JP2020178616A - Culture method of short-neck clam - Google Patents

Abstract

To provide an efficient and inexpensive culture method of short-neck clams.SOLUTION: A culture method of short-neck clam includes step (A) for filtering short-neck clams by using a net filter with a mesh size of 0.6 mm or less, to thereby recover young shells thereof, and step (b) for putting young shells of short-neck clams into a net with the mesh size of 0.6 mm or less, and discharging them into the sea. In the culture method of short-neck clam, an average shell length of young shells of short-neck clams after being filtered by using the net filter used in the step (A) is 1.0 mm or less.SELECTED DRAWING: Figure 4

Description

The present invention relates to a method and an apparatus for efficiently and inexpensively culturing clams.

The catch of domestic clams nationwide peaked at 160,000 tons per year in 1983 and has been steadily declining. In 2016, it reached 8,500 tons per year, setting a new record low.

The factors behind this decrease in the catch of clams are the loss of clam habitat due to coastal construction including reclamation and reclamation, river improvement, water pollution, etc., and the occurrence of sediment mud, oxygen depletion, and red tide. Deterioration of the environment has been pointed out.

On the other hand, the annual consumption of domestic clams is 60,000 to 100,000 tons, so the shortage of domestic products depends on the import of foreign clams from China and South Korea. At present, as a result of such an increase in the import volume of foreign-produced clams, the ratio of domestic clams to the total consumption of clams has dropped to less than 20%.

In view of this situation, various efforts are being made by national and prefectural research institutes to restore clam resources. One of them is a method of cultivating clams.

However, the current amount of clams cultivated is about 100 tons per year, and the catch of domestically produced clams has not been raised.

Clam farming itself is not particularly difficult if it costs money and manpower, such as culturing in a water tank on land until the end. However, since the wholesale price of clams is not expensive at 600 to 700 yen per kilogram, there is a problem that it is not profitable if cost and labor are spent.

In particular, when the shell length of juvenile clams exceeds 0.5 mm, the amount of food to be eaten increases, and the cost of food such as plankton is a factor that pushes up the price of cultured clams.

In the conventional cultivation of clams, the clams are cultivated in a water tank on land until the shell length of the clams reaches a size of 10 mm (1 cm), and then they are placed in a mesh net of a size that the clams do not pass through. The method was to release it into aquaculture areas where food is abundant.

Clam larvae are cultivated in aquaculture tanks on land until they reach a size of 10 mm (1 cm). If they are released into the cultivated sea area at the stage of smaller larvae, they are exposed to the external environment without strong vitality. Therefore, it was believed that the rate of death would increase due to predation by other fish, illness, and inability to adapt to the environment.

Examples of currently known methods for culturing clams include the following Patent Documents 1 to 3.

Japanese Unexamined Patent Publication No. 2008-92901 Japanese Unexamined Patent Publication No. 2012-239400 JP-A-2017-158496

However, although it is possible to cultivate clams by either method, there are problems in terms of cost and labor, and the catch is not significantly increased.

As a result of diligent research, the present inventors have found that even if the clam larvae are released into the sea area when the shell length is about 0.7 mm or less, they can be sufficiently cultivated depending on the environment.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method and an apparatus for culturing clams efficiently and inexpensively.

As a means for achieving the above object, the clam farming method according to claim 1 selects young clams of a certain size or larger by filtering using a net filter having a mesh size of 0.6 mm or less. It is characterized by including a step (A) of collecting the collected clams and a step (B) of putting the collected young clams in a net having a mesh size of 0.6 mm or less and discharging them into the sea.

Next, the method for culturing clams according to claim 2 is characterized in that the mesh size of the net filter used in the step (A) is 0.5 mm or less.

Next, the method for culturing clams according to claim 3 is characterized in that the average shell length of the young clams after filtering using the net filter used in the step (A) is 1.0 mm or less. To do.

Next, the method for culturing clams according to claim 4 is characterized in that the mesh size of the net used in the step (B) is 0.5 mm or less.

Next, the method for culturing clams according to claim 5 is further characterized by including a step of breeding young clams with a downwelling breeding device.

In the method for cultivating clams according to the present invention, by releasing the juvenile clams into the aquaculture area where the feed is abundant at a relatively early stage, it is possible to save the labor of feed and breeding, and the clams are cultivated efficiently and inexpensively. can do.

It is a perspective view which shows the structure of the juvenile mussel container 1. It is sectional drawing which shows the structure of the downwelling breeding apparatus. It is a perspective view which shows the structure of the iron frame 40. It is the figure below the sea surface which shows the outline of the hanging type aquaculture.

(Selection of parent shell)
The spawning season of short-necked clams in western Japan is approximately twice a year from April to June and October to November, or once a year from July to August (it may change depending on the feeding environment in the sea area, etc.). Obtain mature clams.

Whether it is a mature parent or not is determined by opening some of the collected parent shells and piercing the gonads, which look like milky white bags, with needles to see if the white liquid seeps out. Determine. If 70 to 80% of the observed individuals are in such a situation, it can be said that it is a suitable time for egg collection work.

The size of the individual clam is preferably about 3 to 4 cm.

(Induction of spawning)
It induces spawning by giving an external stimulus to the mature parent mussel. That is, after washing the parent mussels thoroughly with tap water, they are dried in the shade for about 1 hour and then immersed in cold seawater and warm seawater repeatedly.

As cold seawater, prepare seawater at 15 ° C. If the temperature of seawater is 15 ° C or higher, cool it with ice and prepare it. Seawater is preferably microfiltered or sterilized so that organisms other than clams do not get mixed in. However, it is also possible to use the seawater as it is.

Use an air pump and air stone to provide weak ventilation so that the seawater in the aquarium slowly convects.

After about 500 g of the parent mussel is stored in cold seawater for about 15 to 30 minutes, the water temperature is raised to 25 ° C. using an electric heater to stimulate the temperature rise. At this time, if the parent mussel is sufficiently matured, spawning and fertilization will start at this stage.

If spawning / fertilization does not start even after reaching 25 ° C for 1 hour, move the parent shell to a water tank filled with cold seawater again, give a cooling stimulus for about 30 minutes, and then again. Raise the water temperature to 25 ° C. At this time, a few drops of white liquid taken out by incising the gonads by collecting several individuals of the parent shell are added to the aquarium. This triggers the ejaculation of clams in the aquarium.

When spawning / fertilization begins, a white liquid like smoke is released from the water pipe of the clam, and the water in the aquarium becomes pure white. Move the parent shell to another new aquarium within 60 minutes of spawning / fertilization. This is to prevent the fertilized egg from being sucked into the clam.

Spawning of parent mussels is completed in about 2 to 4 hours. During this time, the parent shell is repeatedly moved to another new aquarium. It should be noted that it is not necessary to adjust the temperature of the seawater when preparing a new aquarium because the parent mussels that have started spawning are not stopped in the middle.

(Egg collection)
Fertilized eggs are collected using an egg collection net. Since the size of the fertilized egg is about 60 μm, a net for egg collection having a mesh size of 25 μm is used, for example. Since the size of sperm is about 2 μm, it passes through an egg collection net. The sperm that are no longer needed in this way are separated from the fertilized egg.

In addition to the necessary fertilized eggs, the seawater after spawning and fertilization contains fine dust and feces of parent shells, so for example, a dust collecting net with a mesh size of 90 μm is placed in front of the spawning net. Install in and remove these. Since the size of the fertilized egg is smaller than the mesh size of the dust collecting net, it can pass through the dust collecting net.

The actual egg collection work is performed by taking out the parent shell from the seawater after spawning and fertilizing, and then pouring it with a hose or the like into the place where the dust collecting net is superposed on the spawning net.

The collected fertilized eggs are thoroughly washed with microfiltration or sterilized seawater to remove excess sperm and the like.

After washing, fertilized eggs are transferred to a bucket and about 10 liters of seawater is added. After stirring this well, take 0.2 mL to 1 mL with a pipette and count the number of fertilized eggs in it with a microscope to calculate the approximate number of fertilized eggs in the bucket by proportional calculation.

Once the number of fertilized eggs obtained is known, transfer to a hatching aquarium. The upper limit of the accommodation density of the hatching tank is 3,000 to 4,000 grains per 1 cm ² of the bottom area. For example, when a 200 L FRP square water tank is used, the bottom area is about 5,000 cm ² , so that about 20 million fertilized eggs can be accommodated.

Clam eggs are almost subsided until hatching. A flat-bottomed aquarium is used as the hatching aquarium so that fertilized eggs do not gather in one place and overlap. The water temperature is set to around 23 ° C, and weak ventilation is performed with an air pump and air stone. If the temperature is 20 ° C or higher and the water tank is not heated, ventilation is not necessary.

(Recovery of larvae)
The fertilized egg hatches 5 to 6 hours after fertilization and becomes a veliger larva (also called a D-type larva because of its shape similar to the letter "D". Hereinafter referred to as "D-type larva") in about 24 hours. Since this D-type larva has a larva and is resistant to physical impact, it is recovered from the hatching tank after waiting for this stage.

Since the size of the D-type larva in this stage is about 100 μm, for example, the mesh for collecting the net can be 40 μm and the mesh for collecting dust can be 125 μm.

After collecting the D-type larvae, measure the number of larvae with a microscope. Unlike the case of fertilized eggs, D-type larvae swim and cannot be measured as they are. Formalin and ethanol are dropped into 20 to 30 mL of seawater by about 1 drop each to stop the movement before measurement.

(Larva breeding)
D-type larvae are housed in a breeding aquarium at a storage density of 3-5 individuals / mL. For the breeding aquarium, breeding water prepared by adding 10% of tap water to seawater, sterilized filtered seawater, and the like are used. Keep the breeding water temperature around 23 ° C and ventilate the water in the aquarium to the extent that it slowly convects. If the water temperature is below 20 ° C, the growth will be slow, and if it exceeds 30 ° C, the survival will be poor.

Plankton is used as bait. For example, Isocrisis Tahitian strain, Quitocellos calcitrans, Quitocellos neograsile and the like can be used as appropriate according to the growth of D-type larvae. The feeding amount is initially given at 20,000 cells / mL, and then gradually increased according to the survival number and growth of D-type larvae, and the amount of 40,000 cells / mL is given once a day.

Around the 5th day after hatching, breeding water is made from seawater that has been sterilized and filtered, and the water is transferred after adjusting the water temperature.

Basically, daily management is only feeding. However, check the density of D-type larvae with a pipette every day, and if dust accumulates, clean it.

About two weeks after breeding, individuals with shell lengths exceeding 200 μm begin to appear, and an ax foot is created to shift from the floating life to the benthic life. When most individuals have an ax foot, they are collected from the larval breeding aquarium using a net with a mesh size of 100-125 μm.

(Frying shellfish 1)
In the first period when the juveniles are small, they are bred in an aquarium. Breeding water is made at a ratio of seawater 2: tap water 3 and the collected juveniles are stored. The breeding temperature should be kept at 20 ° C or higher as necessary, and the water in the aquarium should be ventilated weakly to the extent that it slowly convects.

If necessary, spray powdered shell fossils on the bottom of the aquarium. The amount of spraying may be small, and in the case of a 500L aquarium, the amount of fossil shellfish sprayed may be about 50 to 100 g, and the bottom of the aquarium may be slightly whitened.

The accommodation density in juvenile mussels is about 20 to 50 individuals per 1 cm ^{2 of} bottom area.

The bait may be Isocrisis Tahiti strain or Quitocellos calcitrans, but Quitocellos neograsile (trade name: Gracilis) having larger cells is preferable. When 300,000 individuals are housed in a 500 L aquarium, the amount of feed is about 50 to 100 mL per day at the start of breeding of juvenile mussels.

Daily management is only feeding, not bottom cleaning. Since the bottoming of the juveniles is completed in 1 to 2 weeks, at this stage, the juveniles are collected from the juvenile breeding aquarium using a net with a mesh size of 27 μm.

(Frying shellfish 2)
When it is time for the juveniles to settle, they are then housed in the downwelling breeding device 4 for breeding. The breeding temperature is heated as necessary so as to maintain 20 ° C. or higher.

<Downwelling breeding device>
The outline and manufacturing method of the downwelling breeding apparatus 4 will be described below. However, the downwelling breeding apparatus 4 is not limited to the one described below, and can be appropriately devised or designed.

First, a method of manufacturing the juvenile mussel container 1 will be described with reference to FIG. Prepare a PVC pipe 2 having a diameter of 30 to 60 cm cut into round slices to a depth of about 20 to 30 cm. A 0.15 mm mesh net 3 is attached to the inside of the net 3 with an instant adhesive or the like.

Next, a method of manufacturing the downwelling breeding apparatus 4 will be described with reference to FIG. A water tank 5 is prepared, and breeding water 6 is prepared at a ratio of seawater 2: tap water 3 and injected into the water tank 5. The support plate 7 is fixed in the water tank 5 in a floating state, and the juvenile mussel container 1 is installed on the support plate 7. When culturing in large quantities, a plurality of juvenile mussels may be installed.

In order to continuously inject seawater containing feed from above the juvenile mussel container 1, the feeding device 10 is injected into the water tank 5.
To install. The feeding device 10 includes a feeding pipe having a pump 12 and a feeding hole 11. When the feeding device 10 is operated, the breeding water 6 containing the feed is sucked up by the pump 12 in the direction of the arrow 30, advances through the feeding pipe in the direction of the arrow 31, and is discharged from the feeding hole 11 to the juvenile mussel container 1. It is injected in the form of dropping onto the top. The breeding water 6 containing the feed descends the juvenile mussel container 1 in the direction of arrow 32, passes through the support plate 7 and proceeds in the direction of arrow 33, and returns to the pump 12 again.

When the breeding water 6 containing the feed advances through the juvenile mussel container 1 in the direction of the arrow 32, it passes by the juvenile mussels that have settled on the mesh net 3. In this way, a situation is created in which the feed is constantly flowing around the juveniles, and the juveniles can efficiently prey on the feed.

As described above, the downwelling breeding apparatus 4 is used to breed the juvenile mussels until the shell length exceeds 0.7 mm.

In the above, the juvenile mussels have been bred starting from the spawning of the parent mussels, but instead of going through this step, the following may be applied after purchasing the juvenile mussels of the same size from others.

(Intermediate training)
When the proportion of individuals with a shell length exceeding 0.7 mm increases, the juvenile clams are taken out from the juvenile clam container 1 and injected into a net having a mesh size of 0.6 mm or less, for example, a net having a mesh size of 0.5 mm. Collect the clams. The clams that are not collected by this net are returned to the downwelling breeding device 4 and kept until they grow large.

The average shell length of the juvenile clams recovered at this stage is preferably 1.0 mm or less, more preferably 0.8 mm or less. The average shell length can be measured by observing about 10 to 100 juvenile clams with a microscope.

The collected clams are transferred to a bag 70 made of a net having a mesh size of 0.5 mm. An iron frame 40 as shown in FIG. 3 is placed in the bag 70 in advance. The size and shape of the iron frame 40 are not particularly limited, but for example, a rectangular parallelepiped having a length and width of 40 cm and a height of 20 cm is adopted. The purpose of putting the iron frame 40 in the bag 70 is to secure a space inside the bag and to submerge the entire bag in the sea. FIG. 4 is a diagram showing a state in which the bag 70 containing the iron frame 40 is placed in the sea.

Then, a raft is installed near the coast where food such as plankton is abundant as much as possible, and the bag containing the juvenile clams prepared as described above is hung at a depth of 2 to 3 m from the sea surface.

If the area is nutritious, the juveniles will grow to about 1.5 mm in a few weeks. After confirming that the juveniles have grown to about 1.5 mm, they are then transferred to a net with a mesh size of 1 mm, and the iron frame 40 is inserted in the same manner and put into the sea again in the same manner.

In about two months after that, the juveniles grow to about 7 to 8 mm.

(Covered net aquaculture / hanging aquaculture)
After the difference grows to this extent, it is bred to the final stage by cover net aquaculture or hanging aquaculture. Cover net aquaculture is a culture method in which the tidal flat surface is sprayed and the cover net protects it from feeding damage and runoff.

The hanging-type aquaculture is a aquaculture method in which a substrate such as sand or anthracite is stored in a basket or container from a raft and hung at a depth of 2 to 3 m from the sea surface. In order to protect the clams from foreign enemies, it is desirable to cover the basket or container with a net with a mesh size of about 20 mm.

After about 6 to 10 months in this state, the clams grow to a product size of 3.5 to 4 cm.

1 juvenile clam cage 2 PVC pipe 3 0.15 mm mesh net 4 Downwelling breeding device 5 Water tank 6 Breeding water 7 Support plate 10 Feeding pipe 11 Feeding hole 12 Pump 40 Iron frame 50 Sea 60 Rope 70 bag

Claims (5)

The step (A) of selecting and collecting the young clams of a certain size or larger by filtering using a net filter with a mesh size of 0.6 mm or less, and the collected young clams of 0.6 mm. A method for cultivating clams, which comprises a step (B) of putting the clams in a net having the following meshes and releasing them into the sea. The method for culturing clams according to claim 1, wherein the mesh size of the net filter used in the step (A) is 0.5 mm or less. The cultivation of clams according to claim 1 or 2, wherein the average shell length of the young clams after filtration using the net filter used in the step (A) is 1.0 mm or less. Method. The method for culturing clams according to any one of claims 1 to 3, wherein the mesh size of the net used in the step (B) is 0.5 mm or less. The method for cultivating clams according to any one of claims 1 to 4, further comprising a step of breeding young clams in a downwelling breeding device.