JP7558873B2 - Shellfish farming system and shellfish farming method - Google Patents

Description

The present invention relates to a shellfish farming system and a shellfish farming method.

It is known to use materials consisting of calcium silicate-containing granules to promote the growth of shellfish.
As an example, Patent Document 1 describes a shellfish growth promoter consisting of calcium silicate-containing granules, characterized in that, of the total granules constituting the calcium silicate-containing granules, the proportion of granules having a particle size of less than 1 mm is 12 mass% or less, the proportion of granules having a particle size of 1 to 3 mm is 10 to 80 mass%, the proportion of granules having a particle size of more than 3 mm and not more than 4 mm is 10 to 80 mass%, and the proportion of granules having a particle size of more than 4 mm is 12 mass% or less.
Furthermore, Patent Document 1 describes a method for promoting the growth of shellfish, which is characterized by mixing the above-mentioned shellfish growth promoter into bottom sediment.

As another example, Patent Document 2 describes a shellfish farming system that includes an algae culture tank for cultivating algae, a shellfish farming tank for cultivating the shellfish by accommodating the algae cultivated in the algae culture tank, shellfish, a calcium silicate-containing material, and farming water, and a pipeline for supplying the algae from the algae culture tank to the shellfish farming tank.

JP 2019-62775 A JP 2020-156404 A

When using the shellfish growth promotion method described in Patent Document 1, when recovering the grown shellfish, it is necessary to perform an operation of recovering the shellfish from the bottom sediment and the shellfish growth promotion material.
When using the shellfish farming system described in Patent Document 2, it is necessary to manage the water quality in each of the algae culture tanks and shellfish farming tanks.
The object of the present invention is to provide a shellfish farming system that can easily farm shellfish in a good environment without using equipment that requires management, and that can easily recover the grown shellfish in a short period of time, and a shellfish farming method using said system.

As a result of intensive research into solving the above-mentioned problems, the inventors have discovered that the above-mentioned object can be achieved by a shellfish farming system comprising a bag-shaped or basket-shaped net member and calcium silicate-containing granular material contained within the net member, wherein the calcium silicate-containing granular material comprises granules having a particle size larger than the mesh openings of the net member, and have completed the present invention.
The present invention provides the following [1] to [6].

[1] A shellfish farming system comprising a bag-shaped or basket-shaped net member and calcium silicate-containing granular material contained within the net member, characterized in that the calcium silicate-containing granular material includes granules having a particle size larger than the mesh openings of the net member.
[2] The shellfish farming system described in [1] above, wherein the mesh size of the net member is 0.1 to 3 mm.
[3] The shellfish farming system described in [1] or [2] above, wherein the calcium silicate-containing granular material contains granules having a particle size larger than the mesh opening of the net member in a proportion of 50% by mass or more, and does not contain granules having a particle size more than four times the mesh opening of the net member or contains them in a proportion of 50% by mass or less.
[4] The shellfish farming system according to any one of [1] to [3] above, wherein the calcium silicate-containing granules are made of a porous material containing one or more selected from the group consisting of tobermorite, xonotlite, CSH gel, foshagite, gyrolite, hillebrandite, and wollastonite.
[5] The shellfish farming system according to any one of [1] to [4], wherein the calcium silicate-containing granules include aggregates having a maximum particle size of 500 μm or less.
[6] A shellfish farming method using the shellfish farming system described in any one of [1] to [5] above, comprising: an installation step of installing the shellfish farming system in a water area where shellfish live; and a recovery step of recovering the juvenile or adult shellfish from the shellfish farming system when the shellfish larvae settle on the calcium silicate-containing granules and then grow into juvenile or adult shellfish that are larger than the mesh openings of the netting member.

According to the present invention, shellfish can be easily cultured in a good environment without using any equipment that requires maintenance.
Furthermore, according to the present invention, grown shellfish can be easily collected in a short period of time.

The shellfish farming system of the present invention is a shellfish farming system comprising a bag-shaped or cage-shaped net member and calcium silicate-containing granular material contained within the net member, wherein the calcium silicate-containing granular material comprises granules having a particle size larger than the mesh openings of the net member.
In this specification, the term "bag-like" refers to a flexible container capable of housing shellfish (for example, made of synthetic resin and capable of being folded or otherwise reshaped).
"Basket-shaped" refers to a container that does not have the flexibility to accommodate shellfish (for example, one made of synthetic resin that cannot be folded or otherwise reshaped).
"Net member" means a member having mesh that allows free entry and exit of seawater, brackish water or fresh water in the waters where shellfish live.

The calcium silicate-containing granules used in the present invention are granules made of a material containing a compound containing a silicic acid component and a calcium component (calcium silicate-containing material; mainly consisting of calcium silicate hydrate).
Examples of calcium silicate-containing materials include cement paste, cement mortar (in other words, mortar or the mortar portion that constitutes concrete), and materials other than cement paste and cement mortar.
Examples of compounds containing a silicate component and a calcium component in materials other than cement paste and cement mortar include tobermorite, xonotlite, CSH gel, fossiagite, gyrolite, hillebrandite, and wollastonite.

Tobermorite is _a crystalline calcium silicate _hydrate having a chemical composition such as _Ca5 .( _{Si6O18H2 ) 4H2O} (plate-like form), _{Ca5 .} ( _{Si6O18H2 )} (plate-like form), and _{Ca5 .} ( _Si6O18H2 ) _8H2O (fibrous form).
Xonotlite is a crystalline calcium _silicate hydrate having a chemical composition of _Ca6 .( _Si6O17 ).(OH) ₂ (fibrous form) or the like.
CSH gel has a chemical composition of _{αCaO.βSiO2.γH2O} (where α/β=0.7-2.3, _γ /β= _1.2-2.7 ).Specific examples include calcium silicate hydrates having a chemical composition of _{3CaO.2SiO2.3H2O} .
Foshagite has the chemical composition _Ca4 ( _SiO3 ) ₃ (OH) ₂ .
Gyrolite has a chemical composition of ( _NaCa2 ) _Ca14 ( _Si23Al ) _O60 (OH) _8.14H2O or _the like.
_{Hillebrandite} has the chemical composition _Ca2SiO3 (OH) ₂ .
Wollastonite has a chemical composition of CaO.SiO ₂ (fibrous or columnar form) and the like.
Among these, tobermorite is preferred from the viewpoints of the physical properties of the material and the solubility (ease of disintegration) in seawater or the like.

As calcium silicate-containing granular materials made of materials other than cement paste and cement mortar, building materials containing calcium silicate hydrate (especially scraps and waste materials), such as lightweight aerated concrete (ALC), a material whose main component is tobermorite, and moisturizing materials containing xonotlite, may be used.
Among these, it is preferable to use aerated lightweight concrete (ALC) from the viewpoints of availability and economy.
Also, from the viewpoint of promoting the utilization of waste, it is more preferable to use scraps of lightweight aerated concrete generated during the manufacturing process of lightweight aerated concrete or at construction sites.

The lightweight cellular concrete is made of tobermorite and unreacted silica, and has a porosity of about 80% by volume, where porosity refers to the ratio of the total volume of voids to the total volume of concrete.
The proportion of tobermorite in the lightweight aerated concrete is 65 to 80 volume %, with the entire solid phase excluding the voids inside the lightweight aerated concrete being taken as 100 volume %.
Lightweight cellular concrete contains particles of unreacted silica that do not dissolve (disintegrate) (also referred to in this specification as "unreacted silica derived from raw materials").
The unreacted silica derived from the raw materials maintains the strength of the calcium silicate-containing granules used in the present invention and inhibits the granules from easily disintegrating.
Lightweight cellular concrete can be obtained, for example, by autoclaving raw materials (for example, a hardened body consisting of a mixture of these) containing silica powder, cement, quicklime powder, a foaming agent (for example, aluminum powder), water, etc.

The calcium silicate-containing granules are preferably porous. In this case, when the calcium silicate-containing granules are submerged in seawater or the like, the air present in the porous parts of the granules is entrained in the water, thereby preventing a decrease in the amount of dissolved oxygen in the water. In addition, the porosity ensures air and water permeability, and allows the formation of a sand hiding area for shellfish (e.g., clams).

In the present invention, the calcium silicate-containing granules may contain aggregate.
In this specification, the aggregate refers to a material that does not dissolve or disintegrate in waters where shellfish live.
As the aggregate, in the case of cement mortar, fine aggregate is used, and in the case of lightweight aerated concrete, unreacted silica stone derived from the raw materials is used.
The maximum particle size of the aggregate in the calcium silicate-containing granules is preferably 500 μm or less, more preferably 400 μm or less, even more preferably 300 μm or less, even more preferably 200 μm or less, and particularly preferably 100 μm or less, from the standpoint of increasing the amount of aggregate flowing out of the net members during shellfish cultivation and leaving as little aggregate as possible behind when the shellfish are recovered.
The maximum particle size of the aggregate in the calcium silicate-containing granular material can be determined by collecting the insoluble residue (aggregate) in the calcium silicate-containing granular material and measuring its particle size according to the method specified in "6. Method for determining insoluble residue by hydrochloric acid-sodium carbonate method" of "JIS R 5202:2015" (Methods for chemical analysis of cement). In this case, the particle size can be determined using a sieve or a laser type particle size distribution measuring device.

The pore volume ratio of the calcium silicate-containing granules is preferably 30 to 80 volume%, more preferably 40 to 76 volume%, even more preferably 50 to 73 volume%, and particularly preferably 60 to 70 volume%. A pore volume ratio of 30 volume% or more is preferable in terms of the ease of settling of floating shellfish larvae (settling on the bottom in the pores) and the inhibition of bottom sediment acidification (increase in the amount of dissolved oxygen in the water due to the supply of air from the pores). A pore volume ratio of 80 volume% or less is preferable in terms of the inhibition of easy collapse of the calcium silicate-containing granules.
In this specification, the pore volume ratio refers to the ratio of voids (pores) having a diameter of 3 nm to 371 μm to the total amount (100 volume %) of voids present in the granules that constitute the calcium silicate-containing granular material.
The pore volume ratio can be measured by mercury intrusion porosimetry.

In the present invention, the calcium silicate-containing granular material includes granules having a particle size larger than the mesh openings of the mesh member described below.
Of the total amount (100% by mass) of calcium silicate-containing granular material, the proportion of granules having a particle size larger than the mesh opening of the mesh member is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more.
When this ratio is 50 mass% or more, the amount of granules that will not flow out of the net members and will serve as a substrate (granular material) for the floating shellfish larvae to settle within the net members will be increased, and therefore the amount of young or adult shellfish (sometimes referred to as "adult shellfish, etc." in this specification) obtained through aquaculture per unit mass of calcium silicate-containing granules will be increased.

Of the total amount (100% by mass) of calcium silicate-containing granular material, the proportion of granules having a particle size exceeding four times the mesh opening of the mesh member is preferably 50% by mass or less, more preferably 40% by mass or more, even more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less.
If the ratio is 50 mass% or less, the amount of calcium silicate-containing granules remaining in the netting material when recovering adult shellfish, etc. grown in aquaculture will be smaller, thereby reducing or eliminating the labor involved in separating the adult shellfish, etc. from the calcium silicate-containing granules.

In the present invention, the 50% mass cumulative particle size of the calcium silicate-containing granules (the particle size at which the granules reach 50% by mass of the total amount when accumulating from the minimum particle size to the maximum particle size) is preferably 0.3 to 5 mm, more preferably 0.6 to 4 mm, even more preferably 0.9 to 3.5 mm, even more preferably 1.2 to 3.0 mm, and particularly preferably 1.5 to 2.5 mm.
When the 50% cumulative particle size by mass is 0.3 mm or more, the amount of floating shellfish larvae that settle on the calcium silicate-containing granules can be increased.When the 50% cumulative particle size by mass is 5 mm or less, the amount of calcium silicate-containing granules remaining in the net member when recovering the adult shellfish grown in aquaculture is reduced.

In the present invention, the particle size distribution of the calcium silicate-containing granules is preferably such that the proportion of granules having a particle size of less than 0.5 mm is 20% by mass or less and the proportion of granules having a particle size exceeding 4 mm is 10% by mass or less, more preferably such that the proportion of granules having a particle size of less than 0.5 mm is 10% by mass or less and the proportion of granules having a particle size exceeding 4 mm is 5% by mass or less, and particularly preferably such that the proportion of granules having a particle size of less than 0.5 mm is 5% by mass or less and the proportion of granules having a particle size exceeding 4 mm is 2% by mass or less.
When the ratio of granules having a particle size of less than 0.5 mm is 20% by mass or less, the amount of floating shellfish larvae that settle on the calcium silicate-containing granules can be increased.When the ratio of granules having a particle size of more than 4 mm is 10% by mass or less, the amount of calcium silicate-containing granules remaining in the net member when recovering the adult shellfish grown in aquaculture is reduced.
In this specification, the particle size of the calcium silicate-containing granules corresponds to the mesh size of the mesh member described below. For example, if the particle size of the calcium silicate-containing granules is 1.0 mm, granules having a particle size exceeding 1.0 mm cannot pass through a mesh member having a mesh size of 1.0 mm.

The net member used in the present invention may be any material having sufficient durability and water resistance to be usable for a long period of time in water such as seawater.
An example of the net member is a bag-shaped member formed from a sheet-like material made by combining a plurality of fibrous bodies made of materials such as synthetic resin fibers and vegetable fibers in a lattice pattern.
Another example of a mesh member is one in which a mesh sheet is produced using an extrusion molding machine from a thermoplastic synthetic resin as the raw material, and then this sheet is formed into a basket shape (for example, a cylindrical shape with one end closed and the other end open).
The shape of the net member is bag-like or basket-like, and among these, a bag-like net member is preferably used in the present invention in terms of ease of storage when not in use and ease of carrying.
The shape of the mesh member (in the case of a bag shape, the shape when the entire member is unfolded) may be any shape that is openable only at the top, such as a rectangular prism with only the top surface open, or a cylinder with only the top surface open.
The net member may be a commercially available fish and shellfish farming material, such as an oyster farming basket manufactured by SEAPA Japan.

The mesh size of the mesh member is preferably 0.1 to 3 mm, more preferably 0.3 to 2.5 mm, even more preferably 0.4 to 2.0 mm, still more preferably 0.5 to 1.5 mm, and particularly preferably 0.7 to 1.3 mm.
If the mesh size is 0.1 mm or more, the amount of calcium silicate-containing granules remaining in the net member when recovering the cultured adult shellfish, etc. If the mesh size is 3 mm or less, the amount of calcium silicate-containing granules flowing out of the net member before the shellfish larvae settle on the bottom will be smaller.

Next, the shellfish farming method of the present invention will be described.
The shellfish farming method of the present invention includes an installation step of installing a shellfish farming system (comprising bag- or basket-shaped netting members containing calcium silicate-containing granular material) in an area of water where shellfish live, and a recovery step of recovering juvenile or adult shellfish from the shellfish farming system when shellfish larvae settle on the calcium silicate-containing granular material and then grow into juvenile or adult shellfish that are larger than the mesh openings of the bag- or basket-shaped netting members.
Each step will be described below.

[Installation process]
The installation step is a step of installing a shellfish farming system (comprising bag- or cage-shaped net members containing calcium silicate-containing granules) in a water area where shellfish live.
"Waters inhabited by shellfish" refers to marine, brackish or freshwater areas where the planktonic larvae of shellfish live.
Examples of water bodies where shellfish live include seas, lakes, swamps, and tidal flats.
The waters in which shellfish live may be places where the bottom sediment is not exposed (e.g., oceans or lakes with a suitable depth) or places where the bottom sediment is exposed (e.g., tidal flats that have no depth at low tide).

When the shellfish farming system is installed in a location where the bottom sediment is not exposed, the shellfish farming system can take a form in which the openings of the net members are fixed in a closed state using a fixing means such as string to a surface floating body such as a buoy or an oyster farming raft and the system is suspended in the water, or in which the openings of the net members are fixed in a closed state using a fixing means such as string to a sinker fixed to the bottom of the water and the system is suspended in the water above the sinker.
When the shellfish culture system is installed in a place where the bottom sediment is exposed, the shellfish culture system can be placed on the top surface of the bottom sediment with the openings of the net members closed, or partially buried in the bottom sediment with the openings of the net members closed, etc. In this case, it is desirable to fix the shellfish culture system to the bottom sediment using fixing means such as pegs so that it will not be washed away offshore, etc.
The timing of installation of the shellfish farming system is not particularly limited, but is preferably the time when the shellfish's floating larvae settle to the bottom or just before that (for example, in the case of the short-necked clam, April to August or October to February).
If the calcium silicate-containing granules are lost excessively due to leaching or wear and tear caused by rough weather prior to the subsequent recovery process, making it necessary to replenish them, new calcium silicate-containing granules may be replenished.

After the shellfish farming system is installed, the silicic acid leached from the calcium silicate-containing granules can promote the growth of algae such as diatoms (e.g., diatoms that attach to the bottom sediment and diatoms that float in the water) that serve as food for shellfish.
In addition, calcium eluted from the calcium silicate-containing granules can promote the growth of shellfish (particularly shell formation).
Furthermore, the calcium silicate-containing granules make the surrounding pH alkaline, suppressing the acidification of the bottom sediment that accompanies the decomposition of organic matter in the bottom sediment, and also reducing the activity of sulfate-reducing bacteria that cause the generation of hydrogen sulfide. As a result, the mortality of shellfish is suppressed, and an increase in the amount of shellfish recovered in the subsequent recovery process can be expected. Furthermore, the shellfish recovered can be expected to be healthy (highly commercial) with no abnormalities such as blackening of shells due to hydrogen sulfide.

[Recovery process]
The recovery process is a process in which shellfish larvae settle on the calcium silicate-containing granules of a shellfish cultivation system installed in a water area, and then when they grow into young or adult shellfish that are larger than the mesh openings of the bag-shaped or basket-shaped netting members, the young or adult shellfish are recovered from the shellfish cultivation system.
For example, in the case of harvesting baby clams, the baby clams may be harvested when they have grown to about 10 to 15 mm in size. The baby clams may then be cultured in other waters until they become adults.
When collecting adult clams, collection work can be carried out when the clams have grown to an appropriate size of 15 mm or more (for example, 20 mm or more about one year after installation, or 30 to 40 mm after about two years, which is considered the ripe size for eating).
By the time the adult shellfish are harvested, the calcium silicate-containing granules in the shellfish farming system have become smaller in particle size due to dissolution and disintegration. Therefore, by sieving the bag- or basket-shaped netting members before harvesting the shellfish, the calcium silicate-containing granules can be removed together with the bottom sediment that has become mixed in the netting members, allowing the shellfish to be easily harvested in a short time.

In the present invention, another net member may be arranged outside the net member constituting the shellfish farming system of the present invention in a manner that accommodates the net member.
In this case, the other net members can be ones (bag-shaped or basket-shaped) that have the same configuration as the net members that make up the shellfish farming system of the present invention, except that they have smaller mesh openings than the net members that make up the shellfish farming system of the present invention.
By using another mesh member, a portion of the calcium silicate-containing granules can be recovered and reused.
In this case, the material that passes through the net member constituting the shellfish culture system of the present invention and the other net members is, for example, unreacted silica stone derived from the raw material contained in the calcium silicate-containing granular material. The unreacted silica stone derived from the raw material usually has a particle size of about 10 to 100 μm. Therefore, if the net member constituting the shellfish culture system of the present invention has a mesh size within the above-mentioned preferred range (for example, 1.0 mm), and the other net members have a mesh size less than the lower limit (for example, 0.3 mm, 0.4 mm, etc.) of the above-mentioned "more preferred range" of the mesh size of the net member of the present invention (for example, 0.2 mm), the aggregate remaining after the dissolution or disintegration of the calcium silicate-containing granular material passes through the net member of the present invention and the other net members on the outside thereof, so that only the calcium silicate-containing granular material having the desired particle size (for example, 0.2 to 1.0 mm) can be recovered from the other net members.

In the present invention, the contents (shellfish and small amounts of other contents such as bottom sediment and calcium silicate-containing granular material) are removed from the net members constituting the shellfish farming system of the present invention, and the removed contents are then sieved using a sieve with mesh openings that match the size of the shellfish to be recovered (e.g., 30 mm or more in the case of clams), with washing if necessary, to recover only the shellfish.
Even in this case, the amount of calcium silicate-containing granules is less than when the shellfish farming system was first installed, so the sieving process can be completed easily and in a short time.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
[Experimental Example 1]
An experiment was conducted to determine whether or not clam larvae would settle to the bottom when using the shellfish farming system of the present invention.
(1) Materials used (a) Calcium silicate-containing granular material: crushed lightweight aerated concrete (main component: tobermorite; pore volume ratio: 65% by volume; acid-insoluble residue: 35.5% by mass; particle size of unreacted silica derived from raw materials: completely passes through a sieve with 100 μm openings)
The particle size distribution of the calcium silicate-containing granules is as shown in Table 1.
In Table 1, "<0.5 mm" indicates a particle size of 0.5 mm or less, "0.5-1 mm" indicates a particle size of more than 0.5 mm and less than 1.0 mm, "1-2 mm" indicates a particle size of more than 1.0 mm and less than 2.0 mm, "2-3 mm" indicates a particle size of more than 2.0 mm and less than 3.0 mm, "3-4 mm" indicates a particle size of more than 3.0 mm and less than 4.0 mm, and ">4 mm" indicates a particle size of more than 4.0 mm. "<", "~", and ">" in Tables 2 and 4 also have the same meaning as in Table 1, from smaller values to larger values.

(b) Bag-shaped net member: vegetable harvesting net (shape: bag-shaped; material: synthetic resin fiber; dimensions: 42 cm x 70 cm; capacity: 23 liters; mesh size: 1.0 mm)
(2) Experimental Method A shellfish farming system of the present invention was prepared by placing 5 kg of calcium silicate-containing granular material in a bag-shaped net member. A total of six similar sets were prepared, and these were named "No. 1" to "No. 6."
The shellfish farming systems (No. 1 to No. 6) were fixed to the bottom sediment of the tidal flats with pegs, and after nine months, (i) the number and size of shellfish (clams, oysters) that had settled inside the bag-shaped netting members, (ii) the environment of the settlement location (inside the calcium silicate-containing granules and the bottom sediment below the bag-shaped netting members), and (iii) the change over time in the particle size distribution of the calcium silicate-containing granules were evaluated.
The evaluation items for the environment of the bottom landing site in (ii) above were pH (a measure of the presence or absence of acidification) and redox potential (a measure of the presence or absence of hypoxia).
The experimental period was nine months, from June to March of the following year.
The results are shown in Tables 2 to 4.

From Table 2, we can see that within nine months of the installation of the shellfish farming system, an average of approximately 177 juvenile and adult clams with body lengths ranging from 9.5 to 22.4 mm grew per set.
It can also be seen that the oysters grew, on average, about 39 per set.
Table 3 shows the average values of measurements taken nine months after installation in each of the shellfish culture systems (No. 1 to No. 6).
From Table 3, it can be seen that with the shellfish farming system of the present invention, the pH is within a range that is good for shellfish growth (similar to a pH of seawater), and the oxidation-reduction potential is within a range that is good for shellfish growth (not in an oxygen-depleted state).

Table 4 shows the average values of the particle size distribution of calcium silicate-containing granules measured at each time point, 5 months and 9 months after installation in each of the shellfish farming systems (No. 1 to No. 6).
From Table 4, it can be seen that the particle size of the calcium silicate-containing granules decreases over time.
In Table 4, the reason why the proportion of particles with a particle size of over 4 mm increases from "0.0% by mass""beforeinstallation" to "0.2% by mass""after 5 months" is because the locations where the particle samples were taken "before installation" and "after 5 months" are slightly different. The same reason is also why data showing an increase in the proportion of particles with large particle sizes over time is seen.

[Experimental Example 2]
An experiment (Example) was conducted to determine whether or not the short-necked clam would grow well if it was cultured for a long period of time using the shellfish culture system of the present invention. In addition, as a control experiment (Comparative Example), the experiment was conducted in the same manner as in the Example, except that gravel chips were used instead of the calcium silicate-containing granules used in the present invention.
(1) Materials used (a) Calcium silicate-containing granules: the same as in Experimental Example 1 (granules of the example)
(b) Gravel chips (for comparison): Grain size of 10 to 15 mm (comparative granular material)
(c) Bag-shaped net member: Same as in Experimental Example 1

(2) Experimental Method 5 kg of calcium silicate-containing granules were placed in a bag-shaped net member to prepare a shellfish farming system of the present invention.
The shellfish farming system was fixed to the bottom of the tidal flat with pegs, and the number of surviving and dead clams (dead shells) was counted at each time point after 11 and 16 months. The survival rate (%) of the clams was calculated from these numbers. In addition, the presence or absence of hydrogen sulfide odor from the granular material (calcium silicate-containing granular material or gravel chips), which is an indicator of the degree of deterioration of the bottom sediment environment, was examined.
In the experiment (Example) using calcium silicate-containing granules, the mass of each individual clam and the mass of the shucked meat were measured, and the fatness index was calculated.
The experimental period was 16 months, from June to October of the following year.
The results are shown in Tables 5 and 6.

From Tables 5 and 6, it can be seen that when calcium silicate-containing granules (Example; granules of the present invention) were used, the environment was better (no hydrogen sulfide odor), the survival rate of the clams was higher (approximately 84% at 16 months), and the growth conditions were also better (Table 6) than when gravel chips (Comparative Example; control granules) were used.

Claims (6)

A shellfish farming system comprising a bag-shaped or basket-shaped net member and calcium silicate-containing granules contained in the net member,
A shellfish farming system characterized in that the calcium silicate-containing granules include granules having a particle size larger than the mesh openings of the net member. The shellfish farming system according to claim 1, wherein the mesh size of the netting members is 0.1 to 3 mm. The shellfish farming system according to claim 1 or 2, wherein the calcium silicate-containing granular material contains granules having a particle size larger than the mesh opening of the net member at a ratio of 50% by mass or more, and does not contain granules having a particle size more than four times the mesh opening of the net member or contains granules at a ratio of 50% by mass or less. The shellfish farming system according to any one of claims 1 to 3, wherein the calcium silicate-containing granules are made of a porous material containing at least one selected from the group consisting of tobermorite, xonotlite, CSH gel, foshagite, gyrolite, hillebrandite, and wollastonite. The shellfish farming system according to any one of claims 1 to 4, wherein the calcium silicate-containing granules include aggregates having a maximum particle size of 500 μm or less. A shellfish farming method using the shellfish farming system according to any one of claims 1 to 5,
An installation step of installing the shellfish farming system in a water area where shellfish live;
a recovery step of recovering the juvenile or adult shellfish from the shellfish culture system when the shellfish larvae settle on the calcium silicate-containing granules and then grow into juvenile or adult shellfish that are larger than the mesh openings of the netting member;
A shellfish farming method comprising: