 10 has a generally U-shaped cross section and is elongated in one direction. For ease of explanation, directions are defined as follows in this specification. First, the direction in which the aquarium 10 extends (longitudinal direction, depth direction) is defined as direction A. Two directions perpendicular to direction A in a cross section perpendicular to direction A are defined as direction B and direction C, respectively. Direction B is the height direction of the aquarium 10, i.e., the up-down direction. Direction C is the lateral direction (width direction) of the aquarium 10.

[0015] The aquarium 10 has a wall 10W that is open at the top and concave at the bottom. The wall 10W extends in the direction A and connects the front wall 10F and the rear wall 10B. The front wall 10F and the rear wall 10B are located on opposite sides of each other in the direction A. The wall 10W is supported by a plurality of ribs 40, allowing the aquarium 10 to be installed in a predetermined position. Further details of the aquarium 10 will be described later.

[0016] Rearing water is supplied into the aquarium 10 by a water injection unit 20. The rearing water is, for example, seawater. Hereinafter, the rearing water will be simply referred to as "water." Larvae are raised in the aquarium 10 by putting them into the water in the aquarium 10 and feeding them periodically. When feeding, water injection by the water injection unit 20 is stopped, and water injection is resumed after feeding. A predetermined amount of water is stored in the aquarium 10 by injecting water by the water injection unit 20. Water exceeding the above-mentioned amount due to water injection (overflow water) is drained from the drainage unit 30.

[0017] Thus, rearing device 100 comprises aquarium 10 for rearing larvae, a water injection unit 20 that injects water into aquarium 10, and a drainage unit 30 that drains water that has been poured into aquarium 10 and exceeds the predetermined capacity of aquarium 10. With this configuration, water injection by water injection unit 20 and drainage by drainage unit 30 can be performed simultaneously, thereby creating an appropriate water flow within aquarium 10. Therefore, in terms of creating a flow field within aquarium 10 that is favorable for larvae, it can be said that it is desirable for rearing device 100 to have the above configuration.

[0018] Feeding is performed, for example, as follows: A feeding tube is inserted from the top of the aquarium 10 toward the bottom, and food is placed (applied) on the bottom through the feeding tube. When a lighting device placed above the aquarium 10 is turned on, the larvae move (swim) in the opposite direction to the lighting device due to their natural behavior (negative phototaxis). In other words, the larvae move from the top to the bottom within the aquarium 10. When the larvae reach the food placed on the bottom of the aquarium 10, they ingest the food. This type of feeding is performed, for example, five times a day, every two hours, but the frequency of feeding can be adjusted as appropriate depending on the type of larvae, the breeding season, etc.

[0019] If food remains on the bottom of the aquarium 10, the bottom of the aquarium 10 and the water in the aquarium 10 will become dirty, making it easier for bacteria to grow within the aquarium 10. Because larvae are susceptible to bacteria, the aquarium 10 needs to be cleaned periodically. For this reason, two aquariums 10 are installed side by side, and tank changes are performed periodically (e.g., every other day) by transferring larvae from one aquarium 10 to the other aquarium 10. This tank change allows larvae to continue being raised in one aquarium 10 while the other aquarium 10 is being cleaned. Tank changes can be performed, for example, by connecting the connection ports 10P on the front walls 10F of the two aquariums 10 with a hose and using the siphon principle to transfer water from one aquarium 10 to the other aquarium 10 via the hose.

[0020] (1-2. Details of the water injection section and drainage section) Figure 2 is a plan view showing the general configuration of the water injection section 20 and drainage section 30 of the aquarium 10. The water injection section 20 injects water into the aquarium 10. The water injection section 20 has a water injection pipe 21 and a connecting pipe 22. The water injection pipe 21 is a pipe that extends in direction A, that is, in the longitudinal direction of the aquarium 10.

[0021] The water injection pipe 21 has a plurality of water injection ports 21a. The water injection ports 21a are formed side by side in the direction A at the lower end of the outer circumferential surface of the water injection pipe 21. In this embodiment, nine water injection ports 21a are provided on each side in the direction A from the center of the water injection pipe 21. In other words, the total number of water injection ports 21a is 18. Note that the number of water injection ports 21a is not limited to 18, and other numbers may be used.

[0022] The connection pipe 22 is connected to the vicinity of the center of the water injection pipe 21 in the direction A. The end of the connection pipe 22 opposite to the water injection pipe 21 is connected to a water supply pump via a connection hose.

[0023] Water supplied from the water supply pump and flowing through the connecting pipe 22 branches off at the connection with the water inlet pipe 21 to flow in opposite directions in the direction A. Water is then supplied (injected) into the water tank 10 from each of the water inlet ports 21a aligned in the direction A.

[0024] Two drainage sections 30 are provided side by side with a gap between them in direction A. The two drainage sections 30 are located on opposite sides of the center of water injection pipe 21 in direction A and are located equidistant from the center of water injection pipe 21. In other words, the two drainage sections 30 are located symmetrically with respect to the center of water injection pipe 21 in direction A. The number of drainage sections 30 is not limited to two as described above, and may be one, or three or more.

[0025] FIG. 3 is a front view showing the configuration of the drainage unit 30 and its vicinity of the aquarium 10. The drainage unit 30 has a drainage tube 31 and a main body 32. The drainage tube 31 is a cylindrical body extending in the direction B. An inlet 31a through which water from the aquarium 10 flows is located at the lower end of the drainage tube 31. When the water level is at S0 when a predetermined amount of water is stored in the aquarium 10, the drainage tube 31 is fixed to the aquarium 10 via the main body 32 so that the inlet 31a is located below position S0. Note that the water filling pipe 21 of the water filling unit 20 described above is also located below position S0.

[0026] A strainer 31b is attached to the drain tube portion 31. The strainer 31b is a mesh member that is provided to surround the inlet 31a. The strainer 31b prevents the larvae in the aquarium 10 from entering the inlet 31a.

[0027] The main body 32 extends in the direction C and communicates with the drain tube 31. The main body 32 is provided by penetrating the wall 10W of the aquarium 10. The main body 32 is fixed to the wall 10W of the aquarium 10 so that its lowest point is located at the same position as or lower than position S0.

[0028] Water in the aquarium 10 passes through the mesh (gaps) of the strainer 31b, enters the inlet 31a, and then enters the inside of the drain tube 31. When the water inlet 20 injects more water into the aquarium 10 than the predetermined capacity, the water level inside the drain tube 31 attempts to rise above position S0. Because the drain tube 31 is connected to the main body 32, the water above position S0 flows into the main body 32 and is discharged outside the aquarium 10.

[0029] In this embodiment, the number of drainage units 30 is two, which is fewer than the number of water inlets 21a of the water injection unit 20 (e.g., 18). In this case, the flow of water injected from the water inlet 21a, flowing through the aquarium 10 and toward the drainage unit 30 can be spread in direction A. Therefore, from the perspective of creating a flow field in the aquarium 10 that is favorable for the larvae, it is desirable to arrange a number of drainage units 30 fewer than the number of water inlets 21a side by side in direction A.

[0030] Furthermore, in order to reliably create a flow field in the aquarium 10 that is favorable for the larval fish, it is desirable to make the distribution of the flow paths through which water flows in the aquarium 10 as symmetrical as possible in the direction A. In this regard, as shown in Figure 2, it is desirable that the water inlet 21a and the drainage section 30 be arranged symmetrically in the direction A with respect to the center of the direction A.

[0031] 2. Details of the Water Tank Figure 4 is a cross-sectional view of the water tank 10 described above. Note that Figure 4 shows a cross-section of the water tank 10 cut along a plane perpendicular to direction A. For convenience, Figure 4 omits the illustration of the water inlet section 20 and the water outlet section 30 described above. This method of illustration (how the cross-sections are shown) will also be used in the following Figures 5 to 7.

[0032] Aquarium 10 has a flat surface portion 11, a curved surface portion 12, and a side surface portion 13. Flat surface portion 11, curved surface portion 12, and side surface portion 13 are formed on an inner surface 10S of wall portion 10W of aquarium 10. In this embodiment, aquarium 10 is elongated in direction A as described above, and therefore flat surface portion 11, curved surface portion 12, and side surface portion 13 are also elongated in direction A.

[0033] The flat surface portion 11 is located at the bottom of the inner surface 10S of the aquarium 10, extending in the C direction. A pair of curved surface portions 12 are provided on both sides of the flat surface portion 11 in the C direction. More specifically, the curved surface portions 12 are connected to one end 11a and the other end 11b of the flat surface portion 11 in the C direction, and bulge out in opposite directions in the C direction, extending upward.

[0034] In the following description, when distinguishing between the pair of curved surface portions 12, the curved surface portion 12 connected to one end 11a of the flat surface portion 11 in the C direction will be referred to as the first curved surface portion 12a. The curved surface portion 12 connected to the other end 11b of the flat surface portion 11 in the C direction will be referred to as the second curved surface portion 12b. The first curved surface portion 12a and the second curved surface portion 12b are each curved in a shape that protrudes from the inside to the outside of the aquarium 10 in the cross section of Figure 4. Therefore, the distance between the first curved surface portion 12a and the second curved surface portion 12b in the C direction increases from the side connected to the flat surface portion 11 toward the opposite side (upward).

[0035] The curved surface portion 12 (first curved surface portion 12a, second curved surface portion 12b) is formed in an arc shape with a constant radius of curvature R (distance from the center of curvature O) in the cross section of Fig. 4. Note that the curved surface portion 12 may be formed in a curved shape other than an arc shape (for example, a shape in which the radius of curvature R changes midway).

[0036] The side surface portions 13 are connected to each of the pair of curved surface portions 12 and extend upward. Therefore, a pair of side surface portions 13 is provided corresponding to each of the pair of curved surface portions 12. Here, of the pair of side surface portions 13, the side surface portion 13 connected to the first curved surface portion 12a is also referred to as the first side surface portion 13a, and the side surface portion 13 connected to the second curved surface portion 12b is also referred to as the second side surface portion 13b. In this case, it can be said that the first side surface portion 13a is connected to the first curved surface portion 12a and extends upward. Similarly, it can be said that the second side surface portion 13b is connected to the second curved surface portion 12b and extends upward. In this embodiment, the first side surface portion 13a and the second side surface portion 13b are positioned parallel to each other. In other words, the distance between the first side surface portion 13a and the second side surface portion 13b in the C direction is constant.

[0037] As shown in Figure 4, the distance in the C direction between the top ends of the pair of side portions 13, i.e., the first side portion 13a and the second side portion 13b, is defined as W (mm). The height from the flat portion 11 to the top end of each of the pair of side portions 13 is defined as H (mm). In this case, the water tank 10 of this embodiment satisfies the following conditional expression (1). Note that the above W can be rephrased as the width of the water tank 10. Also, the above H can be rephrased as the height of the water tank 10. 1.12 ≤ W / H ≤ 1.90 (1)

[0038] 4, if the width of flat surface portion 11 in the direction C is P (mm), where P = 100 mm, the radius of curvature of first curved surface portion 12a and second curved surface portion 12b is R, where R = 230 mm, and water tank 10 is designed with W = 460 mm and H = 370 mm, then W / H = 1.24. Therefore, with the above design, it is possible to realize water tank 10 that satisfies conditional expression (1).

[0039] Figure 5 is a cross-sectional view showing another configuration of aquarium 10. Aquarium 10 in Figure 5 has a configuration in which P and W of aquarium 10 in Figure 4 are changed to P = 200 mm and W = 560 mm (R and H are the same as in Figure 4, and the center of curvature of R is O or O'). In aquarium 10 in Figure 5, W / H = 1.51. Therefore, aquarium 10 that satisfies conditional formula (1) can be realized with the design in Figure 5 as well.

[0040] Figure 6 is a cross-sectional view showing yet another configuration of aquarium 10. Aquarium 10 in Figure 6 has a configuration in which P and W of aquarium 10 in Figure 4 are changed to P = 300 mm and W = 660 mm (R and H are the same as in Figure 4). In aquarium 10 in Figure 6, W / H = 1.78. Therefore, aquarium 10 that satisfies conditional expression (1) can be realized with the design in Figure 6 as well.

[0041] In the configuration of the aquarium 10 shown in Figures 4 to 6, i.e., in which a pair of curved portions 12 (first curved portion 12a, second curved portion 12b) are connected to both ends of the flat portion 11 in the C direction, and each side portion 13 (first side portion 13a, second side portion 13b) is further connected to each curved portion 12 and extends upward, the flat portion 11 is located on the bottom of the aquarium 10. In this case, when feeding the larvae in the aquarium 10, food can be placed on the flat portion 11, allowing the feeding area to be expanded in the C direction. Therefore, unlike conventional aquariums without a flat portion 11 (aquariums with a simple concave cross section), food is not concentrated in a narrow area at the bottom. As a result, by simply expanding the aquarium 10 slightly in the C direction (without expanding the aquarium 10 more than necessary), many larvae can be efficiently fed, thereby increasing the number of larvae reared (production efficiency).

[0042] Furthermore, by ensuring that the W / H value is within a range satisfying conditional expression (1), a water flow with an appropriate flow rate can be generated within the aquarium 10. For example, after feeding, water can be poured downward from near one of the side surfaces 13 (e.g., the first side surface 13a) at a predetermined flow rate, generating a water flow along one of the curved surfaces 12 (e.g., the first curved surface 12a) and the flat surface 11, and a water flow at an appropriate flow rate toward the other curved surface 12 (e.g., the second curved surface 12b) and the other side surface 13 (e.g., the second side surface 13b). This allows larvae that remain near the flat surface 11 after feeding to be driven toward the other side surface 13 (e.g., the second side surface 13b), allowing them to swim appropriately within the aquarium 10. This reduces the risk of larvae rubbing their heads against the bottom of the aquarium 10 (e.g., the flat surface 11) after feeding, resulting in jaw dislocation.

[0043] Furthermore, if the flow velocity is too fast, abnormalities (deformities) such as broken spines in the larvae are likely to occur. By ensuring that the value of W / H is within a range that satisfies conditional expression (1), it is possible to generate an appropriate flow velocity in the aquarium 10 when water is poured in, thereby reducing the occurrence of such abnormalities.

[0044] In other words, by providing a flat surface 11 on the bottom surface of the aquarium 10 and appropriately setting the cross-sectional shape of the aquarium 10 (the range of values ​​of W / H) using conditional formula (1), it is possible to increase the number of larvae that can be raised while reducing the occurrence of abnormalities (dislocation, deformities, etc.) in the larvae.

[0045] In order to reliably realize a flow rate that can reduce jaw dislocation and deformities in larvae when water is poured into the aquarium 10 after feeding, it is desirable for the aquarium 10 of this embodiment to further satisfy the following conditional formula (1a). The aquarium 10 shown in Figures 4 to 6 further satisfies conditional formula (1a) and is a desirable form: 1.24≦W / H≦1.78 ... (1a)

[0046] Furthermore, from the perspective of reliably realizing an aquarium 10 that satisfies conditional formula (1a), it is desirable that the aquarium 10 of this embodiment satisfy the following conditional formula (2a). The aquarium 10 shown in FIGS. 4 to 6 further satisfies conditional formula (2a), and is a desirable form: 100 mm≦P≦300 mm (2a)

[0047] In the aforementioned Patent Document 1, since the width and height of the aquarium are 800 mm and 800 mm, respectively, W / H = 800 / 800 = 1 can be considered. Furthermore, since there is no flat surface on the bottom of the aquarium, P can also be considered to be 0 mm. With this configuration, as mentioned above, the feed supplied to the aquarium is concentrated at the lower end of the bottom of the aquarium, resulting in a narrow feeding area, making it difficult to increase the number of larvae reared. From the perspective of increasing the number of larvae reared, assuming that the longitudinal length of the aquarium is constant, it is preferable to set P > 0 mm and provide a flat surface (even if only slightly wide) on the bottom of the aquarium. In this regard, the lower limit of W / H, i.e., 1.12, the median between the conventional W / H value of 1 and the lower limit of 1.24 in conditional formula (1a), can be considered as the critical point at which at least the effects of this embodiment are achieved.

[0048] FIG. 7 is a cross-sectional view showing the configuration of aquarium 10A. The aquarium 10A in FIG. 7 has a configuration in which P and W of the aquarium 10 in FIG. 4 are changed to P = 400 mm and W = 760 mm (R and H are the same as in FIG. 4). The aquarium 10 in FIG. 7 has a W / H ratio of 2.05. This design has a large value of P, which indicates the width of the flat surface 11 of the aquarium 10, making it more effective than the configurations in FIGS. 4 to 6 in terms of expanding the feeding area. However, the configuration in FIG. 7 has such a large width of the flat surface 11 that, at a constant water injection rate, it is difficult to achieve a water flow velocity (e.g., 0.045 m / s) sufficient to dispel larvae that remain near the flat surface 11 after feeding, as shown in the simulation results described below. From this, the upper limit of W / H can be considered to be the median value between the upper limit of "1.78" of conditional expression (1a) and the value of W / H in the configuration of FIG. 7, "2.05," i.e., "1.90," as the critical point at which at least the effect of this embodiment can be obtained.

[0049] The above-mentioned conditional expression (1) defines the range (upper and lower limits) of W / H based on this idea.

[0050] Similarly, from the viewpoint of expanding the feeding area within the aquarium 10 as much as possible, the lower limit of P can be considered to be the median value between the conventional value of P, "0 mm," and the lower limit of conditional formula (2a), "100 mm," i.e., "50 mm," as the critical point at which at least the effect of this embodiment can be obtained.

[0051] Furthermore, from the viewpoint of realizing a water flow velocity capable of driving away larvae that remain near the flat portion 11 after feeding, the upper limit of P can be considered to be the median value between the upper limit of "300 mm" in conditional formula (2a) and the value of P in the configuration of FIG. 7, "400 mm," i.e., "350 mm," as the critical point at which at least the effect of this embodiment can be obtained.

[0052] From the above, in order to reliably realize a water tank 10 that satisfies conditional expression (1), it is desirable that the water tank 10 of this embodiment satisfy the following conditional expression (2): 50 mm≦P≦350 mm (2)

[0053] Furthermore, the aquarium 10 of this embodiment is elongated in the direction A, as shown in FIG. 1 . In other words, the aquarium 10 is elongated in the direction A, which is perpendicular to a cross section defined by the normal direction (direction B) and the lateral direction (direction C) of the planar portion 11. In this case, the number of larvae (absolute number) that can be reared can be easily increased depending on the length of the aquarium 10 in the direction A. For example, by multiplying the length of the aquarium 10 in the direction A by n (n is a positive number greater than 1), the number of larvae that can be reared can also be simply multiplied by n. In other words, from the perspective of increasing the number of larvae that can be reared, it is desirable for the aquarium 10 to be elongated in the direction A, as in this embodiment.

[0054] Furthermore, the following considerations revealed that extending the aquarium 10 to any desired length in the A direction does not adversely affect the growth of larvae. Figure 8 is a graph schematically illustrating the growth rate (distribution of total length) of larvae by day in half-pipe aquaria (with three capacity types: 20 L, 30 L, and 100 L). The half-pipe aquaria are formed by placing a cylinder horizontally, cutting it horizontally along a plane containing the central axis, and extending both ends upward. The 20 L half-pipe aquaria has an opening width of 247 mm and a length in the A direction of 497 mm. The 30 L half-pipe aquaria has an opening width of 228 mm and a length in the A direction of 752 mm. The 100 L half-pipe aquaria has an opening width of 230 mm and a length in the A direction of 2491 mm. That is, the opening widths of the half-pipe aquaria are approximately constant, but the lengths in the A direction are different.

[0055] It should be noted that the aquarium 10 of this embodiment has the flat surface 11 as described above, but in the considerations shown in Figure 8, since we only wanted to examine the effect of the length of the aquarium in direction A on the growth rate of the larvae, that is, to eliminate the effect of the flat surface 11, we considered an aquarium without a flat surface on the bottom as the above-mentioned half-pipe aquarium.

[0056] From the figure, it can be seen that the maximum total length of the larvae increases from 20 days to 40 days of age regardless of whether the half-pipe tank is 20 L, 30 L, or 100 L. Therefore, it can be said that it is possible to increase the size of the tank 10 in direction A without adversely affecting the growth of the larvae.

[0057] The curved surface portions 12 (first curved surface portion 12a, second curved surface portion 12b) of the aquarium 10 are formed in an arc shape in the cross section shown in Figure 4, etc. As mentioned above, the curved surface portions 12 may have any shape that protrudes from the inside to the outside of the aquarium 10, and are not limited to the arc shape. However, if the curved surface portions 12 are arc-shaped, the direction of the water flow can be smoothly changed throughout the curved surface portions 12 when water is poured along the inner surface 10S of the aquarium 10. This reduces loss due to a decrease in the water flow velocity. Therefore, an arc-shaped curved surface portion 12 is desirable in that it makes it easier to achieve a desired flow velocity at each position on the inner surface 10S of the aquarium 10.

[0058] 4 to 6 exceeds 500 mm, the swimming ability of the larvae is such that it is difficult for them to reach the flat portion 11 (the food placed on the flat portion 11) from near the water surface in the larvae tank 10, making it difficult to properly raise the larvae. For example, the amount of food intake by the larvae decreases, which can lead to a delay in the growth of the larvae and, ultimately, a decrease in the survival rate of the larvae.

[0059] 9 is a graph showing the growth rate of larvae by day (distribution of total length of larvae) in Kreisel tanks (with three types of capacity: 20 L, 60 L, and 100 L). The Kreisel tank is a tank in which a cylinder is placed horizontally and cut along a plane parallel to the central axis, and the width of the opening at the cut surface is shorter than the inner diameter of the cylinder, and the tank has a wall extending around half the circumference or more.

[0060] In each Kreisel tank, the inner diameter and height of the 20 L tank are both 410 mm, the inner diameter and height of the 60 L tank are both 533 mm, and the inner diameter and height of the 100 L tank are both 671 mm.

[0061] The aquarium 10 of this embodiment has the flat surface 11 as described above, but in the verification shown in Figure 9, we wanted to examine only the effect of the inner diameter (= height) of the aquarium as the effect on the growth rate of the larvae, that is, to eliminate the effect of the flat surface 11, so we considered an aquarium without a flat surface on the bottom as the above-mentioned Kreisel aquarium.

[0062] 9 shows that in the 60 L and 100 L aquariums with heights exceeding 500 mm, the range of total length of the larvae is narrower and the growth rate of the larvae is lower at both 20 and 40 days of age compared to the 20 L aquarium with a height of 500 mm or less. Therefore, from the perspective of making it easier for the larvae to reach the food on the bottom during feeding and enabling proper rearing of the larvae, it can be said that the height H of the aquarium is preferably 500 mm or less. In other words, it is desirable for the aquarium 10 of this embodiment to satisfy the following conditional formula (3): H≦500 mm (3)

[0063] In particular, from the viewpoint of ensuring that the larvae can easily reach the food on the bottom during feeding and ensure that the larvae are properly reared, it can be seen from Figure 8 that the height H of the aquarium is preferably 410 mm or less. In other words, it is desirable that the aquarium 10 of this embodiment further satisfies the following conditional expression (3a): H≦410 mm (3a)

[0064] 3. Examples Next, examples of the aquarium 10 according to the present embodiment will be described together with comparative examples. Below, the water flow distribution within each of the three aquariums 10 shown in Figures 4 to 6 and the aquarium 10A shown in Figure 7 (particularly the distribution within a cross section perpendicular to direction A) was specifically verified by simulation.

[0065] First, as shown in Figure 4, the width of the flat surface 11 in the direction C was P (mm), and the aquarium 10 in Example 1 was designed with P = 100 mm, W = 460 mm, and H = 370 mm. The radius of curvature of the curved surface 12 of the aquarium 10 was R, and R = 230 mm. The length of the aquarium 10 in the direction A was 1500 mm. The height H (= 370 mm) of the aquarium was set to a height (500 mm or less) sufficient for the larvae to swim downward and ingest food during feeding.

[0066] As shown in FIG. 5, P and W of water tank 10 of Example 1 were changed to P = 200 mm and W = 560 mm, and the other parameters (H, R, and L) were kept the same as in Example 1, and water tank 10 of Example 2 was designed.

[0067] As shown in FIG. 6, P and W of water tank 10 of Example 1 were changed to P = 300 mm and W = 660 mm, and the other parameters (H, R, and L) were kept the same as in Example 1, and water tank 10 of Example 3 was designed.

[0068] As shown in FIG. 7, P and W of water tank 10 of Example 1 were changed to P = 400 mm and W = 760 mm, and the other parameters (H, R, and L) were kept the same as in Example 1, and water tank 10A of Comparative Example 1 was designed.

[0069] As shown in FIG. 2 , the water injection pipe 21 of the water injection section 20 used to inject water into each of the water tanks (water tanks 10 and 10A) in Examples 1 to 3 and Comparative Example 1 was assumed to have nine water injection ports 21a formed at 70 mm intervals on one side and the other side of the water injection port 21a from the center in the direction A (a total of 18 water injection ports 21a). The diameter of the water injection ports 21a was 3.5 mm. Furthermore, the distance D shown in FIG. 3 when a predetermined amount of water was filled in the water tank by pouring water from each water injection port 21a of the water injection pipe 21 was set to D = 78 mm. Note that distance D refers to the distance in the direction B from the top of the side surface 13 of the water tank to the initial water level S0 in the water tank (the water level when a predetermined amount of water was filled in the water tank 10). When the distance from the bottom surface (flat surface portion 11) of water tank 10 to position S0 is the height H0 of drainage portion 30 (see FIG. 10), H0=H-D0=370-78=292 mm.

[0070] In addition, it was assumed that water was injected into the water tank by positioning water injection pipe 21 near one side of the water tank at a position lower than position S0, supplying water to connecting pipe 22 at a rate of 10 L / min, and discharging seawater downward from each water inlet 21a. Here, one side surface portion, one curved surface portion, flat surface portion, other curved surface portion, and other side surface portion refer to first side surface portion 13a, first curved surface portion 12a, flat surface portion 11, second curved surface portion 12b, and second side surface portion 13b shown in Figures 4 to 7. It was assumed that drainage portions 30 were positioned near water injection pipe 21 and symmetrically with respect to the center of water injection pipe 21 in direction A.

[0071] In each of Examples 1 to 3 and Comparative Example 1, the distribution of water flow (flow velocity, flow rate) was analyzed using multiphase flow analysis using the VOF (Volume of Fluid) method. The VOF method is a type of free surface flow analysis technique used in gas-liquid multiphase flow analysis. Figure 10 schematically shows the water flow distribution in each of the water tanks in Examples 1 to 3 and Comparative Example 1 for 40 seconds from the start of water pouring. Note that Figure 10 shows the water flow distribution in a cross section perpendicular to the longitudinal direction in each water tank. In Figure 10, dashed lines indicate the water flow, and solid lines indicate the overall water flow.

[0072] As a result of the analysis, the following was found: First, in Examples 1 to 3, water flows along the inner surface of the tank (one side surface, one curved surface, flat surface, other curved surface, other side surface), and a good water flow field is formed within the tank.

[0073] It has been found that when the bottom flow velocity (the flow velocity of the water flow near the flat surface) is below 0.045 m / s, it becomes difficult to drive the larvae away from the bottom with the water current, and the larvae tend to rub their heads against the bottom, increasing the incidence of jaw dislocation. In this regard, in Examples 1 to 3, analysis results show that a bottom flow velocity of 0.045 m / s to 0.05 m / s is ensured, which is thought to reduce the occurrence of jaw dislocation in the larvae. Furthermore, after feeding, the larvae swim in the tank on a gentle water current flowing at 0.05 m / s or less, which is thought to reduce the likelihood of larvae suffering from deformities such as broken spines.

[0074] The above-mentioned bottom flow velocity condition for reducing jaw dislocation of larvae must be considered for the entire flat surface, that is, from one end of the flat surface (the end connected to one curved surface) to the other end (the end connected to the other curved surface). However, if a flow velocity of 0.045 m / s or more is satisfied at the downstream end of the flat surface, where the flow velocity is relatively slower than at the upstream end of the flat surface, the flow velocity of 0.045 m / s or more will be satisfied throughout the entire flat surface. Therefore, in the example of Figure 10, it is sufficient to satisfy a bottom flow velocity of 0.045 m / s or more at least at the other end (downstream end) of the flat surface.

[0075] In contrast, in Comparative Example 1, the bottom flow velocity (particularly the flow velocity at the downstream end of the flat portion) was 0.04 m / s, which was below the standard of 0.045 m / s. This is thought to be because the bottom of the aquarium in Comparative Example 1 was too wide, so that water flowing along one side portion passed near the bottom and did not reach the other side portion, i.e., the water flowed away from the bottom and the other side portion. In Comparative Example 1, the bottom flow velocity was slow, so the larvae remained near the bottom even after feeding, raising concerns that the larvae would be more likely to lose their jaws.

[0076] Furthermore, as mentioned above, if the water flow is too fast, the larvae are more likely to suffer deformities such as broken spines. In order to create an appropriate water flow in the aquarium, the upper limit of the flow velocity of the water flowing along the curved surface portion upstream of the flat surface portion is preferably 0.1 m / s or less, and more preferably 0.08 m / s or less.

[0077] The water tanks of Examples 1 to 3 satisfy the respective conditional expressions of this embodiment described above, and are fully expected to provide the effects of this embodiment described above.

[0078] 11 and 12 show schematic diagrams of the water flow distribution in the longitudinal direction (direction A) in each of the water tanks in Examples 1 to 3 and Comparative Example 1. It was found that the water flow distribution in the longitudinal direction was nearly symmetrical with respect to the center of direction A in all of the water tanks.

[0079] [4. Other] In the above example, the height H0 of the drainage section 30 was set to 292 mm for an aquarium 10 with a height of 370 mm. However, the height H0 of the drainage section 30 may be any height equal to or less than the height H of the aquarium 10. In this embodiment, as indicated by the above-mentioned conditional expressions (3) and (3a), H≦500 mm, preferably H≦410 mm, and therefore, it can be concluded that the height H0 of the drainage section 30 is also H≦500 mm, preferably H≦410 mm. In this case, the lateral width W of the aquarium 10 according to the present invention can also be rephrased as the lateral width W of the water surface when a predetermined amount of water is stored in the aquarium 10. The height H of the aquarium 10 can also be rephrased as the height H from the flat surface 11 to the water surface.

[0080] Furthermore, the height H of the aquarium 10 is a parameter that determines the volume of the aquarium 10 (the maximum amount of water that can be accommodated). On the other hand, if the drainage section 30 is installed at a height equal to or lower than the height H of the aquarium 10, the height H0 of the drainage section 30 also becomes a parameter that determines the maximum amount of water that can be accommodated in the aquarium 10. In this way, the height H of the aquarium 10 and the height H0 of the drainage section 30 are both parameters that determine the maximum amount of water that can be accommodated in the aquarium 10. Therefore, the above-mentioned conditional expressions (1) and (1a) can be replaced by the following conditional expressions (A) and (B), respectively. That is, where H0 (mm) is the height of the drainage section 30 from the flat surface 11 of the aquarium 10, the following conditions are satisfied: 1.12≦W / H0≦1.90 (A) 1.24≦W / H0≦1.78 (B)

[0081] The water tank 10 of this embodiment satisfies the above-mentioned conditional expression (2), i.e., 50 mm≦P≦350 mm. Here, in the water tank 10 of Example 1, if the width P of the flat surface 11 is changed from 100 mm to 50 mm, the width W of the water tank 10 decreases by 50 mm from 460 mm to 410 mm. Similarly, in the water tank 10 of Example 3, if the width P of the flat surface 11 is changed from 300 mm to 350 mm, the width W of the water tank 10 increases by 50 mm from 660 mm to 710 mm. Therefore, the possible range of W of the water tank 10 is 410 mm≦W≦710 mm. Therefore, in terms of the W / P ratio, the water tank 10 of this embodiment can also be said to satisfy the following conditional expression (4): 2.03≦W / P≦8.20 (4)

[0082] In particular, it can be said that a desirable range for W / P is a range that satisfies the following conditional expression (4a) based on the values ​​shown in Examples 1 to 3: 2.20≦W / P≦4.60 (4a)

[0083] In the aquarium 10 shown in Figure 4 and elsewhere, the first and second side surfaces 13a and 13b are preferably parallel to each other as in this embodiment, but they do not have to be parallel. For example, the distance between the first and second side surfaces 13a and 13b in the direction C may increase slightly upward. In this case, the distance W in the direction C is the maximum distance between the first and second side surfaces 13a and 13b (the distance between their upper ends).

[0084] [5. Supplementary Notes] The aquarium and breeding device described in this embodiment can be expressed as follows.

[0085] The aquarium of appendix (1) is an aquarium for raising larvae, and has a flat portion extending laterally, a pair of curved surface portions connected to one end and the other end of the flat portion in the horizontal direction and bulging out to opposite sides in the horizontal direction and extending upward, and a pair of side surfaces connected to each of the pair of curved surface portions and extending upward, and satisfies 1.12≦W / H≦1.90 ... (1) where W (mm) is the horizontal distance between each upper end of the pair of side surfaces and H (mm) is the height from the flat portion to each upper end of the pair of side surfaces.

[0086] The water tank of supplementary note (2) is the water tank according to supplementary note (1), which further satisfies the following condition: 1.24≦W / H≦1.78 (1a).

[0087] The water tank of Supplementary Note (3) is the water tank of Supplementary Note (1), in which, when the width of the flat portion in the lateral direction is P (mm), the following condition is satisfied: 50 mm≦P≦350 mm (2).

[0088] The water tank of Supplementary Note (4) is the water tank described in Supplementary Note (2), in which, when the width of the flat portion in the lateral direction is P (mm), the following condition is satisfied: 100 mm≦P≦300 mm (2a).

[0089] The water tank of supplementary note (5) is the water tank according to any one of supplementary notes (1) to (4), and satisfies the following condition: H≦500 mm (3).

[0090] The water tank of supplementary note (6) is the water tank described in supplementary note (5), which further satisfies the following condition: H≦410 mm (3a).

[0091] The water tank of Supplementary Note (7) is the water tank described in any one of Supplementary Notes (1) to (6), which is elongated in a direction perpendicular to a cross section defined by including the normal direction of the planar portion and the lateral direction.

[0092] The water tank of supplementary note (8) is the water tank according to any one of supplementary notes (1) to (7), wherein the curved surface portion is arc-shaped.

[0093] The larval fish rearing device of Appendix (9) comprises an aquarium described in any one of Appendixes (1) to (8), a water injection unit that injects water into the aquarium, and a drainage unit that drains water that is poured into the aquarium and exceeds the predetermined capacity of the aquarium.

[0094] The larval fish rearing device of appendix (10) is the larval fish rearing device described in appendix (9), and when the height of the drainage section from the flat section is H0 (mm), the following is satisfied instead of formula (1): 1.12≦W / H0≦1.90 ... (A).

[0095] The larval fish rearing device of Appendix (10) can also be rephrased as follows: That is, the larval fish rearing device described in Appendix (10) comprises an aquarium, a water inlet section for injecting water into the aquarium, and a drain section for draining water that has been poured into the aquarium and exceeds a predetermined capacity of the aquarium, wherein the aquarium has a flat section extending in the horizontal direction, a pair of curved section sections connected to one end and the other end of the flat section in the horizontal direction and bulging out to opposite sides in the horizontal direction and extending upward, and a pair of side sections connected to each of the pair of curved section sections and extending upward, wherein when the horizontal distance between the upper ends of the pair of side sections is W (mm) and the height of the drain section from the flat section is H0 (mm), the following is satisfied: 1.12≦W / H0≦1.90 ... (A).

[0096] The larval fish rearing device of appendix (10) preferably satisfies the following condition: 1.24≦W / H0≦1.78 (B).

[0097] The larval fish rearing device of Appendix (11) comprises the aquarium described in Appendix (7), a water injection section for injecting water into the aquarium, and a drainage section for draining water that has been injected into the aquarium and exceeds the predetermined capacity of the aquarium, wherein the water injection section has a water injection pipe extending in the longitudinal direction of the aquarium, the water injection pipe has a plurality of water injection ports formed in a row in the longitudinal direction, and the number of drainage sections is less than the number of the water injection ports and is arranged in a row in the longitudinal direction.

[0098] The rearing device for larvae according to supplementary note (12) is the rearing device according to supplementary note (11), wherein the water inlet and the drainage section are arranged symmetrically in the longitudinal direction with respect to the center of the longitudinal direction.

[0099] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and the invention can be expanded or modified without departing from the spirit of the invention.

[0100] The aquarium for raising larvae of the present invention can be used to raise, for example, eel larvae.

[0101] DESCRIPTION OF SYMBOLS 10 Aquarium 11 Flat portion 11a One end portion 11b Other end portion 12 Curved portion 12a First curved portion (one of a pair of curved portions) 12b Second curved portion (the other of the pair of curved portions) 13 Side portion 13a First side portion (one of a pair of side portions) 13b Second side portion (the other of the pair of side portions) 20 Water injection portion 21 Water injection pipe 21a Water injection port 30 Drainage portion 100 Rearing device A Longitudinal direction B Lateral direction H Height of side portion H0 Height of drainage portion P Width W Spacing

Claims

1. An aquarium for raising larvae, comprising: a flat portion extending laterally; a pair of curved surface portions connected to one end and the other end of the flat portion in the horizontal direction, bulging out in opposite directions in the horizontal direction and extending upward; and a pair of side surfaces connected to each of the pair of curved surface portions and extending upward, wherein the distance in the horizontal direction between the upper ends of the pair of side surfaces is W (mm), and the height from the flat portion to the upper ends of the pair of side surfaces is H (mm), the aquarium satisfies 1.12≦W / H≦1.90 ... (1).

2. The water tank according to claim 1, further satisfying the following condition: 1.24≦W / H≦1.78 (1a).

3. The water tank according to claim 1, wherein the following condition is satisfied: 50 mm≦P≦350 mm (2), where P (mm) is the width in the lateral direction of the flat surface portion.

4. The water tank according to claim 2, wherein the following condition is satisfied: 100 mm≦P≦300 mm (2a), where P (mm) is the width in the lateral direction of the flat surface portion.

5. The water tank according to claim 1, which satisfies the following condition: H≦500 mm (3).

6. The water tank according to claim 5, further satisfying the following condition: H≦410 mm (3a).

7. The water tank according to claim 1, which is elongated in a direction perpendicular to a cross section defined by the normal direction of the planar portion and the lateral direction.

8. The aquarium according to claim 1, wherein the curved surface is arc-shaped.

9. A fish larvae rearing device comprising: an aquarium according to any one of claims 1 to 8; a water inlet section for injecting water into the aquarium; and a drainage section for draining water that is poured into the aquarium and exceeds the predetermined capacity of the aquarium.

10. A larval fish rearing device as described in claim 9, wherein, when the height of the drainage section from the flat section is H0 (mm), the following is satisfied instead of formula (1): 1.12≦W / H0≦1.90 ... (A).

11. A breeding device for larvae, comprising: an aquarium according to claim 7; a water injection section for injecting water into the aquarium; and a drainage section for draining water that has been injected into the aquarium and exceeds the aquarium's specified capacity, wherein the water injection section has a water injection pipe extending in the longitudinal direction of the aquarium, the water injection pipe having a plurality of water injection ports formed in a row in the longitudinal direction, and the number of drainage sections is less than the number of the water injection ports and is arranged in a row in the longitudinal direction.

12. A larval fish rearing device as described in claim 11, wherein the water inlet and the water outlet are arranged symmetrically in the longitudinal direction with respect to the center of the longitudinal direction.

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