Closed-loop aquaculture methods for fish

Abstract

The present invention aims to provide a closed-loop land-based aquaculture method for fish that can improve investment efficiency and also improve the rate of nitrate removal. [Solution] A closed-circuit land-based aquaculture method for farming fish on land using seawater or artificial seawater, wherein the rearing water in the rearing tank is circulated through a circulation path, the rearing water is purified as it passes through the circulation path, and the rearing water temperature is controlled to 19°C or lower, and the closed-circuit land-based aquaculture method is characterized by forming a section in the upper layer of the rearing water in the rearing tank with a partition wall that prevents fish from entering, and cultivating Ulva prolifera in the section.

Description

Detailed Description of the Invention

Technical Field

[0001] The present invention relates to a method for closed - loop land - based aquaculture of fish.

Background Art

[0002] In recent years, the land - based aquaculture of marine fish has been on the rise. Land - based aquaculture is to culture fish and shellfish in a breeding water tank installed on land, and there are the flow - through type and the closed - loop type. In the flow - through type, fresh breeding water is continuously drawn from the sea or the like to maintain a good breeding environment, while in the closed - loop type, the breeding water is purified by water treatment equipment and recycled to maintain a good breeding environment.

[0003] The water treatment equipment usually consists of a sedimentation tank for removing feces and feed residues, a physical filtration device for removing fine particles, a biological filtration device for nitrifying and detoxifying ammonia, and an ultraviolet irradiation device for sterilizing the breeding water. Furthermore, the closed - loop type is equipped with a water temperature control device for maintaining the suitable water temperature of fish and shellfish, an oxygen dissolution device for increasing the breeding density, a pump for circulating and flowing the breeding water, a blower for aerating the breeding water, etc. (see, for example, Patent Document 1).

[0004] The closed - loop type has advantages such as the installation location is not restricted, the breeding environment can be artificially controlled so that the productivity is high throughout the year, and the drainage volume is small so that the environmental load is small. However, although the productivity is high and the sales revenue is large, there are disadvantages that the initial cost and running cost are high and the investment efficiency is low.

[0005] Also, in order to reduce nitrate ions derived from feces and residual feed in the breeding water, it is necessary to install a denitrification tank for gasifying nitrate ions into nitrogen gas, or to perform treatments such as changing 1 - 5% of the breeding water every day according to the nitrate ion concentration.

[0006] Meanwhile, the present inventors previously proposed a land-based aquaculture apparatus utilizing the filamentous alga *Hibimido* for water purification in rearing water. *Hibimido* utilizes organic matter, nitrate ions, ammonia, and phosphate to promote growth, and when it is separated and harvested from rearing water, the water is purified. While improved profitability could be expected if *Hibimido* could be sold at a high price, it is not recognized as a food product, making its sale extremely difficult. (Patent Document 2)

[0007] Suji-aonori is recognized as having the best aroma among seaweeds, resulting in higher demand and a higher price compared to other types of seaweed. However, like Hibimidoro, Suji-aonori has a tendency to mature quickly and stop elongating its filamentous thallus when the cultivation water temperature exceeds 20°C, drastically reducing the harvest. Suji-aonori was cultivated in the brackish water areas near the mouths of the Yoshino and Shimanto Rivers, but in recent years, possibly due to the effects of global warming, water temperatures have risen, drastically reducing the harvest. In response to this situation, land-based cultivation of Suji-aonori is also increasing. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 3769680 [Patent Document 2] Problems that the invention of Japanese Patent Publication No. 5-30879 aims to solve

[0008] The present invention aims to provide a closed-loop land-based aquaculture method for fish that can improve investment efficiency and also improve the nitrate removal rate.

[0009] The present invention is a closed-circuit land-based aquaculture method for cultivating fish on land using seawater or artificial seawater, characterized in that the rearing water in a rearing tank is circulated through a circulation path, the rearing water is purified as it passes through the circulation path, and the rearing water temperature is controlled to 19°C or lower, and a partition wall is formed in the upper layer of the rearing water in the rearing tank to prevent fish from entering, and Ulva prolifera is cultivated in the partition wall. The present invention is a closed-circuit land-based aquaculture method characterized in that, as described in claim 1, the rearing water in a rearing tank is circulated through a circulation path, the rearing water is purified as it passes through the circulation path, and the rearing water temperature is controlled to 19°C or lower, and a partition wall is formed in the upper layer of the rearing water in the rearing tank to prevent fish from entering, and Ulva prolifera is cultivated in the partition wall. This is a closed-circuit land-based aquaculture method characterized by the propagation of *Prolifera*. Effects of the invention

[0010] The effects of the invention described in claim 1 include the cultivation and production of the expensive *Ulva perforata*, which can be harvested stably by cultivating it at a rearing water temperature of 19°C or lower, using facilities for raising fish. This allows for increased sales and improved investment efficiency without requiring significant investment in new land or equipment. Furthermore, the proliferation of algae reduces nitrate ions in the rearing water, resulting in cost reductions such as a reduction in the size of the denitrification tank where nitrate ions are converted into molecular nitrogen gas by denitrifying bacteria, or a reduction in the proportion of fresh rearing water added (water change rate) to lower the nitrate ion concentration.

[0011] The effects of the invention described in claim 2 include the ability to combine cold-water fish such as salmon or mackerel, which exhibit stable and high growth at water temperatures of 19°C or below, with the expensive *Ulva lactuca*, which can be harvested stably when cultivated at water temperatures of 19°C or below, and to cultivate *Ulva lactuca* using fish rearing equipment. This allows for the production of *Ulva lactuca* without significant investment in new land or equipment, thereby increasing sales. Furthermore, since cold-water fish such as salmon or mackerel are farmed at optimal temperatures, fish sales can also be maximized, improving investment efficiency. In addition, the proliferation of algae reduces nitrate ions in the rearing water, resulting in cost reductions such as the reduction in the size of the denitrification tank where nitrate ions are converted into molecular nitrogen gas by denitrifying bacteria, or a reduction in the proportion of fresh rearing water added (water change rate) to lower the nitrate ion concentration. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic diagram showing one embodiment of this closed-loop land-based aquaculture method. [Figure 2] Figure 2 is a longitudinal cross-sectional view showing one embodiment of the algae cultivation basket 7 in Figure 1. [Figure 3] Figure 3 is a plan view showing an example of the arrangement of algae cultivation baskets 7 in the upper layer of the rearing tank 1. [Modes for carrying out the invention]

[0013] The embodiments of the present invention will be described in detail below with reference to the drawings. Figure 1 is a schematic diagram illustrating one embodiment of the method of the present invention. This embodiment relates to a method for cultivating cold-water fish such as salmon or mackerel using a closed-loop land-based aquaculture apparatus.

[0014] This closed-circuit land-based aquaculture apparatus comprises a rearing tank 1, a sedimentation tank 2 for removing feces and feed residue, a biological filtration system 3 for nitrifying and detoxifying ammonia, an ultraviolet irradiation system 4 for sterilizing rearing water, a water temperature control system 6 for maintaining a suitable water temperature for fish and shellfish, and an oxygen generation and mixing system 5 for increasing rearing density. This closed-circuit land-based aquaculture method is a closed-circuit system in which the rearing water in the rearing tank 1 is passed sequentially through these systems and returned to the rearing tank. Furthermore, a compartment is formed in the upper layer of the rearing water in the rearing tank 1 by a partition wall to prevent fish from entering, and Ulva prolifera is cultivated in this compartment.

[0015] Aquarium 1 contains aquarium water and fish. Aquarium water containing feces and leftover food is drawn from the bottom of aquarium 1 and sent to sedimentation tank 2. Aquarium water containing a high concentration of feces and leftover food (hereinafter referred to as sludge) is drawn from the bottom of sedimentation tank 2 and disposed of as waste or compost material. Aquarium water from which feces and leftover food have been removed is drawn from the top of sedimentation tank 2 and sent to biological filtration tank 3. In biological filtration tank 3, nitrifying bacteria convert ammonia, which is harmful to fish, into nitrate ions, which are harmless to fish, and also remove organic matter and fine solid matter, thus purifying the aquarium water. The aquarium water flowing out of biological filtration tank 3 is sent to ultraviolet irradiation device 4 for sterilization. The water flowing out of ultraviolet irradiation device 4 is sent to oxygen dissolver 5 and oxygen-enriched by oxygen gas aeration, enabling high-density fish rearing. The water flowing out of oxygen dissolver 5 is sent to water temperature controller 6 and the water temperature is adjusted so that the aquarium water temperature in aquarium 1 is 19°C or lower. The water flowing out of the water temperature regulator 6 is sent to the breeding tank 1.

[0016] The upper layer of the rearing tank 1 is equipped with an algae cultivation cage 7, which prevents fish from entering and forms a section for cultivating the sea lettuce. The water flowing out from the water temperature controller 6 is sprayed from above the algae cultivation container 7 and sent to the rearing tank 1. The sea lettuce in the algae cultivation container 7 absorbs phosphorus compounds such as phosphate and nitrogen compounds such as nitrate ions in the rearing water and grows. In this way, phosphorus compounds and nitrogen compounds are removed from the rearing water, and the rearing water is purified.

[0017] During the breeding period, about 1 to 5% of the total water volume is replenished to the breeding tank 1 per day, and the replenished water is discharged from the biological filtration tank. This prevents the accumulation of nitrate, which is the final product of nitrifying bacteria, to a harmful level (600 mg / L or more) for the bred fish.

[0018] The breeding tank 1 is cylindrical or polygonal. The bottom of the tank has an inclination of about 1 / 15 so that feces, uneaten feed, etc. gather in the central part of the tank. The feces, uneaten feed, and breeding water are discharged from the discharge port at the bottom of the tank. A net is attached to the discharge port to prevent the fish being bred from being sucked in.

[0019] The sedimentation tank 2 is cylindrical, and the inlet for the drainage (breeding water) from the breeding tank 1 is provided at the lower part of the cylinder, and the feces and uneaten feed settle downward from here. A discharge cock is provided at the bottom of the sedimentation tank 2 so that the sediment sludge composed of feces and uneaten feed can be discharged, and the sludge is taken out from here and disposed of by waste or composting, etc. The breeding water from which the sludge has been removed is discharged from the water outlet provided on the upper side wall of the sedimentation tank 3 and sent to the biological filtration tank 3.

[0020] The biological filtration tank 3 is filled with filter media for removing fine solids and immobilizing nitrifying bacteria. Due to the action of the nitrifying bacteria immobilized on the filter media, the highly toxic ammonia in fish excrement is oxidized to the less toxic nitrate via nitrite. The size of the biological filtration tank 3, the required amount of filter media, etc. can be easily determined by a person skilled in the art in consideration of the size and number of fish bred in the breeding tank 1, etc.

[0021] The breeding water from the biological filtration tank 3 sent to the ultraviolet irradiation device 4 is sterilized by receiving ultraviolet irradiation. At the same time, the decomposition of the organic matter dissolved in the breeding water is also carried out to a lower molecular weight, which also contributes to the purification of the breeding water.

[0022] Next, the culture water is sent to the oxygen dissolver 5. Here, the oxygen concentration in the culture water is increased using pure oxygen vented from a liquid oxygen cylinder. The ventilation volume is adjusted so that the oxygen saturation of the culture water discharged from the drain outlet of the oxygen dissolver 5 is 70 to 80%. In the ultra-high density culture of fish, in order to maintain such a high oxygen saturation, in the conventional method using air by a blower, the ventilation volume becomes extremely large, and much more energy input is required than the method using pure oxygen.

[0023] Next, the culture water is sent to the water temperature regulator 6. As the water temperature regulator 6, a waste heat recovery type heat pump capable of simultaneously taking out cold and warm water can be used. It is preferable to set the water temperature of the culture tank 1 to be 10°C or higher and 19°C or lower, and more preferably to be 14°C or higher and 17°C or lower.

[0024] In the present invention, the fish cultured are preferably cold-water fish such as salmon or mackerel. Examples of the salmon to be cultured include trout salmon, silver salmon, cherry salmon, early summer salmon, so-called salmon, king salmon, and Atlantic salmon. These cold-water fish have a reduced feed efficiency and health condition at water temperatures exceeding 19°C. As described above, the culture water temperature is preferably 10°C or higher and 19°C or lower, and more preferably 14°C or higher and 17°C or lower.

[0025] The suji aonori used in the present invention is a filamentous alga belonging to the genus Aosa of the family Aosaceae in the class Chlorophyceae. It is also possible to use other Aosa, usuba aonori, hira aonori, and bow aonori of the same genus, but these have a flat string-like or leaf-like thallus, and are more likely to adhere to each other than the filamentous suji aonori, and are less likely to dry.

[0026] Fig. 2 shows an example of the algae cultivation basket 7 in the culture tank 1. The algae cultivation basket 7 is a plastic basket and has a float 10. The part below the float 10 is immersed in the culture water. A rope 11 for attaching and growing suji aonori 13 is stretched below the float 10.

[0027] Such algae cultivation containers 7 are preferably of a weight and size that allows one person to move them. They are easy to set up and remove. As shown in Figure 3, a number of algae cultivation baskets 7 are laid out on the surface of the water in the cultivation tank 1, leaving space for movement. The laid out algae cultivation baskets 7 are connected sequentially by detachable connectors 8. This allows the algae cultivation baskets 7 to be pulled out one by one, making it easy to harvest the algae.

[0028] Above the algae cultivation basket 7, there is a sprinkler pipe 9 with fine pores for spraying water onto the water surface inside the algae cultivation basket 7. This sprinkler pipe is a tube that sends cultivation water from the water temperature controller 6 to the cultivation tank 1. This sprinkling has effects such as promoting algae growth by supplying sufficient nutrients to the green algae and promoting algae growth by stirring the water inside the algae cultivation basket 7.

[0029] One known method for attaching the *Ulva lactuca* 13 to the rope 11 is the mother algae shredding method. First, the mother algae is shredded into 1 to 5 mm pieces using a blender. These shredded pieces are then placed in a container filled with low-concentration seawater, which is seawater diluted twice with fresh water, and cultured. As the shredded pieces mature, migratory cells are released. The rope 11 is then immersed in this low-concentration seawater in the container from which the migratory cells have been released, allowing the migratory cells to attach to the rope 11. The rope 11 with the attached migratory cells is then attached to the algae cultivation cage 7 to allow the *Ulva lactuca* 13 to elongate and grow. Multiple ropes 11 may be attached to a single algae cultivation cage 7.

[0030] The rearing water used in this invention is seawater, seawater diluted with freshwater, or artificial seawater. In the case of seawater, with a raw water salt concentration of 3.5%, a dilution of 5 times the raw water is preferable, and a dilution of 3 times to 4 times the raw water is even more preferable. In the case of artificial seawater, with a raw water salt concentration of 3.5% in the case of seawater, artificial seawater equivalent to a dilution of 5 times the raw water is preferable, and artificial seawater equivalent to a dilution of 3 times to 4 times the raw water is even more preferable. The above rearing water is suitable for the growth of salmon, mackerel, and green laver.

[0031] The above describes one embodiment of a closed-loop land-based aquaculture system for salmon or mackerel, which are cold-water fish. However, other fish besides salmon or mackerel, which are cold-water fish, can also be farmed on land in a similar manner. However, when non-cold-water fish are farmed at water temperatures below 19°C, the growth rate is low, making it difficult to maximize sales. [Industrial applicability]

[0032] As described above, the aquaculture method according to this invention can be used for closed-loop land-based aquaculture of marine fish, especially salmon or mackerel. This method can be used not only in newly constructed closed-loop land-based aquaculture systems, but also in existing closed-loop land-based aquaculture systems simply by attaching the algae cultivation cages 7. [Explanation of symbols]

[0033] 1 is the rearing tank, 2 is the sedimentation tank, 3 is the biological filtration tank, 4 is the ultraviolet irradiation device, 5 is the oxygen dissolver, 6 is the water temperature controller, 7 is the algae cultivation basket, 8 is the connector, 9 is the sprinkler pipe, 10 is the float, 11 is the rope, 12 and the dashed arrow indicate watering, and 13 shows the algae of *Ulva lactuca*.

Claims

1. A closed-circuit land-based aquaculture method for cultivating fish on land using seawater or artificial seawater, wherein the rearing water in the rearing tank is circulated through a circulation path, the rearing water is purified as it passes through the circulation path, and the rearing water temperature is controlled to 19°C or lower, characterized in that a compartment is formed in the upper layer of the rearing water in the rearing tank by a partition wall to prevent fish from entering, and Ulva prophila is cultivated in the compartment.

2. The closed-circuit land-based aquaculture method according to claim 1, characterized in that the fish are cold-water fish such as salmon or mackerel.

3. The closed-circulation land-based aquaculture method according to claim 1 or 2, characterized in that the aforementioned section is a plurality of cages floating near the water surface of the rearing tank 1, and the aforementioned green algae is propagated in the rearing water inside the cages.

4. The closed-circulation land-based aquaculture method according to claim 1, 2, or 3, characterized in that the plurality of cages are sequentially connected.

5. The closed-circulation land-based aquaculture method according to claim 1, 2, 3, or 4, characterized in that the purified rearing water, which has passed through the circulation path, is returned to the rearing tank 1 by being sprayed onto the water surface in the plurality of baskets.

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