Edible fish production method and edible fish

Abstract

By mitigating a stress load that is due to a decrease in water quality, tolerance of an osmotic pressure stress load is increased, a flavor enhancement effect is increased, and death risk is decreased, and thus edible fish with higher umami compared to before are efficiently produced without causing death in said edible fish. This edible fish production method includes: a first step in which the supply of feed to edible fish that are reared in first rearing water is halted; a second step in which, after the supply of feed to the edible fish has been halted, the rearing water for the edible fish is transitioned from the first rearing water to a second rearing water that has a higher salinity than the salinity of the first rearing water; and a third step in which, after the rearing water for the edible fish has been transitioned from the first rearing water to the second rearing water, the edible fish are landed from the second rearing water.

Description

[Technical field]

[0001] The present invention relates to a method for producing edible fish and to edible fish. [Background technology]

[0002] The following Patent Document 1 describes a method for cultivating rainbow trout and coho salmon in freshwater and seawater and shipping them.

[0003] The following Patent Document 2 describes an invention in which yellowtail, red sea bream, goldfish, prawns, and clams are immersed in an aqueous solution containing various amino acids, including alanine and valine, to increase the amino acid concentration in the muscles.

[0004] Furthermore, a "flavor-enhancing" technique that utilizes the osmoregulatory mechanism of fish is already known, as seen in the following Non-Patent Document 1. "Flavor-enhancing" is a technique that improves flavor by exposing farmed fish immediately before shipping to high-salinity water to temporarily increase the amino acid content in the fish meat.

[0005] The following Non-Patent Document 1 describes an invention in which tiger pufferfish are transferred from an environment with a salinity of 0.9% to seawater with a salinity of 3.5%, thereby increasing the levels of various amino acids in the muscles. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6626608 [Patent Document 2] JP 2019-187304 A [Non-patent literature]

[0007] [Non-Patent Document 1] Katsuaki Noguchi, "Development of a closed circulation type tiger pufferfish farming system using hot spring water", Journal of the Japanese Society of Fisheries Science, Japan Fisheries Society, 2017, Vol. 83, No. 5, pp. 750-753 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to increase resistance to osmotic stress by alleviating stress caused by deterioration of water quality, thereby maximizing the flavor-enhancing effect and reducing the risk of mortality, thereby efficiently producing edible fish with high umami taste compared to conventional methods without mortality. [Means for solving the problem]

[0009] A first aspect is a method for producing edible fish, comprising: a first step of stopping the supply of feed to edible fish raised in a first rearing water; a second step of transferring the rearing water of the edible fish from the first rearing water to a second rearing water having a salinity higher than the salinity of the first rearing water after stopping the supply of feed to the edible fish; and a third step of transferring the rearing water of the edible fish from the first rearing water to the second rearing water, and landing the edible fish from the second rearing water.

[0010] A second embodiment is a method for producing food fish according to the first embodiment, wherein the fasting period during which feed supply is stopped prior to landing is a period not exceeding 4 days.

[0011] A third aspect is a method for producing edible fish according to the first or second aspect, wherein the high salinity treatment period during which the fish are reared in the second rearing water before landing does not exceed three days.

[0012] A fourth aspect is a method for producing edible fish in any of the first to third aspects, wherein the blood osmotic pressure of the edible fish increases by 20% or more relative to the blood osmotic pressure during rearing in the first rearing water within a period not exceeding two days after transfer from the first rearing water to the second rearing water.

[0013] A fifth aspect is a method for producing edible fish according to any one of the first to fourth aspects, wherein the alanine concentration in the muscle of the edible fish at the time of landing is increased to 1.5 times or more the alanine concentration in the muscle of the edible fish when transferred from the first rearing water to the second rearing water.

[0014] A sixth aspect is a method for producing edible fish according to any one of the first to fifth aspects, wherein the first rearing water is freshwater or rearing water with a low salinity concentration having an osmotic pressure of 250 mOsm / kg or less.

[0015] A seventh aspect is the method for producing edible fish according to the sixth aspect, wherein the edible fish is a fish species capable of growing in freshwater and seawater.

[0016] An eighth aspect is the method for producing edible fish according to the seventh aspect, wherein the edible fish is a species belonging to the Salmonidae family.

[0017] A ninth aspect is the method for producing edible fish according to the eighth aspect, wherein the edible fish is rainbow trout.

[0018] A tenth aspect is a method for producing edible fish according to any of the sixth to ninth aspects, wherein the second rearing water is rearing water with a high salinity, that is, a salinity of 27‰ or more or an osmotic pressure of 800mOsm / kg or more.

[0019] An eleventh aspect is a method for producing edible fish according to any one of the first to fifth aspects, wherein the edible fish are a species of fish that cannot grow in seawater.

[0020] A twelfth aspect is a method for producing edible fish according to the eleventh aspect, wherein the second rearing water is rearing water with a high salinity having a salinity of not exceeding 14‰ or an osmotic pressure of not exceeding 400 mOsm / kg.

[0021] A thirteenth aspect is a method for producing edible fish, including rainbow trout, in any one of the first to tenth aspects, having a blood osmotic pressure of 382 mOsm / kg or more.

[0022] A fourteenth aspect is a method for producing edible fish, comprising the steps of producing edible fish, including rainbow trout, having an alanine concentration in muscle of 7.1 mM or more in any one of the first to tenth and thirteenth aspects.

[0023] A fifteenth aspect is an edible fish including rainbow trout that has been landed after a fasting period and has a blood osmotic pressure of 382 mOsm / kg or more.

[0024] A sixteenth aspect is an edible fish, including rainbow trout, that has been landed after a fasting period and has an alanine concentration in muscle of 7.1 mM or more.

[0025] A seventeenth aspect is an edible fish, including rainbow trout, that has been caught after a fasting period and that exhibits a significant increase in the gene expression level of ALT (alanine aminotransferase), which is involved in alanine biosynthesis in muscle, compared to the same species of edible fish. Effect of the Invention

[0026] According to the present invention, the fish are exposed to high salinity water after fasting, which alleviates stress caused by deterioration of water quality and improves resistance to osmotic stress. This maximizes the flavor enhancement effect and reduces the risk of death, and enables efficient production of edible fish with high umami taste without death compared to conventional methods. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is a flow chart illustrating each step of the edible fish production method of the first and second embodiments. [Diagram 2] 2(A) and (B) are timing charts illustrating the edible fish production methods of the first and second embodiments, respectively. [Diagram 3] FIG. 3 is a graph showing the measurement results of the example, which is a graph showing the change in alanine concentration in the muscle of rainbow trout. [Figure 4]FIG. 4 is a graph showing the measurement results of the embodiment, which is a graph showing the change in glutamic acid concentration in the muscle of rainbow trout. [Diagram 5] FIG. 5 is a graph showing the measurement results of the example, which is a graph showing the change in anserine concentration in the muscle of rainbow trout. [Figure 6A] FIG. 6A is a graph showing the gene expression level of ALT, which is involved in alanine biosynthesis in muscle of edible fish produced by the edible fish production method of the first embodiment, in comparison with a comparative example. [Figure 6B] FIG. 6B is a graph showing the gene expression level of another species of ALT involved in alanine biosynthesis in muscle of edible fish produced by the edible fish production method of the first embodiment, in comparison with a comparative example. [Figure 7] FIG. 7 is a graph showing the plasma osmotic pressure of edible fish produced by the edible fish production method of the first embodiment in comparison with a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] BEST MODE FOR CARRYING OUT THE DISCLOSURE Hereinafter, a first embodiment of the edible fish production method and edible fish according to the present invention will be described with reference to the drawings.

[0029] (First embodiment)

[0030] FIG. 1 is a flow chart showing the steps of the edible fish production method of the first embodiment.

[0031] 2(A) and (B) are timing charts showing the edible fish production method of the first embodiment.

[0032] The edible fish targeted in the first embodiment is rainbow trout. Rainbow trout is a fish species belonging to the salmonidae family and can grow in both freshwater and seawater.

[0033] (1st step)

[0034] The first tank holds first breeding water, which may be fresh water, for example.

[0035] A predetermined number of rainbow trout are housed in the first tank. The rainbow trout are raised while being fed periodically. The first rearing water does not necessarily have to be freshwater, and may be rearing water with a low salinity that is different from the second rearing water. The first rearing water is desirably rearing water with a low salinity of 250 mOsm / kg or less.

[0036] A feeding cessation start date and time T1 is set at a specified date and time before the rainbow trout are landed, and the supply of food to the rainbow trout reared in the first rearing water is stopped during a specified fasting period (T1 to Te1) from the feeding cessation start date and time T1 to the fasting end date and time Te1.

[0037] By stopping the supply of food to the rainbow trout, deterioration of water quality such as an increase in ammonia concentration is suppressed, and the stress on the rainbow trout caused by deterioration of water quality is mitigated.

[0038] It is desirable that the fasting period (T1~Te1) should not exceed four days before landing the rainbow trout. If the fasting period (T1~Te1) is longer than four days, the free amino acid concentration in the rainbow trout's body will decrease, and the lipid content will decrease, which may result in a decrease in the quality of the fish as an edible fish.

[0039] The fasting end date and time Te1 may be the start T2, middle, or end Te2 of the high-salinity treatment period (T2 to Te2) described later. It is preferable that the fasting end date and time Te1 is a time when there is no significant deterioration in water quality due to excretion or spitting. The fasting end date and time Te1 may be a time when the risk of death can be reduced and the flavor-improving effect can be enhanced (first step S1).

[0040] (2nd process)

[0041] The rainbow trout are transferred from the first tank to the second tank at a second rearing water transfer date and time T2 that is later than the feeding stop start date and time T1 when the supply of food to the rainbow trout is stopped. The second tank stores second rearing water. The second rearing water is, for example, 80% diluted seawater. The 80% diluted seawater corresponds to rearing water with a high salinity of 27‰ or 800mOsm / kg osmotic pressure. The second rearing water is not necessarily limited to seawater diluted with tap water or distilled water, but may be any rearing water with a salinity higher than that of the first rearing water. The second rearing water is desirably rearing water with a high salinity of 27‰ or more or 800mOsm / kg or more osmotic pressure.

[0042] The transition from the first breeding water to the second breeding water does not necessarily have to involve a transition from the first tank to the second tank, and may involve replacing the breeding water in the same tank.

[0043] The period from the second breeding water transition date and time T2 to the high salinity treatment end date and time Te2 is defined as the high salinity treatment period (T2 to Te2), and the rainbow trout is exposed to high salinity water during this high salinity treatment period (T2 to Te2).

[0044] When rainbow trout that have been reared in freshwater are transferred to a rearing environment of high salinity water such as diluted seawater, it is expected that the rainbow trout will be subjected to osmotic stress because they will be required to have an osmotic pressure adjustment capability that corresponds to the high salinity water. However, in the first embodiment, the trout are transferred to the rearing environment of high salinity water at the date and time T2 when the feeding cessation starts and thereafter the trout are transferred to the second rearing water rearing environment. Therefore, the trout are exposed to the high salinity water in a state where the stress load due to the deterioration of the water quality is alleviated. Therefore, osmotic pressure adjustment can be performed in a state where the resistance to osmotic stress is increased.

[0045] It is desirable that the high salinity treatment period (T2 to Te2) should not exceed three days before the rainbow trout are landed. If the high salinity treatment period (T2 to Te2) exceeds three days before the rainbow trout are landed, there is a risk of the rainbow trout dying (second step S2).

[0046] (3rd step)

[0047] The rainbow trout are landed from the second breeding water at landing date and time T3, which is later than the second breeding water transfer date and time T2 when the breeding water for the rainbow trout is transferred from the first breeding water to the second breeding water. The landing date and time T3 may be the same date and time as the high salinity treatment end date and time Te2, or may be later than the high salinity treatment end date and time Te2.

[0048] In this specification, the term "landing" is used as a concept including immediate killing. Almost at the same time as landing, live-killing or nerve-killing is performed. For example, after landing of rainbow trout, live-killing or nerve-killing is performed on the spot without transportation.

[0049] For example, as shown in Fig. 2(B), the fasting period (T1-Te1) can be set to three days, the two days following the fasting period (T1-Te1) can be set to the high-salinity treatment period (T2-Te2), and the landing can be performed at the same time as the end of the high-salinity treatment. In this case, the end Te1 of the fasting period (T1-Te1) coincides with the start T2 of the high-salinity treatment period (T2-Te2), the end Te2 of the high-salinity treatment period (T2-Te2) coincides with the landing date and time T3, and the landing is performed five days after the start of the fasting (third process S3).

[0050] According to the first embodiment, the treatment is shifted to exposure to high salinity water after the start of fasting. This alleviates the stress load caused by the deterioration of water quality. The stress capacity of the rainbow trout can be allocated to osmotic stress, which is effective in enhancing flavor, by the amount of stress load alleviated. This increases the resistance to osmotic stress load, maximizing the effect of flavor enhancement and reducing the risk of death. Therefore, compared to the conventional method, it is possible to efficiently produce edible fish with high flavor without causing death.

[0051] Each parameter, such as the low salinity of the first rearing water, the high salinity of the second rearing water, the difference in salinity between the first and second rearing waters, the fasting period (T1 to Te1), and the high salinity treatment period (T2 to Te2), can be set while taking into consideration maximizing the flavor enhancement effect and reducing the risk of mortality.

[0052] It is desirable to set each parameter so that the blood osmotic pressure of the rainbow trout increases by 20% or more relative to the blood osmotic pressure during rearing in the first rearing water within a period not exceeding two days after transfer from the first rearing water to the second rearing water. It is also desirable to set each parameter so that the alanine concentration in the muscle of the rainbow trout at the time of landing increases by 1.5 times or more relative to the alanine concentration in the muscle of the rainbow trout when transferred from the first rearing water to the second rearing water.

[0053] (Example)

[0054] An example to which the first embodiment is applied will be described. A test was carried out according to the first embodiment, and the blood osmotic pressure and free amino acids in the muscle of rainbow trout were measured.

[0055] The first rearing water was freshwater, and the second rearing water was 80% diluted seawater (salinity 27‰ or osmotic pressure 800mOsm / kg).

[0056] The fasting period (T1-Te1) was set to three days, and the two days following the fasting period (T1-Te1) were set to the high-salinity treatment period (T2-Te2). The fish were landed at the same time as the end of the high-salinity treatment. The end of the fasting period (T1-Te1) (Te1) was set to coincide with the start of the high-salinity treatment period (T2-Te2) (T2), and the end of the high-salinity treatment period (T2-Te2) (T2) was set to coincide with the landing date and time (T3). The fish were landed five days after the start of the fasting period.

[0057] (Changes in blood osmolarity)

[0058] When the blood osmolality of rainbow trout was measured, the following results were obtained.

[0059] Before transition (at the start of fasting T1): 315 mOsm / kg

[0060] One day after T2, when high salt treatment began: 382 mOsm / kg

[0061] Two days after the start of high salt treatment (T2): 412 mOsm / kg

[0062] One day after the start of the high salinity treatment, T2, the blood osmolality of the rainbow trout increased by 21.2% compared to the blood osmolality (315 mOsm / kg) when they were reared in the first rearing water. Furthermore, two days after the start of the high salinity treatment, T2, the blood osmolality of the rainbow trout increased by 30.7% compared to the blood osmolality (315 mOsm / kg) when they were reared in the first rearing water.

[0063] According to the examples, it was confirmed that within a period not exceeding two days after transferring from the first rearing water to the second rearing water, the blood osmotic pressure of rainbow trout increased by more than 20% compared to the blood osmotic pressure during rearing in the first rearing water.

[0064] It was confirmed that the transfer from freshwater to 80% diluted seawater (salinity 27‰ or osmolality 800mOsm / kg) was sufficient to induce an increase in blood osmolality in rainbow trout.

[0065] (Changes in free amino acid concentration in muscle)

[0066] When the free amino acid concentrations in the muscles of rainbow trout were measured, the results shown in Figures 3, 4, and 5 were obtained.

[0067] Figure 3 shows the change in alanine concentration in muscle. The horizontal axis shows before the transition (T1, the start of fasting), the first day of the transition (one day after T2, the start of high salt treatment), and the second day of the transition (two days after T2, the start of high salt treatment), while the vertical axis shows the alanine concentration (mM) in muscle. The dashed line in the figure shows the taste threshold of 7.1 mM. Alanine is a representative sweet taste substance.

[0068] Figure 4 shows the change in glutamic acid concentration in muscle. The horizontal axis shows before the transition (T1, the start of fasting), the first day of the transition (one day after T2, the start of high salt treatment), and the second day of the transition (two days after T2, the start of high salt treatment), while the vertical axis shows the glutamic acid concentration (mM) in muscle. Glutamic acid is a representative umami taste substance.

[0069] Figure 5 shows the change in anserine concentration in muscle. The horizontal axis shows before the transition (T1, the start of fasting), the first day of the transition (one day after T2, the start of high salt treatment), and the second day of the transition (two days after T2, the start of high salt treatment), while the vertical axis shows the concentration of anserine (mM) in muscle. Anserine is a component that is abundant in the muscles of salmonid fish, and has been reported to have functions such as lowering blood pressure, lowering uric acid levels, anti-inflammation, anti-fatigue, and removing active oxygen.

[0070] According to the examples, the alanine concentration in the muscle of rainbow trout at the start of fasting (T1) was 3.5 (mM), and the alanine concentration in the muscle of rainbow trout on the second day of transfer (T2 at the start of high salinity treatment) was 10 (mM). It was confirmed that the alanine concentration in the muscle of rainbow trout at the time of landing was increased by 1.5 times or more compared to the alanine concentration in the muscle of rainbow trout when transferred from the first rearing water to the second rearing water.

[0071] According to the examples, the alanine concentration (mM) in the muscle of the rainbow trout exceeded the taste threshold of 7.1 mM on or after one day from the start time T2 of the high salt treatment, and it was evaluated that the taste was enhanced.

[0072] According to the examples, it was confirmed that the alanine concentration (mM) in the muscle of rainbow trout continued to increase from the start of the salt treatment, T2, until the second day. Therefore, in order to obtain the effect of improving the flavor of rainbow trout, it is desirable to set the high salt treatment period (T2 to Te2) to 2 days, or to set the period obtained by adding a certain period to 2 days, or to set the period obtained by subtracting a certain period from 2 days.

[0073] In addition to alanine concentrations in the muscle, glutamic acid concentrations in the muscle increased from the start to the end of the high-salt treatment, suggesting that amino acid biosynthesis related to glycolysis and the citric acid cycle was enhanced. No decrease in the antioxidant anserine concentration in the muscle was observed from the start to the end of the high-salt treatment.

[0074] The rainbow trout produced by the production method of the first embodiment is landed after a fasting period, and is characterized in that the osmotic pressure of the blood is 382 mOsm / kg or more.

[0075] Moreover, the rainbow trout produced by the production method of the first embodiment is landed after a fasting period, and is characterized in that the alanine concentration in the muscle is 7.1 mM or more.

[0076] Moreover, from rainbow trout having such characteristics, it can be presumed that the production method thereof is the edible fish production method of the first embodiment.

[0077] In the first embodiment, a method for producing rainbow trout as an edible fish and rainbow trout produced by this production method have been described. However, the first embodiment can be applied to fish species belonging to the Salmonidae family, such as Chum Salmon, Atlantic Salmon, Sockeye Salmon, Coho Salmon, and Chinook Salmon, other than rainbow trout. The first embodiment can also be applied to fish species that can grow in freshwater and seawater, such as eels.

[0078] The first embodiment can also be applied to saltwater fish that cannot grow in freshwater, such as tuna, bonito, horse mackerel, sardines, and pufferfish, and other fish species belonging to the genera Thunnus, Bonito, Smaug, and Pufferfish.

[0079] Furthermore, the first embodiment can be applied to fish species that cannot grow in seawater, such as loach, carp, and crucian carp.

[0080] Second embodiment

[0081] The edible fish targeted in the second embodiment are fish species that cannot grow in seawater.

[0082] Description will be made with reference to FIG. 1, and FIGS. 2(A) and (B) used in the description of the first embodiment.

[0083] (1st step)

[0084] The first tank holds first breeding water, which may be fresh water, for example.

[0085] A predetermined number of edible fish that cannot grow in seawater are housed in a first aquarium. The edible fish are raised while being periodically fed. The first rearing water does not necessarily have to be freshwater, and may be rearing water with a low salinity that is different from the second rearing water. The first rearing water is desirably rearing water with a low salinity of 250 mOsm / kg or less.

[0086] A feeding cessation start date and time T1 is set at a specified date and time before the edible fish are landed, and the supply of feed to the edible fish raised in the first breeding water is stopped during a specified fasting period (T1 to Te1) from the feeding cessation start date and time T1 to the fasting end date and time Te1.

[0087] The fasting period (T1-Te1) should preferably not exceed four days before landing of the food fish.

[0088] The fasting end date and time Te1 may be the start T2, middle, or end Te2 of the high-salinity treatment period (T2 to Te2) described later. It is preferable that the fasting end date and time Te1 is a time when there is no significant deterioration in water quality due to excretion or spitting. The fasting end date and time Te1 may be a time when the risk of death can be reduced and the flavor-improving effect can be enhanced (first step S1).

[0089] (2nd process)

[0090] The edible fish are transferred from the first tank to the second tank at a second water transfer date and time T2 that is later than the feeding stop start date and time T1 when the supply of food to the edible fish is stopped. The second water is stored in the second tank. The second water may have a higher salinity than the first water. The second water is, for example, water with a salinity of 14‰ or an osmotic pressure of 400 mOsm / kg. The second water is preferably water with a high salinity that does not exceed a salinity of 14‰ or an osmotic pressure of 400 mOsm / kg. This is because, depending on the fish species, the blood osmotic pressure may be higher than the osmotic pressure of the second water, and the fish may not be able to survive when the salinity exceeds 14‰ or the osmotic pressure exceeds 400 mOsm / kg.

[0091] The transition from the first breeding water to the second breeding water does not necessarily have to involve a transition from the first tank to the second tank, and may involve replacing the breeding water in the same tank.

[0092] The period from the second breeding water transition date and time T2 to the high salinity treatment end date and time Te2 is defined as the high salinity treatment period (T2 to Te2), and a process of exposing the edible fish to high salinity water is carried out during this high salinity treatment period (T2 to Te2).

[0093] The high salinity treatment period (T2 to Te2) is desirably a period not exceeding three days before the edible fish is landed (second step S2).

[0094] (3rd step)

[0095] The edible fish are landed from the second breeding water at landing date and time T3, which is later than the second breeding water transfer date and time T2 when the breeding water for the edible fish is transferred from the first breeding water to the second breeding water. The landing date and time T3 may be the same date and time as the high salinity treatment end date and time Te2, or may be later than the high salinity treatment end date and time Te2.

[0096] Almost at the same time as landing, the fish is killed by ikijime or nerve-killing. For example, after landing of an edible fish, it is killed or nerve-killed on the spot without transportation.

[0097] For example, as shown in Fig. 2(B), the fasting period (T1-Te1) can be set to three days, the two days following the fasting period (T1-Te1) can be set to the high-salinity treatment period (T2-Te2), and the landing can be performed at the same time as the end of the high-salinity treatment. In this case, the end Te1 of the fasting period (T1-Te1) coincides with the start T2 of the high-salinity treatment period (T2-Te2), the end Te2 of the high-salinity treatment period (T2-Te2) coincides with the landing date and time T3, and the landing is performed five days after the start of the fasting (third process S3).

[0098] According to the second embodiment, the treatment is switched to exposure to high-salinity water after the start of fasting, so stress load due to deterioration of water quality is alleviated and resistance to osmotic stress load is increased. This maximizes the effect of improving the flavor and reduces the risk of death even for edible fish that cannot grow in seawater, and makes it possible to efficiently produce edible fish with high umami taste without causing death compared to the conventional method.

[0099] 6A and 6B are graphs showing the gene expression levels of two types of ALT (alanine aminotransferase) involved in alanine biosynthesis in the muscle of edible fish produced by the edible fish production method of the first embodiment, in comparison with a comparative example.

[0100] Fig. 6A shows a comparison of the ALT of one of the two ALT species with a group of edible fish produced by the edible fish production method of the first embodiment (hereinafter referred to as the seawater transfer group) G11, a group of edible fish of the first comparative example (hereinafter referred to as the pre-transition control group) G21, and a group of edible fish of the second comparative example (hereinafter referred to as the post-transition control group) G22. Fig. 6B shows a comparison of the ALT of the other of the two ALT species with a group of edible fish produced by the edible fish production method of the first embodiment (hereinafter referred to as the seawater transfer group) G12, a group of edible fish of the third comparative example (hereinafter referred to as the pre-transition control group) G23, and a group of edible fish of the fourth comparative example (hereinafter referred to as the post-transition control group) G24.

[0101] Here, the seawater transfer groups G11 and G12 are groups of rainbow trout transferred from a freshwater breeding environment to a seawater breeding environment and landed after a fasting period, for example, a group of 6 rainbow trout. The pre-transfer control groups G21 and G23 are groups of rainbow trout landed in a freshwater breeding environment, for example, a group of 6 rainbow trout. The post-transfer control groups G22 and G24 are rainbow trout transferred from a freshwater breeding environment to a freshwater breeding environment in a separate tank and landed after a fasting period, for example, a group of 6 rainbow trout.

[0102] The vertical axis of Figures 6A and 6B indicates the ALT mRNA expression level / ef1α (×10^3). Note that "10^3" is defined as "10 to the power of 3". ef1α is an internal standard gene, and is used here for standardization when quantifying the ALT mRNA expression level. In the embodiment, the ALT gene expression level is evaluated as the ALT mRNA expression level. The vertical axis of Figures 6A and 6B indicates the average value measured for six rainbow trout samples.

[0103] Comparisons between the seawater transfer groups G11 and G12 and the comparative pre-transfer control groups G21 and G23 and the post-transfer control groups G22 and G24 were performed using Tukey's HSD Test. The significance level was set at 0.05 (5%), and a significance probability P value smaller than the significance level of 0.05 (P<0.05) was judged to be significant. The test was repeated for a sample of six rainbow trout.

[0104] When the ALT mRNA expression levels / ef1α (×10^3) ​​of the seawater transition groups G11 and G12, and the comparative pre-transition control groups G21 and G23 and post-transition control groups G22 and G24 were tested, the significance probability P value was smaller than the significance level of 0.05 (P<0.05), and the results were judged to be significant.

[0105] Therefore, it was revealed that the increase in the gene expression level of ALT of one species in the seawater transfer group G11 in Figure 6A compared to the gene expression level of ALT of one species in the pre-transfer control group G21 in Comparative Example 1 and the post-transfer control group G22 in Comparative Example 2 is statistically significant (not an accidental increase) and is due to the transfer from a freshwater breeding environment to a seawater breeding environment and the fasting period.

[0106] The same is true for Figure 6B, where the increase in the gene expression level of ALT of the other species in the seawater transfer group G12 compared to the pre-transfer control group G23 of Comparative Example 3 and the post-transfer control group G24 of Comparative Example 4 is statistically significant (not an accidental increase), demonstrating that this is due to the transfer from a freshwater breeding environment to a seawater breeding environment and the fasting period that followed.

[0107] In the alanine metabolic pathway in edible fish, for example, rainbow trout, the gene expression level of ALT, an enzyme involved in the biosynthesis of alanine, increases significantly compared to the comparative example after a fasting period when the fish are transferred from a freshwater rearing environment to a seawater rearing environment. From this result, it is considered that the biosynthesis of alanine is promoted with the transfer to a seawater environment after the fasting period, and the amount of alanine accumulated in the muscle of rainbow trout increases significantly compared to the comparative example.

[0108] The above results suggest that the ALT gene expression level is involved in the increase in the amount of alanine accumulated. Alanine, a free amino acid, is deeply involved in the taste (sweetness) of rainbow trout. Therefore, the group of rainbow trout in which the ALT gene expression level is significantly increased compared to the comparative example can be identified as a group of rainbow trout with improved taste (sweetness) produced by the edible fish production method of the first embodiment.

[0109] FIG. 7 is a graph showing the plasma osmotic pressure of edible fish produced by the edible fish production method of the first embodiment in comparison with a comparative example.

[0110] Similar to Figures 6A and 6B, Figure 7 compares the seawater migration group G13 produced using the edible fish production method of the first embodiment, the pre-migration control group G25 of the fifth comparative example, and the post-migration control group G26 of the sixth comparative example.

[0111] The vertical axis of FIG. 7 represents plasma osmolality (mOsm / kg).

[0112] Seawater migration group G13 is the same population as seawater migration groups G11 and G12 shown in Figures 6A and 6B. Seawater migration group G13 is the same population as seawater migration groups G11 and G12 shown in Figures 6A and 6B. Pre-transition control group G25 is the same population as pre-transition control groups G21 and G23 shown in Figures 6A and 6B. Post-transition control group G26 is the same population as post-transition control groups G22 and G24 shown in Figures 6A and 6B.

[0113] Figure 7 shows that the average plasma osmolality of the seawater transition group G13 was 383 mOsm / kg, which is increased compared to the average plasma osmolality of the pre-transition control group G25 in the fifth comparative example, 303 mOsm / kg, and the average plasma osmolality of the post-transition control group G26 in the sixth comparative example, 308 mOsm / kg.

[0114] The increase in plasma osmolality in seawater transition group G13 shown in Figure 7 is due to exposure to high-salinity water, and indicates that alanine as a free amino acid in muscle increases in order to reduce the osmotic pressure difference between plasma and cells.

[0115] Therefore, as shown in Figures 6A and 6B, the group of rainbow trout in which the gene expression level of ALT is increased compared to the comparative example, and as shown in Figure 7, the group of rainbow trout in which the plasma osmotic pressure is increased compared to the comparative example, is a group of rainbow trout in which alanine is biosynthesized by ALT in the alanine metabolic pathway within the individual rainbow trout, resulting in increased alanine in the muscle, and can be identified as a group of rainbow trout with enhanced taste (sweetness) produced by the production method of the first embodiment.

[0116] The disclosure of Japanese Patent Application No. 2022-002458, filed on January 11, 2022, is incorporated by reference in its entirety into this specification.

Claims

1. A step of breeding the edible fish contained in the first breeding water by periodically supplying them with food; a first step of determining a feeding stop start date and time at a predetermined date and time before the edible fish are landed, and stopping the supply of feed to the edible fish reared in the first rearing water from the feeding stop start date and time; a second step of transferring the breeding water of the edible fish from the first breeding water to a second breeding water having a salinity higher than that of the first breeding water after stopping the supply of food to the edible fish; a third step of transferring the breeding water of the edible fish from the first breeding water to the second breeding water, and then unloading the edible fish from the second breeding water; 16. A method for producing food fish, comprising:

2. The fasting period during which food supply was suspended before landing did not exceed four days; 2. A method for producing edible fish according to claim 1.

3. The high salinity treatment period in which the fish are reared in the second rearing water before landing is not longer than 3 days.

3. A method for producing edible fish according to claim 1 or 2.

4. A first step of stopping the supply of feed to the edible fish reared in the first rearing water; a second step of transferring the breeding water of the edible fish from the first breeding water to a second breeding water having a salinity higher than that of the first breeding water after stopping the supply of food to the edible fish; a third step of transferring the breeding water of the edible fish from the first breeding water to the second breeding water, and then unloading the edible fish from the second breeding water; A method for producing edible fish, comprising: Within a period not exceeding two days after the transfer from the first rearing water to the second rearing water, the blood osmotic pressure of the edible fish increases by 20% or more compared to the blood osmotic pressure during rearing in the first rearing water. Methods of producing food fish.

5. A first step of stopping the supply of feed to the edible fish reared in the first rearing water; a second step of transferring the breeding water of the edible fish from the first breeding water to a second breeding water having a salinity higher than that of the first breeding water after stopping the supply of food to the edible fish; a third step of transferring the breeding water of the edible fish from the first breeding water to the second breeding water, and then unloading the edible fish from the second breeding water; A method for producing edible fish, comprising: the alanine concentration in the muscle of the edible fish at the time of landing is increased to 1.5 times or more compared to the alanine concentration in the muscle of the edible fish when transferred from the first rearing water to the second rearing water; Methods of producing food fish.

6. The first rearing water is fresh water or rearing water having a low salinity and an osmotic pressure of 250 mOsm / kg or less. A method for producing edible fish according to any one of claims 1 to 5.

7. The edible fish is a fish species that can grow in freshwater and seawater; 7. A method for producing edible fish according to claim 6.

8. The edible fish is a fish species belonging to the Salmonidae family.

8. A method for producing edible fish according to claim 7.

9. The food fish is rainbow trout.

9. A method for producing edible fish according to claim 8.

10. The second rearing water is rearing water having a high salinity, that is, a salinity of 27‰ or more or an osmotic pressure of 800 mOsm / kg or more. A method for producing edible fish according to any one of claims 6 to 9.

11. The edible fish is a fish species that cannot grow in seawater. A method for producing edible fish according to any one of claims 1 to 5.

12. The second rearing water is rearing water having a high salinity, the salinity of which does not exceed 14‰ or the osmotic pressure of which does not exceed 400 mOsm / kg.

12. A method for producing edible fish according to claim 11.

13. 11. The method for producing edible fish according to any one of claims 1 to 10, which produces edible fish including rainbow trout having a blood osmolality of 382 mOsm / kg or more.

14. 14. The method for producing edible fish according to any one of claims 1 to 10 and 13, which produces edible fish, including rainbow trout, having an alanine concentration in muscle of 7.1 mM or more.

15. An edible fish including rainbow trout is caught after being reared in a first rearing water while being periodically supplied with food, and after having undergone a fasting period and a step of being transferred to a second rearing water having a higher salt concentration than the first rearing water after the start of the fasting period, and the osmotic pressure of the blood is 382 mOsm / kg or more.

16. An edible fish including rainbow trout is caught after undergoing a fasting period in which it is reared in a first rearing water while being periodically supplied with food, and a step of transferring it to a second rearing water having a higher salt concentration than the salt concentration of the first rearing water after the start of the fasting period, and has an alanine concentration in its muscles of 7.1 mM or more.

17. An edible fish, including rainbow trout, which has been transferred from a freshwater breeding environment to a saltwater breeding environment, raised while being periodically supplied with food, then subjected to a fasting period, and then harvested, and which shows a significant increase in the gene expression level of ALT (alanine aminotransferase), which is involved in the biosynthesis of alanine in the muscle, compared to the same species of edible fish.

18. The fasting period during which food supply was suspended before landing did not exceed four days; 5. A method for producing edible fish according to claim 4.

19. The high salinity treatment period in which the fish are reared in the second rearing water before landing is not longer than 3 days.

20. A method for producing edible fish according to claim 4 or 18.

20. The fasting period during which food supply was suspended before landing did not exceed four days; 6. A method for producing edible fish according to claim 5.

21. The high salinity treatment period in which the fish are reared in the second rearing water before landing is not longer than 3 days.

21. A method for producing edible fish according to claim 5 or 20.

22. A period not exceeding two days after the transfer from the first rearing water to the second rearing water the blood osmotic pressure of the edible fish increases by 20% or more within a period of time compared to the blood osmotic pressure during breeding in the first breeding water; 22. A method for producing edible fish according to any one of claims 5, 20 and 21.

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