Cephalopod breeding method, protozoa prevention method, protozoa extermination method and cephalopod larva

Abstract

A cephalopod breeding method, which is for breeding cephalopod larvae in a breeding water tank, comprises, during the floating breeding period of the cephalopod larvae, forming a high concentration area where the salinity concentration is higher compared to seawater at the bottom of the breeding water tank and, after the passage of a predetermined time from the formation of the high concentration area, removing the high concentration area.

Description

Cephalopod breeding method, protozoan prevention method, protozoan extermination method, and cephalopod larvae

[0001] The present disclosure relates to a method for rearing cephalopods, a method for preventing protozoa, a method for eliminating protozoa, and cephalopod larvae.

[0002] In recent years, consumer interest in palatability and resource conservation has increased, and there is a demand for the development of cephalopod farming techniques.

[0003] For example, Patent Document 1 discloses an octopus rearing shelter and an octopus farming system.

[0004] JP 2017-006054 A

[0005] In order to increase cephalopod production, it is necessary to reduce the mortality rate of larvae, but conventional aquaculture techniques often result in high mortality rates.

[0006] The present disclosure aims to provide a technique for reducing the mortality rate when rearing cephalopod larvae.

[0007] The present disclosure provides the following: [1] A method for rearing cephalopod larvae in a breeding tank, the method comprising: forming a high-concentration region having a higher salt concentration than seawater at the bottom of the breeding tank during the floating breeding period of the cephalopod larvae; and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region. [2] The cephalopod rearing method described in [1], wherein the forming of the high-concentration region and the removal of the high-concentration region are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age. [3] The cephalopod rearing method described in [1] or [2], wherein the bottom of the breeding tank is within 5 cm of the deepest part of the breeding tank. [4] The cephalopod rearing method described in any one of [1] to [3], wherein the salinity in the high-concentration region is 40‰ or higher. [5] The cephalopod rearing method according to any one of [1] to [4], wherein forming the high-concentration region comprises supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank. [6] The cephalopod rearing method according to [5], wherein the highly concentrated salt water and / or the solid salt comprises at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. [7] The cephalopod rearing method according to [5] or [6], wherein, in forming the high-concentration region, the highly concentrated salt water and / or solid salt is supplied to the bottom of the breeding tank so as not to mix with the water above. [8] The cephalopod rearing method according to [7], wherein, in forming the high-concentration region, the highly concentrated salt water is supplied using a supply means connecting the outside of the breeding tank to the bottom of the breeding tank. [9] The cephalopod rearing method according to [8], wherein the supply means is a pipe.

[10] The cephalopod rearing method according to [8] or [9], wherein, in removing the high-concentration region, the supply means is used as a removal means for removing water present in the high-concentration region.

[11] The cephalopod rearing method according to any one of [1] to

[10] , wherein, in removing the high-concentration region, the water present in the high-concentration region is removed using a removal means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[12] The cephalopod rearing method according to any one of [1] to

[11] , wherein, in removing the high-concentration region, the water present in the high-concentration region is removed using a removal means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[13] The cephalopod rearing method according to

[12] , wherein the removal means is a pipe.

[14] The cephalopod rearing method according to any one of [1] to

[13] , wherein the formation of the high-concentration region and the removal of the high-concentration region are carried out multiple times during the rearing period.

[15] The cephalopod rearing method according to any one of [1] to

[14] , wherein the protozoan density in the water of the rearing tank is controlled to be 350 individuals / ml or less during the floating rearing period of the cephalopod larvae.

[16] The cephalopod rearing method according to

[15] , wherein the protozoan that is the subject of the protozoan density measurement is a flagellate or a ciliate.

[17] A cephalopod rearing method for rearing cephalopod larvae in a rearing tank, wherein the protozoan density in the water of the rearing tank is controlled to be 350 individuals / ml or less during the floating rearing period of the cephalopod larvae.

[18] The cephalopod rearing method according to

[17] , wherein the protozoa to be measured for protozoan density are flagellates or ciliates.

[19] A method for preventing the occurrence of protozoa in a rearing tank when rearing cephalopod larvae in the rearing tank, the method comprising: forming a high-concentration region having a higher salt concentration than seawater at the bottom of the rearing tank during the floating rearing period of the cephalopod larvae; and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region.

[20] The protozoan prevention method according to

[19] , wherein the formation of the high-concentration region and the removal of the high-concentration region are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age.

[21] The protozoan prevention method according to

[19] or

[20] , wherein the bottom of the rearing tank is within 5 cm of the deepest part of the rearing tank.

[22] The protozoan prevention method according to any one of

[19] to

[21] , wherein the salt concentration in the high-concentration region is 40‰ or higher.

[23] The protozoan prevention method according to any one of

[19] to

[22] , wherein forming the high-concentration region comprises supplying highly concentrated salt water and / or solid salt to the bottom of the breeding aquarium.

[24] The protozoan prevention method according to

[23] , wherein the highly concentrated salt water and / or the solid salt comprises at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

[25] The protozoan prevention method according to

[23] or

[24] , wherein, in forming the high-concentration region, the highly concentrated salt water and / or solid salt is supplied to the bottom of the breeding aquarium so as not to mix with the water above.

[26] The protozoan prevention method according to

[25] , wherein, in forming the high-concentration region, the highly concentrated salt water is supplied using a supply means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[27] The protozoan prevention method according to

[26] , wherein the supply means is piping.

[28] The protozoan prevention method according to

[26] or

[27] , wherein, in removing the high-concentration region, the supply means is used as a removal means for removing water present in the high-concentration region.

[29] The protozoan prevention method according to any one of

[19] to

[28] , wherein the predetermined time is 15 minutes or more and 60 minutes or less.

[30] The protozoan prevention method according to any one of

[19] to

[29] , wherein removing the high-concentration region involves removing water present in the high-concentration region using a removal means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[31] The protozoan prevention method according to

[30] , wherein the removal means is piping.

[32] The protozoan prevention method according to any one of

[19] to

[31] , wherein forming the high-concentration region and removing the high-concentration region are carried out multiple times during the breeding period.

[33] The protozoan prevention method according to any one of

[19] to

[32] , wherein the protozoan is a flagellate or a ciliate.

[34] The protozoan prevention method according to any one of

[19] to

[33] , wherein during the floating breeding period, the protozoan density in the water of the breeding aquarium is controlled to be 350 individuals / ml or less.

[35] A method for eliminating protozoa from a breeding tank when raising cephalopod larvae in the breeding tank, the method comprising: forming a high-concentration region having a higher salt concentration than seawater at the bottom of the breeding tank during the floating breeding period of the cephalopod larvae; and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region.

[36] The protozoan extermination method described in

[35] , wherein the forming of the high-concentration region and the removal of the high-concentration region are carried out during at least a portion of the period until the cephalopod larvae reach 15 days of age.

[37] The protozoan extermination method of

[35] or

[36] , wherein the bottom of the breeding aquarium is within 5 cm of the deepest part of the breeding aquarium.

[38] The protozoan extermination method of any one of

[35] to

[37] , wherein the salinity in the high-concentration region is 40‰ or higher.

[39] The protozoan extermination method of any one of

[35] to

[38] , wherein forming the high-concentration region comprises supplying highly concentrated salt water and / or solid salt to the bottom of the breeding aquarium.

[40] The protozoan extermination method of

[39] , wherein the highly concentrated salt water and / or the solid salt comprises at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

[41] The protozoan extermination method of

[39] or

[40] , wherein forming the high-concentration region comprises supplying the highly concentrated salt water and / or solid salt to the bottom of the breeding aquarium so as not to mix with the water above.

[42] The protozoan extermination method of

[41] , wherein, in forming the high-concentration region, the highly concentrated salt water is supplied using a supply means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[43] The protozoan extermination method of

[42] , wherein the supply means is piping.

[44] The protozoan extermination method of

[42] or

[43] , wherein, in removing the high-concentration region, the supply means is used as a removal means for removing water present in the high-concentration region.

[45] The protozoan extermination method of any one of

[35] to

[44] , wherein the predetermined time is 15 minutes or more and 60 minutes or less.

[46] The protozoan extermination method of any one of

[35] to

[45] , wherein, in removing the high-concentration region, the water present in the high-concentration region is removed using a removal means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[47] The protozoan extermination method of

[46] , wherein the removal means is piping.

[48] ​​The protozoan control method according to any one of

[35] to

[47] , wherein the formation of the high-concentration region and the removal of the high-concentration region are carried out multiple times during the rearing period.

[49] The protozoan control method according to any one of

[35] to

[48] , wherein the protozoan is a flagellate or a ciliate.

[50] The protozoan control method according to any one of

[35] to

[49] , wherein the protozoan density in the water of the breeding tank is controlled to 350 protozoan individuals / ml or less during the floating breeding period.

[51] Cephalopod larvae raised in a breeding tank by a breeding method including: forming a high-concentration region having a higher salt concentration than seawater at the bottom of the breeding tank during the floating breeding period of the cephalopod larvae; and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region.

[52] The cephalopod larvae according to

[51] , wherein the formation of the high-concentration region and the removal of the high-concentration region are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age.

[53] The cephalopod larvae according to

[51] or

[52] , wherein the bottom of the breeding tank is within 5 cm of the deepest part of the breeding tank.

[54] The cephalopod larvae according to any one of

[51] to

[53] , wherein the salinity in the high-concentration region is 40‰ or higher.

[55] The cephalopod larvae according to any one of

[51] to

[54] , wherein forming the high-concentration region comprises supplying highly saline water and / or solid salts to the bottom of the breeding tank.

[56] The cephalopod larvae according to

[55] , wherein the highly saline water and / or solid salts comprise at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

[57] The cephalopod larvae according to

[55] or

[56] , wherein, in forming the high-concentration region, the highly saline water and / or solid salts are supplied to the bottom of the breeding tank so as not to mix with the water above.

[58] The cephalopod larvae according to

[57] , wherein, in forming the high-concentration region, the highly concentrated salt water is supplied using a supply means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[59] The cephalopod larvae according to

[58] , wherein the supply means is a pipe.

[60] The cephalopod larvae according to

[58] or

[59] , wherein, in removing the high-concentration region, the supply means is used as a removal means for removing water present in the high-concentration region.

[61] The cephalopod larvae according to any one of

[51] to

[60] , wherein the predetermined time is 15 minutes or more and 60 minutes or less.

[62] The cephalopod larvae according to any one of

[51] to

[61] , wherein in removing the high-concentration region, water present in the high-concentration region is removed using a removal means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium.

[63] The cephalopod larvae according to

[62] , wherein the removal means is piping.

[64] The cephalopod larvae according to any one of

[51] to

[63] , wherein the formation of the high-concentration region and the removal of the high-concentration region are carried out multiple times during the breeding period.

[65] Protozoa-resistant cephalopod larvae.

[66] The cephalopod larvae according to

[65] , wherein the protozoa are flagellates or ciliates.

[67] Cephalopod larvae according to

[65] or

[66] , which are reared in a rearing tank by a rearing method comprising: forming a high-concentration region having a higher salt concentration than seawater at the bottom of the rearing tank during a floating rearing period of the cephalopod larvae; and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region, and which have a daily mortality rate of 8.00 or less even when the protozoan density in the water of the rearing tank is 150 individuals / ml or more during the floating rearing period of the cephalopod larvae.

[68] Cephalopod larvae according to

[67] , in which the high-concentration region is formed once or multiple times.

[0008] The present disclosure aims to provide a technique for reducing the mortality rate when rearing cephalopod larvae.

[0009] 1(a) and 1(b) are schematic diagrams of an apparatus for carrying out the cephalopod rearing method according to the present embodiment. FIG. 2 is a diagram illustrating the procedure for forming a high-concentration region in a rearing tank.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0011] [Cephalopod Rearing Apparatus and Cephalopod Rearing Method] Fig. 1 is a schematic diagram of a cephalopod rearing apparatus for carrying out the cephalopod rearing method described in this embodiment. As shown in Fig. 1, the cephalopod rearing apparatus 1 includes a rearing tank 2 for rearing cephalopods, a water exchange unit 3 for exchanging water in the rearing tank 2, and a salt supply unit 4 for forming a high-salinity region in the rearing tank 2. Fig. 1(a) shows a vertical cross section of the rearing tank 2, and Fig. 1(b) shows a top view of the rearing tank 2 near its bottom. Cephalopods are reared in the rearing tank 2 using saltwater for rearing. In this specification, saltwater may be simply referred to as water.

[0012] There are no particular limitations on the cephalopods that can be reared using the cephalopod rearing device 1, but the target species are those whose larvae float in the ocean after hatching during the growth stage. Examples of such cephalopods include, but are not limited to, bigfin reef squid, Japanese common squid, spear squid, Octopus maya, Japanese octopus, common octopus, Pacific octopus, willow octopus, and long-legged octopus.

[0013] As described above, cephalopods float in the water of the breeding tank 2 during the larval stage after hatching. The cephalopod breeding device 1 described above can be used during the floating breeding period of cephalopod larvae. In this disclosure, the floating breeding period refers to the period after hatching during which cephalopods are raised in a floating state before settling to the bottom. For example, in the case of common octopus, the floating breeding period is approximately 0 to 23 days old. In this disclosure, age refers to the number of days elapsed since hatching, with the hatching date being considered as day 0. Furthermore, in the case of common octopus, the body length of common octopus during the floating breeding period is approximately 0.8 mm or less. However, the age and body length of common octopus during the floating breeding period may vary depending on the breeding environment and are not limited to the above ranges. Furthermore, since the age and body length during the settlement transition period vary depending on the species, the period during which the cephalopod breeding device 1 can be used may be individually set depending on the species.

[0014] As shown in Fig. 1, the cephalopod rearing apparatus 1 includes a water exchange unit 3 that exchanges water in the rearing tank 2. The water exchange unit 3 includes a water inlet unit 31 and a drainage unit 32. The water exchange unit 3 may also include an aeration system 33, as shown in Fig. 1. In addition to the system shown in Fig. 1, the cephalopod rearing apparatus 1 may also be provided with other equipment related to rearing cephalopods, such as a food supply system.

[0015] The shape and capacity of the breeding tank 2 are not particularly limited. FIG. 1 shows an example in which the shape of the space inside the breeding tank 2 that stores water W, which is saltwater for breeding, is cylindrical with a circular bottom. When water is stored in a cylindrical space that is circular in plan view as shown in FIG. 1, it is possible to suppress uneven water movement within the breeding tank 2 to some extent. It is preferable to ensure a capacity sufficient for breeding cephalopod larvae during their floating breeding period. The capacity of the breeding tank 2 is, for example, 100 L to 150 x 10 ３ L, and 500L to 150 x 10 ３ The cephalopod larvae may be introduced into the breeding tank 2 so that the number of cephalopod larvae per 1 L of water is 1 to 10.

[0016] The water injection unit 31 supplies saltwater for breeding into the breeding tank 2. The saltwater for breeding is, for example, seawater that has been subjected to a predetermined process, such as sterilization. The water injection unit 31 is a pipe that supplies water to be injected into the breeding tank 2 from an external supply source. The external supply source may be, for example, a tank or a tank that stores saltwater that has been subjected to a predetermined process. A water injection port is provided at the end of the water injection unit 31. The water injection port may be located, for example, at an upper position within the breeding tank 2 and may be configured to supply saltwater horizontally along the circumferential direction near the periphery, i.e., near the sidewall of the breeding tank 2, as shown in FIG. 1( b). Although not shown, water injection by the water injection unit 31 may be performed, for example, by driving a pump provided in the pipe that constitutes the water injection unit 31.

[0017] The drainage unit 32 drains saltwater from the breeding aquarium 2. The drainage unit 32 is a pipe provided with a drainage outlet 32a that takes in water from the breeding aquarium 2, and the water taken in from the drainage outlet 32a is discharged into the breeding aquarium 2 via the pipe.

[0018] As shown in FIGS. 1( a) and 1(b), the pipes constituting the drainage unit 32, including the drain outlet 32a, may extend vertically at the center C of the breeding aquarium 2. In this case, water is discharged from the center of the breeding aquarium 2. The water inside the breeding aquarium 2 may be discharged, for example, to the ocean. Before being discharged into the ocean, the water may be sterilized or disinfected. The sterilization or disinfection may be performed using, for example, chemicals, chlorine, ozone, electricity, or a filter, as long as live bacteria or protozoa are not discharged. These methods may be combined. The drainage unit 32 may be operated by a pump (not shown) attached to the pipes constituting the drainage unit 32. Alternatively, a pipe extending radially from the center C of the breeding aquarium 2 may be connected to the vertically extending pipes.

[0019] The aeration device 33 is installed, for example, near the bottom of the breeding aquarium 2 at the center C, and supplies air bubbles taken into the breeding aquarium 2 by an air pump or the like into the water W. Although not shown, the aeration device 33 may include a gas supply unit installed near the bottom of the breeding aquarium 2 to release bubbles into the water, and a gas pipe connected to the air pump to supply the air taken in by the air pump to the gas supply unit. As shown in FIG. 1 , when the aeration operation is performed with the gas supply unit located at the bottom of the breeding aquarium 2 at the center C, a flow of bubbles rising in the water may be formed around the drain outlet 32a located near the center C of the breeding aquarium 2.

[0020] As a method for supplying air into the water W of the breeding aquarium 2 without using the aeration equipment 33, for example, the water injection unit 31 may be provided above the water. By placing the water injection unit 31 at a position away from the water surface and allowing saltwater for breeding to fall from the water injection unit 31, air can be mixed into the water as the saltwater falls. In this way, the method for supplying air into the water W of the breeding aquarium 2 is not limited to the method using the aeration equipment 33.

[0021] In the cephalopod rearing device 1, water can be exchanged in the breeding tank 2 by simultaneously injecting water using the water injector 31 and draining water using the drainage unit 32. By setting the same amount of water injected per unit time by the water injector 31 and the same amount of water drained per unit time by the drainage unit 32, water exchange is performed while maintaining the water volume in the breeding tank 2. The amounts of water injected and drained do not need to be the same, as long as a sufficient amount of water is secured in the breeding tank 2 to support cephalopod larval rearing. Water injection, drainage, or both may be temporarily stopped, as long as a sufficient amount of water is secured in the breeding tank 2 to support cephalopod rearing. Furthermore, as shown in FIG. 1( b ), if the water injector 31 is located near the periphery of the breeding tank 2 and the drain outlet 32a of the drainage unit 32 is located near the center C of the breeding tank 2, a water flow from the periphery toward the center C is generated in the breeding tank 2. Furthermore, when the water is poured into and discharged from the water injection section 31 and the water discharge section 32 while the aeration equipment 33 is operating, part of the water flow goes upward, so that a gentle circulating flow is formed both vertically and horizontally.

[0022] The locations of the water injection unit 31, the drainage unit 32, and the aeration equipment 33 are merely examples and can be changed as appropriate. For example, in the example shown in Fig. 1, instead of injecting water by the water injection unit 31 near the water surface in the breeding aquarium 2, water may be injected near the bottom of the water. Furthermore, drainage by the drainage unit 32 may also be performed from near the bottom of the water at the center C of the breeding aquarium 2. In this case, injection and drainage may be performed below the floating area A where cephalopod larvae can float.

[0023] Furthermore, the cephalopod breeding device 1 is provided with a salt supplying section 4 at the bottom of the breeding tank 2 to form a high-concentration area with a salt concentration higher than that of seawater.

[0024] The bottom of the breeding tank 2, where the high-concentration region is formed, refers to the portion of the area containing saltwater in the breeding tank 2 that is close to the bottom. The bottom of the breeding tank 2 is characterized by the accumulation of organic matter such as dead cephalopod larvae, leftover food, and excrement from the cephalopods being raised, and is also a source of the emergence of the protozoa that are the subject of this disclosure.

[0025] Specifically, the bottom of the breeding tank 2 refers to a height range of 15 cm or less, 10 cm or less, 5 cm or less, 3 cm or less, 1 cm or less, or 0.5 cm or less from the bottom of the water W in the breeding tank 2. The bottom may also be a height range of 20% or less, 15% or less, 10% or less, 5% or less, 3% or less, or 1% or less of the depth of the water W in the breeding tank 2. These ranges are areas where dead cephalopod larvae, residual food, excrement, and other organic matter generated when breeding cephalopod larvae in the breeding tank 2, may accumulate as sediments. Many breeding tanks 2 used for breeding cephalopod larvae have a depth of approximately 80 cm to 200 cm. When the water depth is 80 cm, the above-mentioned height ranges are 18.75% or less, 12.5% ​​or less, 6.25% or less, 3.75% or less, 1.25% or less, or 0.625% or less from the bottom of the water W, respectively, which are sufficiently small ranges relative to the water depth. The lower limit of the bottom of the breeding aquarium 2, where the high-concentration region is formed, is not a problem as long as it is set to include sediments. For example, the bottom range may be 0.01 cm or more, 0.03 cm or more, 0.05 cm or more, 0.07 cm or more, or 0.1 cm or more from the bottom of the water W. The lower limit of the bottom may also be set to 0.005% or more, 0.01% or more, 0.03% or more, 0.5% or more, or 0.1% or more of the water depth of the water W in the breeding aquarium 2. The bottom corresponds to the bottom wall 21 of the breeding aquarium 2.

[0026] The salt supply unit 4 supplies salts to the bottom of the water where a high-concentration region is formed. The salt supply unit 4 may be configured as a pipe, for example, as shown in FIG. 1. In the example shown in FIG. 1, the salt supply unit 4 may be installed so that an inlet 41 is provided above the water W and a discharge outlet 42 is provided at the bottom of the water. When the inlet 41 is provided above the water W, the inlet 41 is located above the water surface. Furthermore, the inlet 41 may have a structure in which the inner diameter becomes wider toward the end to make it easier to add salts.

[0027] In the rearing tank 2, the cephalopod larvae do not float near the bottom of the water, but rather float in a floating region A, which is located, for example, at a height of 20% to 85% of the depth of the water W from the bottom. Therefore, in an aquarium with a water depth of approximately 80 cm to 200 cm, the region 15 cm or less from the bottom where the high concentration region is formed is below the floating region A. When the salt supply unit 4 shown in FIG. 1 is used, the salt supply unit 4 does not open near the floating region A, so salts introduced through the inlet 41 are discharged into the water from the outlet 42 without passing through the floating region A.

[0028] The high-concentration region is an area intermittently provided during the floating rearing period of cephalopod larvae. Therefore, by adding salts to the bottom of the rearing tank 2 during the floating rearing period of cephalopod larvae, an area with a higher salinity than the water in other areas is formed on the bottom of the rearing tank 2. The salinity of the high-concentration region is higher than that of seawater (the water W) introduced into the rearing tank 2, and may be, for example, 40‰ or more, 45‰ or more, 50‰ or more, 55‰ or more, 60‰ or more, 65‰ or more, 70‰ or more, 75‰ or more, 80‰ or more, 85‰ or more, 90‰ or more, 95‰ or more, or 100‰ or more. The salinity can be measured, for example, using an electrical conductivity-type salinity meter. The upper limit of the salt concentration in the high-concentration region is not a problem as long as the salt dissolves, but for example, the salt concentration may be 250‰ or less, 200‰ or less, or 180‰ or less. The high-concentration region may also contain a substance that increases its specific gravity. An example of such a substance is glycerol. Increasing the specific gravity makes it easier for the high-concentration region to remain at the bottom of the breeding tank 2.

[0029] As described above, the cephalopod rearing method using the cephalopod rearing device 1 is a method for rearing cephalopod larvae in the rearing tank 2.

[0030] Here, the cephalopod rearing method using the cephalopod rearing device 1 includes forming a high-concentration region with a higher salt concentration than seawater at the bottom of the rearing tank 2 during the floating rearing period of the cephalopod larvae, and removing the high-concentration region after a predetermined time has passed since the formation of the high-concentration region.

[0031] 2 shows a state in which a high-concentration region S has been formed in the breeding aquarium 2. In the example shown in FIG. 2, salts are supplied to the breeding aquarium 2 using the salt supply unit 4, resulting in the formation of a high-concentration region S at the bottom of the breeding aquarium 2.

[0032] 2 shows a state in which a high-concentration region S is formed by supplying high-concentration salt water from the salt supply unit 4. The high-concentration salt water may contain, for example, at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. The concentration of the high-concentration salt water may be set higher than the salt concentration in the high-concentration region S.

[0033] The salts supplied from the salt supply unit 4 are not limited to high-concentration salt water. For example, the high-concentration region S may be formed by supplying solid salts from the salt supply unit 4. The solid salts may include at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. As described above, the salts supplied from the salt supply unit 4 may include at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

[0034] Furthermore, the salts supplied from the salt supply unit 4 may be a combination of high-concentration salt water and solid salt. When solid salt is added to form the high-concentration region S, the amount of solid salt added may be determined taking into account the salt concentration of the high-concentration region S. For example, if the solid salt is used in granular or powder form, the increased surface area makes it easier to dissolve, making it easier to adjust the salt concentration. As described above, the salt supply unit 4 may supply high-concentration salt water and / or solid salt to the bottom of the breeding aquarium 2. That is, the salt supply unit 4 may supply either high-concentration salt water or solid salt, or both high-concentration salt water and solid salt, to the bottom of the breeding aquarium 2. In other words, the salt supply unit 4 may supply at least one selected from the group consisting of high-concentration salt water and solid salt to the bottom of the breeding aquarium 2.

[0035] The high-concentration region S formed at the bottom of the breeding tank 2 is intended to prevent the occurrence and proliferation of protozoa in the breeding tank 2. Because protozoa can occur and proliferate at the bottom of the breeding tank 2, forming the high-concentration region S at the bottom of the water makes it possible to exterminate the protozoa. The above-mentioned salt concentration is suitable for exterminating protozoa, making it possible to exterminate the protozoa in a relatively short period of time. Furthermore, the high-concentration region S is not formed in the floating region A of the cephalopod larvae, but is formed only at the bottom of the water. Therefore, forming the high-concentration region S prevents the death of not only the protozoa but also the cephalopod larvae.

[0036] Furthermore, this high-concentration region S is removed after a predetermined time has elapsed. When the high-concentration region S is formed in the breeding aquarium 2, the salt content of the high-concentration region S can cause changes in the salt concentration throughout the breeding aquarium 2. Therefore, the high-concentration region S is removed when the eradication of the protozoa has progressed to a certain extent. The predetermined time can be set according to the salt concentration of the high-concentration region S, and may be, for example, 15 minutes or more and 60 minutes or less. In an experimental example, it was confirmed that when protozoa were exposed to saltwater with a salt concentration of 40‰, they could be eradicated in 32 minutes and 40 seconds. From these results, it is believed that maintaining the high-concentration region S for 15 minutes or more can largely eliminate the protozoa in the breeding aquarium 2. On the other hand, setting the period to 60 minutes or less can suppress changes in the salt concentration of the water in the breeding aquarium 2 while reliably eradicating the protozoa. The predetermined time may be 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 33 minutes or more, or 35 minutes or more. Furthermore, there is no problem as long as the high-concentration region S is maintained, but the specified time may be, for example, 180 minutes or less, 150 minutes or less, 120 minutes or less, 100 minutes or less, 80 minutes or less, 60 minutes or less, 50 minutes or less, 40 minutes or less, or 30 minutes or less. If the specified time is too short, protozoa may not be effectively eradicated. If the specified time is too long, the high-concentration region S may not be maintained. Furthermore, if the specified time is too long, the growth of swimming cephalopod larvae may be affected by the high-concentration region S.

[0037] One example of a method for removing the high-concentration region S is to use the salt supply unit 4 to also remove water present in the high-concentration region S. That is, the high-concentration region S can be removed by sucking saltwater from the high-concentration region S through the outlet 42 of the salt supply unit 4 shown in FIG. 2 and discharging it to the outside through the inlet 41. By adjusting the suction speed, for example, water near the high-concentration region S, i.e., at the bottom of the breeding aquarium 2, can be removed. In this way, the salt supply unit 4 can be used as a supply means connecting the outside of the breeding aquarium 2 with the bottom of the breeding aquarium 2, and also as a removal means for removing water present in the high-concentration region S.

[0038] Note that removing the water present in the high-concentration region S may reduce the amount of water in the breeding aquarium 2. In consideration of this, when removing the high-concentration region S, control such as increasing the amount of water injected from the water injection unit 31 may be performed so that the amount of water in the breeding aquarium 2 is maintained.

[0039] The method for removing the high concentration region S may be a method other than the method using the salt supply unit 4 as a removal means. For example, if the drainage unit 32 is provided at the bottom of the water, the drainage unit 32 may be used to remove the water present in the high concentration region S. Also, if solid salt is introduced at the bottom of the water and remains after a predetermined time has elapsed, the solid may be removed first, and then the water near the bottom of the water may be removed.

[0040] Furthermore, water exchange by the water inlet unit 31 and the drainage unit 32 may not be performed while the high-concentration region S is formed at the bottom of the breeding aquarium 2. The water inlet and outlet by the water inlet and outlet units 31 and 32 may move within the breeding aquarium 2, potentially causing the water in the high-concentration region S to mix with the water above it. To avoid this situation, for example, water exchange by the water inlet and outlet units 31 and 32 may be stopped or the control may be changed to minimize the amount of water inlet and outlet. At the same time, the aeration equipment 33 may be stopped or the aeration rate reduced to facilitate maintaining the high-concentration region S. This is because the water in the breeding aquarium 2 becomes more stationary, making it easier to maintain the high-concentration region S. When removing the high-concentration region S, the amount of water removed may be adjusted to the extent that the high-concentration region S can be removed, and additional water may be removed during removal. The high-concentration region S may be colored, for example, with food coloring, so that its removal can be visually confirmed.

[0041] As described above, the cephalopod rearing method using the cephalopod rearing device 1 includes forming a high-concentration region S, which has a higher salt concentration than seawater, at the bottom of the rearing tank 2 during the floating rearing period of the cephalopod larvae, and removing the high-concentration region S after a predetermined time has passed since the formation of the high-concentration region S. Removal of the high-concentration region S includes maintaining the high-concentration region S for a certain period of time and then stirring the entire region to eliminate the high-concentration region S as a whole. By forming the high-concentration region S as described above and removing it after a predetermined time, the mortality rate of the cephalopod larvae in the rearing tank 2 can be reduced.

[0042] During the floating rearing period of cephalopod larvae, the occurrence of protozoa in the aquarium can cause the death of the cephalopod larvae. This is thought to be because the protozoa that have penetrated into the mantle eat the cephalopod larvae. In response to this, by providing a high-concentration area S at the bottom of the rearing aquarium 2, even if protozoa occur in the aquarium, they can be removed.

[0043] The formation and removal of the high-concentration region S may be performed during at least a portion of the period until the cephalopod larvae reach 15 days of age. During the period until the cephalopod larvae reach 15 days of age, death due to the proliferation of protozoa is likely to occur. Furthermore, the protozoa that emerge and proliferate during this period may originate from the saltwater, feed, and the like introduced into the breeding tank 2. Therefore, by forming and removing the high-concentration region S during the period until the cephalopod larvae reach 15 days of age, the risk of emergence and proliferation of protozoa thereafter can be reduced. A series of steps, including the formation and removal of the high-concentration region S, may be performed during at least a portion of the period until the cephalopod larvae reach 15 days of age. The period until the cephalopod larvae reach 15 days of age corresponds to the period from 0 days of age to 15 days of age. In this case, the series of steps may also be performed during at least a portion of the period from 16 days of age onward, or may not be performed during the period from 16 days of age onward.

[0044] Furthermore, the formation and removal of the high-concentration region S may be performed once, or multiple times during the rearing period. During the rearing period of cephalopod larvae, protozoa may emerge and multiply from larval corpses, feed, etc. Therefore, the formation and removal of the high-concentration region S may be performed when a tendency for protozoa multiplication is confirmed. As described above, a series of steps including the formation and removal of the high-concentration region S may be repeated during the rearing period. In other words, a series of steps including the formation and removal of the high-concentration region S may be performed multiple times during the rearing period.

[0045] The bottom of the breeding tank 2 in which the high-concentration region S is provided may be within 5 cm of the deepest part of the breeding tank. The deepest part of the breeding tank is where organic matter, such as dead cephalopod larvae, leftover food, or excrement, which are sources of protozoan development, accumulates or may accumulate. The salinity of the high-concentration region S may be 40‰ or more, 45‰ or more, 50‰ or more, 55‰ or more, 60‰ or more, 65‰ or more, 70‰ or more, 75‰ or more, 80‰ or more, 85‰ or more, 90‰ or more, 95‰ or more, or 100‰ or more. The upper limit of the salinity of the high-concentration region S is not a problem as long as the salt dissolves, but the salinity may be, for example, 250‰ or less, 200‰ or less, or 180‰ or less. In this case, the protozoa can be appropriately removed by setting the salt concentration of the high-concentration region S within the above range. On the other hand, by setting the high-concentration region S within 5 cm from the deepest part of the breeding tank 2, the protozoa can be appropriately removed from the region where they may be present while minimizing the impact on the cephalopod larvae being raised in the breeding tank 2.

[0046] The predetermined time for forming the high-concentration region S may be 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 33 minutes or more, or 35 minutes or more. As long as the high-concentration region S is maintained, there is no problem. The predetermined time may be, for example, 180 minutes or less, 150 minutes or less, 120 minutes or less, 100 minutes or less, 80 minutes or less, 60 minutes or less, 50 minutes or less, 40 minutes or less, or 30 minutes or less. By setting the predetermined time within such a range, protozoa can be appropriately removed during the time when the high-concentration region S is formed.

[0047] Forming the high-concentration region S may include supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank 2. Using solid salt in, for example, granular or powder form increases the surface area. This makes the solid salt more soluble and makes it easier to adjust the salinity. The highly concentrated salt water and / or solid salt may contain at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. Supplying these substances to the bottom of the breeding tank 2 allows the high-concentration region S at the bottom to be appropriately formed.

[0048] Furthermore, to form the high-concentration region S, high-concentration salt water and / or solid salt may be supplied to the bottom of the breeding tank 2 so as not to mix with the water above. In this case, changes in the salinity of the floating region A of cephalopod larvae that may be present above can be suppressed. When using solid salt, for example, if it is a large lump, even if it is added from the top of the breeding tank 2, it will not dissolve much before reaching the bottom, and will gradually dissolve after reaching the bottom, thereby forming the high-concentration region S.

[0049] In forming the high-concentration region S, high-concentration salt water may be supplied using a supply means that connects the outside of the breeding aquarium 2 with the bottom of the breeding aquarium 2. The supply means may also be a pipe such as the salt supply unit 4.

[0050] Furthermore, in removing the high concentration region S, the water present in the high concentration region S may be removed using a removal means that connects the outside of the breeding aquarium 2 to the bottom of the breeding aquarium 2. The removal means may also be a pipe.

[0051] Furthermore, a component that functions as a supply means, such as the salt supply unit 4, may also be used as a removal means for removing water present in the high concentration region S. In this case, the formation and removal of the high concentration region S can be achieved with only one means, preventing the device configuration from becoming complicated. The salt supply unit 4 may be installed when in use and removed when use is finished.

[0052] The cephalopod rearing device 1 and cephalopod rearing method described above can also be considered devices and methods capable of controlling the protozoan density present in the rearing tank 2. That is, the cephalopod rearing device 1 and cephalopod rearing method may control the protozoan density in the water of the rearing tank 2 during the floating rearing period so that the protozoan density is 350 individuals / ml or less. As described above, by forming a high-salinity region S and removing it after a predetermined period of time, protozoa that may remain on the bottom of the water can be eliminated, thereby adjusting the protozoan density in the water to a low level. Therefore, by controlling the protozoan density so that the protozoan density is 350 individuals / ml or less as described above, the proliferation of protozoa can be suppressed, and the mortality rate of cephalopod larvae can be reduced. The protozoan density may be controlled to 300 individuals / ml or less, 315 individuals / ml or less, 350 individuals / ml or less, 400 individuals / ml or less, 450 individuals / ml or less, or 500 individuals / ml or less. This also inhibits protozoan proliferation and reduces the mortality rate of cephalopod larvae. The protozoan density per ml can be calculated by collecting 50 ml of rearing water near the bottom of the rearing tank 2 and visually counting the number of protozoans in 20 μl of the water under a microscope. The mortality rate of octopus larvae can be calculated by counting the number of dead individuals in the water discharged during cleaning and calculating the percentage of the total number of reared individuals.

[0053] When breeding octopuses as cephalopods, protozoa that may occur in the breeding tank 2 include flagellates and ciliates. More specifically, flagellates include Ichthyyobodonecator, and ciliates include Uronemamarinum, Philasterides dicentrarchi, Pseudocohnilembuspersalinus, Pseudorhabdosynochus hargisi, and Metanophrys sinensis. Therefore, when breeding cephalopods using the above-described cephalopod breeding device 1, the protozoa whose protozoa density is to be measured may be flagellates or ciliates. In this case, the protozoa occurrence status in the breeding tank 2 can be more accurately determined.

[0054] [Protozoan Prevention Method] The configuration according to this embodiment can also be referred to as a method for preventing the occurrence of protozoa, i.e., a protozoan prevention method. That is, the method for preventing the occurrence of protozoa using the cephalopod rearing device 1 is a method for preventing the occurrence of protozoa in the rearing tank 2 when rearing cephalopod larvae in the rearing tank 2. In this case, the protozoa whose occurrence is to be prevented are not limited as long as their occurrence can be prevented by treatment with the high-concentration region S, but may be, for example, flagellates or ciliates.

[0055] The method for preventing the occurrence of protozoa includes forming a high-concentration region S, which has a higher salt concentration than seawater, at the bottom of the breeding tank 2 during the floating breeding period of cephalopod larvae, and removing the high-concentration region S after a predetermined time has passed since the formation of the high-concentration region S. As described above, by forming and removing the high-concentration region S in the breeding tank 2, it is possible to eliminate protozoa in the breeding tank 2 and reduce the mortality rate of cephalopod larvae.

[0056] The formation and removal of the high-concentration region S can be carried out during at least part of the rearing period until the cephalopod larvae reach 15 days of age. This is because the number of deaths expected to be caused by the emergence and proliferation of protozoa may increase during the rearing period until the cephalopod larvae reach 15 days of age. Therefore, by forming and removing the high-concentration region S during the above period, the emergence of protozoa can be effectively suppressed.

[0057] Furthermore, the formation and removal of the high-concentration region S may be performed multiple times during the rearing period. During the rearing period of cephalopod larvae, protozoa may occur and multiply due to larval carcasses, feed, etc. Therefore, by performing the above treatment multiple times, the possibility of protozoa occurrence can be further reduced.

[0058] The bottom of the breeding tank 2 in which the high-concentration region S is provided may be within 5 cm of the deepest part of the breeding tank. The salinity in the high-concentration region S may be 40‰ or more, 45‰ or more, 50‰ or more, 55‰ or more, 60‰ or more, 65‰ or more, 70‰ or more, 75‰ or more, 80‰ or more, 85‰ or more, 90‰ or more, 95‰ or more, or 100‰ or more. The salinity can be measured, for example, using an electrical conductivity-type salinity meter. The upper limit of the salinity in the high-concentration region S is not a problem as long as the salt dissolves, but the salinity may be, for example, 250‰ or less, 200‰ or less, or 180‰ or less. By setting the salinity in the high-concentration region S within the above range, the occurrence of protozoa can be appropriately prevented. On the other hand, by placing the high concentration area S within 5 cm from the deepest part of the breeding tank 2, it is possible to prevent the occurrence of protozoa in areas where protozoa may occur, while minimizing the impact on the cephalopod larvae being raised in the breeding tank 2.

[0059] Furthermore, the predetermined time during which the high-concentration region S is formed may be 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 33 minutes or more, or 35 minutes or more. Furthermore, as long as the high-concentration region S is maintained, there is no problem, but the predetermined time may be, for example, 180 minutes or less, 150 minutes or less, 120 minutes or less, 100 minutes or less, 80 minutes or less, 60 minutes or less, 50 minutes or less, 40 minutes or less, or 30 minutes or less. By setting the predetermined time within such a range, it is possible to appropriately prevent the occurrence of protozoa during the time when the high-concentration region S is formed. As an example, the predetermined time may be 15 minutes or more and 60 minutes or less.

[0060] Forming the high-concentration region S may include supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank 2. Using solid salt in, for example, granular or powder form increases the surface area. This makes the solid salt more soluble and makes it easier to adjust the salinity. The highly concentrated salt water and / or solid salt may contain at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. Supplying these substances to the bottom of the breeding tank 2 allows the high-concentration region S at the bottom to be appropriately formed.

[0061] Furthermore, by forming the high-concentration region S, high-concentration salt water and / or solid salt may be supplied to the bottom of the breeding tank 2 so as not to mix with the water above. In this case, changes in the salinity of the floating region A for cephalopod larvae that may be present above can be suppressed, thereby further reducing the impact on the cephalopod larvae.

[0062] In forming the high-concentration region S, high-concentration salt water may be supplied using a supply means that connects the outside of the breeding aquarium 2 with the bottom of the breeding aquarium 2. The supply means may also be a pipe such as the salt supply unit 4.

[0063] Furthermore, in removing the high concentration region S, the water present in the high concentration region S may be removed using a removal means that connects the outside of the breeding aquarium 2 to the bottom of the breeding aquarium 2. The removal means may also be a pipe.

[0064] Furthermore, a member that functions as a supply means, such as the salt supply unit 4, may also be used as a removal means for removing water present in the high-concentration region S. In this case, the formation and removal of the high-concentration region S can be achieved with only one means, which prevents the device configuration from becoming complicated.

[0065] The protozoan prevention method using the cephalopod breeding apparatus 1 can also be described as an apparatus and method capable of controlling the protozoan density present in the breeding tank 2 by forming and removing the high-concentration region S. That is, the protozoan prevention method according to this embodiment may control the protozoan density in the water of the breeding tank 2 during the floating breeding period so that the protozoan density is 300 individuals / ml or less, 315 individuals / ml or less, 350 individuals / ml or less, 400 individuals / ml or less, 450 individuals / ml or less, or 500 individuals / ml or less. As described above, by forming the high-concentration region S with a high salt concentration and removing it after a predetermined period of time, protozoans that may remain at the bottom of the water can be eliminated, thereby adjusting the protozoan density in the water to a low level. Therefore, by controlling the protozoan density so that it falls within the above-described range, the occurrence and proliferation of protozoans can be suppressed.

[0066] [Protozoan Elimination Method] The configuration according to this embodiment can also be called a method for eliminating protozoa in the breeding tank 2, i.e., a protozoan extermination method. In other words, the protozoan extermination method using the cephalopod breeding device 1 is a method for eliminating protozoa from the breeding tank 2 when breeding cephalopod larvae in the breeding tank 2. In this case, the protozoa to be exterminated are not limited as long as they can be exterminated by treatment in the high-concentration region S, but may be, for example, flagellates or ciliates.

[0067] The method for eliminating the protozoa includes forming a high-concentration region S, which has a higher salt concentration than seawater, at the bottom of the breeding tank 2 during the floating breeding period of the cephalopod larvae, and removing the high-concentration region S after a predetermined time has passed since the formation of the high-concentration region S. By forming and removing the high-concentration region S in the breeding tank 2 as described above, it is possible to eliminate the protozoa in the breeding tank 2 and reduce the mortality rate of the cephalopod larvae.

[0068] The formation and removal of the high-concentration region S can be carried out during at least part of the rearing period until the cephalopod larvae reach 15 days of age. This is because the number of deaths expected to be caused by the emergence and proliferation of protozoa can increase during the rearing period until the cephalopod larvae reach 15 days of age. Therefore, by forming and removing the high-concentration region S during the above period, protozoa can be effectively eradicated and their subsequent emergence and proliferation can also be suppressed.

[0069] Furthermore, the formation and removal of the high-concentration region S may be carried out multiple times during the rearing period. During the rearing period of cephalopod larvae, protozoa may emerge and multiply from larval carcasses, feed, etc. Therefore, by carrying out the above treatment multiple times, protozoa can be more effectively eradicated.

[0070] The bottom of the breeding tank 2 in which the high-concentration region S is provided may be within 5 cm of the deepest part of the breeding tank. The salinity in the high-concentration region S may be 40‰ or more, 45‰ or more, 50‰ or more, 55‰ or more, 60‰ or more, 65‰ or more, 70‰ or more, 75‰ or more, 80‰ or more, 85‰ or more, 90‰ or more, 95‰ or more, or 100‰ or more. The salinity can be measured, for example, using an electrical conductivity-type salinity meter. The upper limit of the salinity in the high-concentration region S is not a problem as long as the salt dissolves, but the salinity may be, for example, 250‰ or less, 200‰ or less, or 180‰ or less. By setting the salinity in the high-concentration region S within the above range, protozoa can be appropriately exterminated. On the other hand, by placing the high concentration area S within 5 cm from the deepest part of the breeding tank 2, it is possible to eliminate protozoa in areas where protozoa may occur while minimizing the impact on the cephalopod larvae being raised in the breeding tank 2.

[0071] Furthermore, the predetermined time for forming the high-concentration region S may be 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 33 minutes or more, or 35 minutes or more. Furthermore, as long as the high-concentration region S is maintained, there is no problem, and the predetermined time may be, for example, 180 minutes or less, 150 minutes or less, 120 minutes or less, 100 minutes or less, 80 minutes or less, 60 minutes or less, 50 minutes or less, 40 minutes or less, or 30 minutes or less. By setting the predetermined time within such a range, protozoa in the high-concentration region S can be appropriately exterminated. As an example, the predetermined time may be 15 minutes or more and 60 minutes or less.

[0072] Forming the high-concentration region S may include supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank. For example, if the solid salt is used in granular or powder form, the increased surface area makes it easier to dissolve, making it easier to adjust the salinity. The highly concentrated salt water and / or solid salt may contain at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride. Supplying these substances to the bottom of the breeding tank 2 allows the high-concentration region S at the bottom to be appropriately formed.

[0073] Furthermore, by forming the high-concentration region S, high-concentration salt water and / or solid salt may be supplied to the bottom of the breeding tank 2 so as not to mix with the water above. In this case, changes in the salinity of the floating region A for cephalopod larvae that may be present above can be suppressed, thereby further reducing the impact on the cephalopod larvae.

[0074] In forming the high-concentration region S, high-concentration salt water may be supplied using a supply means that connects the outside of the breeding aquarium 2 with the bottom of the breeding aquarium 2. The supply means may also be a pipe such as the salt supply unit 4.

[0075] Furthermore, in removing the high concentration region S, the water present in the high concentration region S may be removed using a removal means that connects the outside of the breeding aquarium 2 to the bottom of the breeding aquarium 2. The removal means may also be a pipe.

[0076] Furthermore, a member that functions as a supply means, such as the salt supply unit 4, may also be used as a removal means for removing water present in the high-concentration region S. In this case, the formation and removal of the high-concentration region S can be achieved with only one means, which prevents the device configuration from becoming complicated.

[0077] The protozoan extermination method using the cephalopod rearing apparatus 1 can also be described as an apparatus and method capable of controlling the protozoan density present in the rearing tank 2 by forming and removing the high-concentration region S. That is, the protozoan extermination method according to this embodiment may control the protozoan density in the water of the rearing tank 2 during the floating rearing period so that the protozoan density is 300 individuals / ml or less, 315 individuals / ml or less, 350 individuals / ml or less, 400 individuals / ml or less, 450 individuals / ml or less, or 500 individuals / ml or less. As described above, by forming the high-concentration region S with a high salt concentration and removing it after a predetermined period of time, protozoans that may remain at the bottom of the water can be exterminated, thereby adjusting the protozoan density in the water to a low level. Therefore, by controlling the protozoan density so that it falls within the above-described range, the occurrence and proliferation of protozoans can be suppressed.

[0078] Furthermore, the formation and removal of high-concentration regions S can confer protozoan resistance in cephalopod larvae. The formation and removal of high-concentration regions S can impart physiological and / or molecular biological changes related to gene expression to the body of cephalopod larvae during the suspension-rearing period. The formation and removal of high-concentration regions S during the suspension-rearing period of cephalopod larvae can have the effect of suppressing the activity of protozoans that affect the mortality rate of cephalopod larvae. The protozoan resistance acquired by the formation and removal of high-concentration regions S can last for at least 5 days or more, 10 days or more, or 15 days or more.

[0079] Example 1 Using a cephalopod rearing apparatus similar to the cephalopod rearing apparatus 1 shown in Figure 1, octopus larvae, a type of cephalopod, were reared for 12 days. The rearing tank had a capacity of 500 L. The difference from the cephalopod rearing apparatus 1 is that the water inlet section 31 and the drainage section 32 are installed at the bottom of the rearing tank 2. Using this cephalopod rearing apparatus, approximately 3,000 octopus larvae on day 0 after the start of rearing were introduced into the rearing tank 2, and then reared for 12 days.

[0080] During this process, the high-concentration region S was formed and removed five times, depending on the age of the octopus larvae. Specifically, the high-concentration region S was formed and removed on days 0, 3, 6, and 9 after the start of rearing. A 26% aqueous sodium chloride solution was added so that the high-concentration region S was formed. The high-concentration region S was formed at a depth of approximately 3 cm from the water depth in the rearing tank 2, and was removed after being maintained for 15 minutes. The operations for forming and removing the high-concentration region S were all performed in the same way.

[0081] The water exchange unit 3 was controlled so that the water exchange rate in the breeding tank 2 was 77% / day from day 0 to day 6 after the start of breeding, and 100% / day from day 7 onwards. Water exchange was stopped during the time period when the high concentration region S was formed in the breeding tank 2.

[0082] Under the above conditions, the protozoan density and daily mortality rate were measured from day 7 to day 12, and the average was calculated. The results are shown in Table 1. Furthermore, the protozoan that emerged here was examined by 18S rRNA gene sequence analysis, and was confirmed to be Metanophrys sinensis.

[0083] In addition, as Comparative Example 1, octopus larvae were reared under conditions in which the formation and removal of high-concentration regions S was not performed, and the protozoan density and daily mortality rate at each age from day 7 to day 12 were measured and averaged. The results are shown in Table 1.

[0084] According to Table 1, it was confirmed that Example 1 tended to have a lower protozoan density than Comparative Example 1. Furthermore, Example 1 had a lower daily mortality rate than Comparative Example 1. From this, it was confirmed that by forming a high-concentration region S with a high salt concentration, it is possible to lower the protozoan density and also reduce the mortality rate of octopus larvae.

[0085] Example 2: Octopus larvae reared for 12 days while forming and removing high-concentration regions S in Example 1 were reared for an additional 5 days, and approximately 2,000 of them were exposed to an environment where the protozoan density was 350 (individuals / ml), and the daily mortality rate was measured. In Comparative Example 2, octopus larvae reared for 12 days without forming and removing high-concentration regions S were reared for an additional 3 days, and approximately 1,500 of them were exposed to an environment where the protozoan density was 150 (individuals / ml), and the daily mortality rate was measured. The results are shown in Table 2.

[0086]

[0087] According to Table 2, Example 2 had a lower daily mortality rate than Comparative Example 2, even when exposed to a high protozoan density. This confirmed that rearing in a high-salt-concentration region S can reduce the daily mortality rate even when the protozoan density is high. In Example 2, the daily mortality rate was 8.00% or less, even when the protozoan density in the rearing tank water was 150 individuals / ml or more.

[0088] [Modifications] Although the embodiments of the present disclosure have been described above, the cephalopod rearing method, protozoan prevention method, and protozoan extermination method according to the present disclosure are not limited to the above-described embodiments.

[0089] For example, although the above embodiment has been described with respect to a case where the cephalopod is a common octopus, when rearing larvae of other cephalopods, the rearing conditions may be changed as necessary. At least some of the matters described in other examples may be applied to one example among the various examples described in this disclosure.

[0090] 1... Cephalopod breeding device, 2... breeding tank, 3... water exchange section, 4... salt supply section, 31... water injection section, 32... drainage section, 33... aeration equipment, 21... bottom wall, 41... inlet, 42... outlet

Claims

1. A method for rearing cephalopod larvae in a rearing tank, comprising: During the floating rearing period of the cephalopod larvae, forming a high-salinity region at the bottom of the breeding tank, the high-salinity region having a higher salt concentration than seawater; removing the high concentration region after a predetermined time has elapsed since forming the high concentration region; A method for raising cephalopods, including:

2. 2. The method for rearing cephalopods according to claim 1, wherein forming the high concentration area and removing the high concentration area are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age.

3. 2. The method for raising cephalopods according to claim 1, wherein the bottom of the breeding tank is within 5 cm of the deepest part of the breeding tank.

4. The method for raising cephalopods according to claim 1, wherein the salinity in the high concentration region is 40‰ or higher.

5. The method for raising cephalopods according to claim 1 , wherein forming the high-concentration region comprises supplying highly salty water and / or solid salt to the bottom of the breeding tank.

6. The cephalopod rearing method described in claim 5, wherein the highly concentrated salt water and / or the solid salt contains at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

7. The method for raising cephalopods according to claim 5, wherein in forming the high concentration region, the high concentration salt water and / or solid salt is supplied to the bottom of the breeding tank so as not to mix with the water above it.

8. 8. The method for raising cephalopods according to claim 7, wherein the high-concentration saltwater is supplied using a supply means connecting the outside of the breeding aquarium with the bottom of the breeding aquarium, in forming the high-concentration area.

9. The method for raising cephalopods according to claim 8, wherein the supply means is a pipe.

10. The method for raising cephalopods according to claim 8 , wherein in removing the high concentration area, the supply means is used as a removal means for removing water present in the high concentration area.

11. The cephalopod rearing method according to any one of claims 1 to 10, wherein the predetermined time is 15 minutes or more and 60 minutes or less.

12. The cephalopod rearing method according to any one of claims 1 to 10, wherein in removing the high concentration area, water present in the high concentration area is removed using a removal means connecting the outside of the breeding aquarium to the bottom of the breeding aquarium.

13. The method for raising cephalopods according to claim 12, wherein the removal means is a pipe.

14. The cephalopod rearing method according to any one of claims 1 to 10, wherein forming the high concentration area and removing the high concentration area are performed multiple times during the rearing period of the cephalopod larvae.

15. During the floating rearing period of the cephalopod larvae, The method for raising cephalopods according to any one of claims 1 to 10, wherein the protozoan density in the water of the breeding tank is controlled to be 350 individuals / ml or less.

16. The method for rearing cephalopods according to claim 15, wherein the protozoa to be measured for protozoan density are flagellates or ciliates.

17. A method for rearing cephalopod larvae in a rearing tank, comprising: During the floating rearing period of the cephalopod larvae, A method for raising cephalopods, comprising controlling the protozoan density in the water of the breeding tank to 350 individuals / ml or less.

18. The method for rearing cephalopods according to claim 17, wherein the protozoa to be measured for protozoan density are flagellates or ciliates.

19. A method for preventing the occurrence of protozoa in a breeding tank when breeding cephalopod larvae in the breeding tank, comprising: During the floating rearing period of the cephalopod larvae, forming a high-salinity region at the bottom of the breeding tank, the high-salinity region having a higher salt concentration than seawater; removing the high concentration region after a predetermined time has elapsed since forming the high concentration region; A method for preventing protozoa, comprising:

20. The method for preventing protozoa according to claim 19, wherein forming the high concentration area and removing the high concentration area are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age.

21. 20. The protozoan prevention method according to claim 19, wherein the bottom of the breeding aquarium is within 5 cm of the deepest part of the breeding aquarium.

22. The method for preventing protozoa according to claim 19, wherein the salt concentration in the high-concentration region is 40‰ or more.

23. 20. The method for preventing protozoa according to claim 19, wherein forming the high-concentration region comprises supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank.

24. The method for preventing protozoa according to claim 23, wherein the highly concentrated salt water and / or the solid salt contains at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

25. 24. The method for preventing protozoa according to claim 23, wherein in forming the high-concentration region, the high-concentration salt water and / or solid salt is supplied to the bottom of the breeding aquarium so as not to mix with the water above it.

26. 26. The protozoan prevention method according to claim 25, wherein in forming the high-concentration region, the high-concentration salt water is supplied using a supply means connecting the outside of the breeding aquarium with a bottom of the breeding aquarium.

27. The method for preventing protozoa according to claim 26, wherein the supply means is a pipe.

28. The method for preventing protozoa according to claim 26, wherein in removing the high concentration region, the supplying means is used as a removing means for removing water present in the high concentration region.

29. The protozoan prevention method according to any one of claims 19 to 28, wherein the predetermined time is 15 minutes or more and 60 minutes or less.

30. The protozoan prevention method according to any one of claims 19 to 28, wherein in removing the high concentration area, water present in the high concentration area is removed using a removal means that connects the outside of the breeding aquarium with the bottom of the breeding aquarium.

31. The protozoan prevention method according to claim 30, wherein the removal means is a pipe.

32. The protozoan prevention method according to any one of claims 19 to 28, wherein forming the high-concentration area and removing the high-concentration area are carried out multiple times during the rearing period of the cephalopod larvae.

33. The method for preventing protozoa according to any one of claims 19 to 28, wherein the protozoa is a flagellate or a ciliate.

34. The protozoan prevention method according to any one of claims 19 to 28, wherein the protozoan density in the water of the breeding tank during the floating breeding period is controlled to be 350 individuals / ml or less.

35. A method for eliminating protozoa from a breeding tank when breeding cephalopod larvae in the breeding tank, comprising: During the floating rearing period of the cephalopod larvae, forming a high-salinity region at the bottom of the breeding tank, the high-salinity region having a higher salt concentration than seawater; removing the high concentration region after a predetermined time has elapsed since forming the high concentration region; A method for eliminating protozoa, comprising:

36. The protozoan control method according to claim 35, wherein forming the high concentration area and removing the high concentration area are carried out for at least a portion of the period until the cephalopod larvae reach 15 days of age.

37. 36. The protozoan control method according to claim 35, wherein the bottom of the breeding tank is within 5 cm of the deepest part of the breeding tank.

38. The protozoan control method according to claim 35, wherein the salt concentration in the high concentration region is 40‰ or more.

39. The protozoan control method according to claim 35, wherein forming the high concentration region includes supplying highly concentrated salt water and / or solid salt to the bottom of the breeding tank.

40. The protozoan control method according to claim 39, wherein the highly concentrated salt water and / or the solid salt contains at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

41. 40. The protozoan control method according to claim 39, wherein in forming the high concentration region, the high concentration salt water and / or solid salt is supplied to the bottom so as not to mix with the water above the breeding aquarium.

42. 42. The protozoan extermination method according to claim 41, wherein in forming the high concentration region, the high concentration salt water is supplied using a supply means that connects the outside of the breeding aquarium with the bottom of the breeding aquarium.

43. The protozoan control method according to claim 42, wherein the supply means is a pipe.

44. The protozoan control method according to claim 42, wherein in removing the high concentration region, the supply means is used as a removal means for removing water present in the high concentration region.

45. The protozoan control method according to any one of claims 35 to 44, wherein the predetermined time is 15 minutes or more and 60 minutes or less.

46. The protozoan control method according to any one of claims 35 to 44, wherein in removing the high concentration area, water present in the high concentration area is removed using a removal means that connects the outside of the breeding aquarium with the bottom of the breeding aquarium.

47. The protozoan control method according to claim 46, wherein the removal means is piping.

48. The protozoan control method according to any one of claims 35 to 44, wherein forming the high concentration area and removing the high concentration area are carried out multiple times during the rearing period of the cephalopod larvae.

49. The protozoan control method according to any one of claims 35 to 44, wherein the protozoan is a flagellate or a ciliate.

50. The protozoan control method according to any one of claims 35 to 44, wherein the protozoan density in the water of the breeding tank during the floating breeding period is controlled to be 350 individuals / ml or less.

51. Cephalopod larvae are reared in a breeding tank by a rearing method that includes forming a high-concentration region at the bottom of the breeding tank during the floating rearing period of the cephalopod larvae, the high-concentration region having a higher salt concentration than seawater, and removing the high-concentration region after a predetermined time has passed since the formation of the high-concentration region.

52. 52. The cephalopod larvae of claim 51, wherein forming the high concentration areas and removing the high concentration areas are performed for at least a portion of the time until the cephalopod larvae are 15 days old.

53. 52. The cephalopod larvae of claim 51, wherein the bottom of the rearing tank is within 5 cm of the deepest point of the rearing tank.

54. 52. The cephalopod larvae of claim 51, wherein the salinity in the high concentration region is 40‰ or more.

55. 52. The cephalopod larvae of claim 51, wherein forming the high concentration region comprises providing high salt concentration water and / or solid salt to the bottom of the rearing tank.

56. 56. The cephalopod larvae of claim 55, wherein the highly salty water and / or the solid salt comprises at least one salt selected from the group consisting of sodium chloride, potassium chloride, magnesium chloride, magnesium sulfate, calcium sulfate, and calcium chloride.

57. 56. The cephalopod larvae of claim 55, wherein in forming the high concentration region, the high concentration salt water and / or solid salt is supplied to the bottom so as not to mix with the water above the rearing tank.

58. 58. The cephalopod larvae of claim 57, wherein the formation of the high-concentration region involves supplying the high-concentration salt water using a supply means connecting the outside of the breeding tank with the bottom of the breeding tank.

59. 59. The cephalopod larvae of claim 58, wherein the supply means is piping.

60. 59. The cephalopod larvae of claim 58, wherein in removing the high concentration area, the supply means is used as a removal means for removing water present in the high concentration area.

61. The cephalopod larvae according to any one of claims 51 to 60, wherein the predetermined time is 15 minutes or more and 60 minutes or less.

62. In removing the high concentration area, water present in the high concentration area is removed using a removal means connecting the outside of the breeding aquarium and the bottom of the breeding aquarium. Cephalopod larvae according to any one of claims 51 to 60.

63. 63. The cephalopod larvae of claim 62, wherein the removal means is tubing.

64. The cephalopod larvae according to any one of claims 51 to 60, wherein forming the high concentration area and removing the high concentration area are carried out multiple times during the rearing period of the cephalopod larvae.

65. Protozoan-resistant cephalopod larvae.

66. 66. The cephalopod larva of claim 65, wherein the protozoan is a flagellate or a ciliate.

67. 67. Cephalopod larvae are reared in a breeding tank, and are reared by a rearing method that includes forming a high-concentration region having a higher salt concentration than seawater at the bottom of the breeding tank during a floating breeding period of the cephalopod larvae, and removing the high-concentration region after a predetermined time has elapsed since the formation of the high-concentration region, wherein, during the floating breeding period of the cephalopod larvae, even if the protozoan density in the water of the breeding tank is 150 individuals / ml or more, the daily mortality rate is 8.00 or less.

68. Cephalopod larvae according to claim 65 or claim 66.

68. 68. The cephalopod larvae of claim 67, wherein the formation of the high concentration region is performed one or more times.