Method for producing a feed additive for imparting the aroma of kabosu to the meat of fish of the genus Yellowtail, and aquaculture method using aquaculture feed containing the feed additive for fish of the genus Yellowtail.

Abstract

This invention provides a yellowtail aquaculture feed that is excellent at imparting the aroma of kabosu citrus and can prevent skin disorders in yellowtail fish, as well as an additive that can produce said feed, and an aquaculture method using the aquaculture feed containing said feed additive. [Solution] A feed additive for imparting the aroma of kabosu to the meat of yellowtail fish, comprising kabosu essential oil as an active ingredient. Preferably, the kabosu essential oil is obtained by steam distillation using kabosu peel as a raw material. Preferably, it is also used to prevent skin disorders in yellowtail fish. The present invention further provides yellowtail aquaculture feed and aquaculture method using kabosu essential oil.

Description

[Technical Field]

[0001] The present invention relates to an additive added to feed for fish of the genus *Seriola* to impart the aroma of *Citrus sphaerocarpa* (Kabosu) to the flesh of fish of the genus *Seriola*, and to an aquaculture method using aquaculture feed that employs said feed additive for fish of the genus *Seriola*. [Background Art]

[0002] Conventionally, for producing yellowtail having the flavor of Kabosu (sometimes referred to as "Kabosu yellowtail"), a method for culturing yellowtail has been practiced in which Kabosu peel powder obtained after pressing Kabosu fruit juice is added to feed (Non-Patent Document 1). In addition, Patent Document 1 describes a feed for cultured fish characterized in that peel oil, which is collected from Iyokan peel by a pressing method and crudely purified without distillation, is added. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2016-32448 [Non-Patent Literature]

[0004] [Non-Patent Document 1] https: / / feis.fra.affrc.go.jp / event / 6th_forum / 6th_forum_h27houkoku / 03_kiyabu.pdf, retrieved on February 5, 2025 [Summary of the Invention] [Problem to be Solved by the Invention]

[0005] In recent years, feeding semi-solid feed has been mainstream for the culture of Kabosu yellowtail, but switching to solid feed is being studied in consideration of the environment and other factors. However, it has been found that when the Kabosu peel powder described in Non-Patent Document 1 is added to solid feed in an amount equivalent to that used for conventional semi-solid feed, skin disorders occur in yellowtail, and progression of said skin disorders leads to death of fish of the genus *Seriola*. On the other hand, Patent Document 1 does not address the problem of imparting the aroma of kabosu to yellowtail meat while avoiding skin damage. [Means for solving the problem]

[0006] The inventors of this invention have discovered that by using kabosu essential oil, it is possible to effectively impart the scent of kabosu to yellowtail while avoiding skin irritation, thus completing the present invention.

[0007] In other words, the present invention provides a feed additive for imparting the aroma of kabosu to the meat of fish of the genus Yellowtail, which contains kabosu essential oil as an active ingredient.

[0008] The present invention also provides a feed for farming fish of the genus Yellowtail, which contains kabosu essential oil.

[0009] The present invention also provides a method for producing feed for farming yellowtail fish, which involves adding the aforementioned fragrance-imparting feed additive to the raw materials for farmed fish feed.

[0010] The present invention also provides a method for producing farmed yellowtail fish that have been given the aroma of kabosu, comprising the step of feeding the aforementioned aquaculture feed to yellowtail fish. Furthermore, the present invention provides a method for cultivating fish of the genus Yellowtail, comprising the step of feeding the aforementioned aquaculture feed to fish of the genus Yellowtail. Furthermore, the present invention provides a fish of the genus Yellowtail that has been imparted with the aroma of kabosu citrus, obtained by the above-mentioned manufacturing method. [Effects of the Invention]

[0011] The present invention provides a farming feed for yellowtail fish that is excellent in imparting the aroma of kabosu and can prevent skin disorders, a method for producing the farming feed, and an additive that can be used to obtain the feed. Furthermore, the present invention provides a farming method for yellowtail fish that can produce farmed yellowtail fish that are imparted with the aroma of kabosu while preventing skin disorders, a method for producing yellowtail fish, and yellowtail fish obtained by the method. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a graph showing the trend in the average weight of yellowtail genus fish during aquaculture. [Figure 2] Figure 2 is a photograph showing skin damage in a fish of the genus Sargassum. It can be seen that redness is present due to skin damage from the head to the back. [Figure 3] Figure 3 is a graph showing the changes in limonene levels in the muscles of fish belonging to the genus Sargassum. [Modes for carrying out the invention]

[0013] The following describes preferred embodiments of the present invention. [1] Feed additive for imparting the aroma of kabosu to the meat of fish of the genus Yellowtail. The feed additive for imparting the aroma of kabosu to the meat of yellowtail fish of the present invention (hereinafter simply referred to as "feed additive") contains kabosu essential oil. The following description of kabosu essential oil all pertains to the description of the feed additive of the present invention.

[0014] According to the present invention, it is possible to prevent skin disorders in fish of the genus Yellowtail that sometimes occurred when kabosu peel powder was conventionally used as solid feed. The inventor speculates that one reason for this is as follows: Kabosu peel contains a certain amount (e.g., 7 ppm by mass) of furanocoumarins such as bergapten, which are considered to be phototoxic, and in kabosu peel powder, the amount of furanocoumarins increases (e.g., 47 ppm by mass) due to juicing and drying. Therefore, fish of the genus Yellowtail ingest a large amount of furanocoumarins from feed containing a large amount of kabosu peel powder. Studies on humans have shown that phototoxicity from furanocoumarins causes pain, redness and inflammation of the skin in areas exposed to sunlight, and sometimes discoloration of the skin to brown or bluish-gray. There are concerns that similar disorders may occur in fish of the genus Yellowtail. Therefore, it is thought that in fish of the genus Yellowtail, skin disorders may occur due to phototoxicity caused by the accumulation of furanocoumarins in the body. On the other hand, kabosu essential oil obtained by pressing has a relatively high content of furanocoumarins such as bergapten (for example, about 1480 ppm by mass), but the content of furanocoumarins can be significantly reduced in kabosu essential oil obtained by steam distillation in particular (for example, about 5.8 ppm by mass). Furthermore, since kabosu essential oil contains high concentrations of volatile oil components such as limonene and myrcene, which are considered to be active ingredients that impart the flavor of kabosu, less is needed to add it to the feed for yellowtail fish to give them a kabosu flavor. In addition, in the case of Iyokan described in Patent Document 1, the amount of furanocoumarins in the peel is significantly less than in kabosu, so if furanocoumarins were the cause of skin disorders, this problem is unlikely to occur in Iyokan. To the best of the applicant's knowledge, it was previously unknown that components derived from citrus peels, such as peel powder, could cause skin disorders in yellowtail fish.

[0015] Examples of fish of the genus *Seriola* include *Seriola quinqueradiata* (Japanese amberjack), *Seriola dumerili* (greater amberjack), *Seriola lalandi* (yellowtail amberjack), and *Seriola rivoliana* (longfin yellowtail). Among these, from the viewpoints of economic efficiency and demand, the present invention preferably targets Japanese amberjack as the fish of the genus *Seriola*.

[0016] Raw materials for kabosu essential oil include kabosu fruits (exocarp (flavedo), endocarp (albedo), pulp, fruit juice, seeds, etc.), flowers, leaves, and tree trunks. One or more selected from kabosu fruits, specifically exocarp (flavedo), endocarp (albedo), pulp, and fruit juice, are particularly preferable, and inclusion of kabosu exocarp (flavedo) is especially preferable from the viewpoint of a high effect of imparting kabosu fragrance. The proportion of kabosu exocarp (flavedo) in the raw material for kabosu essential oil is preferably 20% by mass or more, and more preferably 30% by mass or more. In kabosu after juicing, the proportion of kabosu exocarp is generally 20% by mass or more. Hereinafter, the simple term "pericarp" refers to exocarp.

[0017] Essential oil refers to a volatile oil extracted from a plant body that has an aromatic fragrance. Essential oils are generally produced through a step by one or more methods selected from pressing methods, distillation methods, and solvent extraction methods. The pressing method is a method for extracting essential oil by pressing a plant. For example, citrus essential oil components accumulate in oil glands in the tissues on the surface of the pericarp. Strong pressure is applied to the pericarp with mechanical rollers to crush these oil glands and squeeze out the essential oil.

[0018] Examples of distillation methods include steam distillation and CO2 distillation. In steam distillation, plant material is placed in a heating vessel and heated with steam or water. Heat opens the oil glands on the pericarp surface and releases the oil together with the steam. Thereafter, this mixture of steam and oil passes through a cooling device and returns to a liquid state. This liquid is composed of oil and water, separates naturally, and the upper-phase oil is collected as the essential oil. CO2 distillation is an extraction method that uses carbon dioxide (CO2) under high pressure. Under high pressure, carbon dioxide enters a state called "supercritical," where it possesses properties of both liquid and gas. Supercritical carbon dioxide penetrates the plant material, extracting aromatic components. After the pressure is released, the carbon dioxide returns to a gaseous state, leaving behind the essential oil. This method can produce essential oils of very high purity and, because it does not use heat, can also extract heat-sensitive components, but it requires large-scale equipment.

[0019] Furthermore, solvent extraction is a method of extracting components contained in the raw material plant using organic solvents. Essential oil components are easily soluble in lipid-soluble components, so they are extracted by dissolving them in organic solvents. The essential oil components dissolved in the organic solvent are obtained as a semi-solid component called "concrete" when the organic solvent evaporates. This contains waxes and other substances along with the essential oils, so ethanol is added to separate the waxes and other substances, and then the ethanol is removed to obtain the essential oils.

[0020] In this invention, it is preferable to use kabosu essential oil that has undergone steam distillation, as this effectively reduces the amount of phototoxic components called furanocoumarins derived from citrus fruits. Furthermore, steam distillation has the advantage of being less prone to contamination by impurities, thus minimizing the deterioration of essential oil quality.

[0021] Steam distillation methods include water-steam distillation, steam distillation, and water distillation. Water steam distillation is a distillation method in which a mesh is placed at the bottom of a still, plants are placed on top of the mesh and water is placed below the mesh, the water is heated and the steam is passed through the plants. Steam distillation is a distillation method in which steam is generated separately from the still and the heated steam is poured into the plant in the still. Furthermore, water distillation is a distillation method in which plants are heated while submerged in water. In these distillation methods, the boiling point may be lowered by creating a vacuum inside the equipment. Alternatively, cohovation (redistillation) may be performed, in which the distilled water obtained once is used for distillation again.

[0022] In the present invention, water distillation is preferred in terms of distillation efficiency and workability, and in particular, performing water distillation on a mixture of water and plant material is preferred in terms of distillation efficiency. When performing water distillation, it is preferable to distill the kabosu used as raw material while it is immersed in 200 to 250 parts by mass of water per 100 parts by mass of kabosu, and more preferably while it is immersed in 210 to 240 parts by mass of water. The preferred pressure conditions inside the still during distillation are -72,600 to -67,000 PaG, and more preferably -71,000 to -69,000 PaG. The internal temperature of the kettle is preferably 65-75°C, and more preferably 68-72°C.

[0023] The resulting kabosu essential oil typically contains a large amount of terpenes. Here, terpenes include terpenes and terpenoids. Terpenes are hydrocarbons, including monoterpenes, sesquiterpenes, and diterpenes. Terpenoids refer to compounds in which an OH group or aldehydes are introduced to a terpene. The kabosu essential oil preferably contains 85% by mass or more of terpenes, more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0024] In particular, kabosu essential oil is preferred because its high terpene content is characteristic of the kabosu flavor, with a terpene content of 85% by mass or more being preferred, more preferably 90% by mass or more, and especially preferred 95% by mass or more. In particular, kabosu essential oil is preferred because its high monoterpene content is characteristic of the kabosu flavor, with a monoterpene content of 85% by mass or more being preferred, 90% by mass or more being more preferred, and 95% by mass or more being particularly preferred.

[0025] In kabosu essential oil, it is preferable that limonene accounts for 55% or more by mass, more preferably 60% or more by mass, and particularly preferably 65% ​​or more by mass, in order to express the characteristic flavor of kabosu. Furthermore, it is preferable that the limonene content of kabosu essential oil is 94% or less by mass, more preferably 90% or less by mass, and particularly preferably 80% or less by mass. In this specification, limonene preferably refers to d-limonene.

[0026] In kabosu essential oil, it is preferable that the myrcene content is 5% by mass or more, more preferably 8% by mass or more, and particularly preferably 12% by mass or more, in order to express the characteristic flavor of kabosu. Furthermore, it is preferable that the myrcene content is 30% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less. In this specification, myrcene preferably refers to β-myrcene.

[0027] Furthermore, it is preferable that the kabosu essential oil contains 1% by mass or more of γ-terpinene, more preferably 1.5% by mass or more, and particularly preferably 2% by mass or more, as this expresses the characteristic flavor of kabosu. It is also preferable that the γ-terpinene content is 10% by mass or less, more preferably 8% by mass or less, and particularly preferably 5% by mass or less.

[0028] Furthermore, in kabosu essential oil, it is preferable that the p-cymene content is typically 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more, in order to express the characteristic flavor of kabosu. In addition, it is preferable that the p-cymene content is 6% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass or less.

[0029] Furthermore, the kabosu essential oil preferably contains 0.1% by mass or more of α-pinene, more preferably 0.5% by mass or more in terms of expressing the characteristic flavor of kabosu, and particularly preferably 1% by mass or more. In addition, the α-pinene content preferably contains 6% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass or less.

[0030] Furthermore, it is preferable that the kabosu essential oil contains 0.1% by mass or more of β-farnesene, which is desirable for expressing the characteristic flavor of kabosu, and more preferably 0.5% by mass or more. It is also preferable that the β-farnesene content is 5% by mass or less, and more preferably 2% by mass or less.

[0031] Furthermore, the kabosu essential oil preferably contains at least 0.05% by mass of one or more compounds selected from β-caryophyllene, β-pinene, β-phellandrene, and decanal in total, more preferably at least 0.1% by mass, particularly preferably at least 0.2% by mass, more preferably at least 4% by mass, and particularly preferably at least 3% by mass. Each of these four compounds may also be present individually in amounts of 0.05% by mass or more, 0.1% by mass or more, 0.2% by mass or more, or 4% by mass or less, or 2% by mass or less.

[0032] The aforementioned composition of kabosu essential oil can be obtained by steam distillation, particularly by adjusting the mixing ratio of raw materials and water, heating temperature, and pressure conditions in a steam distillation method that includes a water distillation step.

[0033] The kabosu essential oil preferably contains 5 ppm by mass or less of the phototoxic bergapten, and more preferably 2 ppm by mass or less. Bergapten is a representative component of the phototoxic furanocoumarins found in the peel of the kabosu fruit. Furthermore, it is preferable that the total content of furanocoumarins selected from bergapten, isopimpinelin, psoralen, and bergamotin be 10 ppm by mass or less, and more preferably 5 ppm by mass or less. To keep the furanocoumarin content below the aforementioned range, kabosu essential oil can be produced using steam distillation.

[0034] For the component analysis of essential oils, a gas chromatograph-mass spectrometer can be used. The sample should be the essential oil without dilution. The analysis conditions can involve using a db-WAX UI column (60 m length, 0.25 mm inner diameter, 0.25 μm film thickness) and a temperature program that increases from 80°C to 240°C at a rate of 3°C / min, maintaining the temperature for 87 minutes. The injection port temperature can be 250°C, the injection volume 0.2 μl, and the split ratio 300:1. The carrier gas can be helium at a flow rate of 1 ml / min. The detector is a mass spectrometer, and the detector temperature can be set to 230°C. Suitable measuring instruments include Agilent Technologies, Inc. models such as the 7890B and 5977A. Furthermore, high-performance liquid chromatography (HHL) can be used for the analysis of furocoumarins. For the analysis, a Nucleosil 100-5 column (250 mm in length, 4.6 mm in inner diameter) can be used, with N-hexane and 2-propyl alcohol as the eluent, in a volume ratio of 99:1, a flow rate of 1.8 ml / min, and a column temperature of 40°C. An Agilent Technologies 1260 Infinity or similar instrument can be used for measurement.

[0035] The additive of the present invention is preferably used to prevent skin disorders in fish of the genus Yellowtail. Prevention, as used herein, includes both prevention and symptom reduction. Examples of skin disorders include skin disorders associated with the ingestion of kabosu or its processed products, and preferably skin disorders associated with the ingestion of kabosu peel or its processed products. Symptoms include, for example, redness, inflammation, and peeling of the skin.

[0036] [Feed for farming fish of the genus Yellowtail] Feed used in aquaculture can be divided into feed and bait. Feed refers to raw fish or shrimp given directly to the fish, while bait refers to artificial feed. Examples of feed used in aquaculture of the yellowtail genus include moist pellets (MP) and extruder pellets (EP). Moist pellets are a type of moist, semi-moist solid feed, usually obtained by mixing live feed and fish meal. In contrast, extruder pellets refer to solid feed formed by an extruder. They are manufactured using an extruder at high temperature and pressure, and due to expansion during extrusion, they are usually formed as porous materials. Extruder pellets are dry feed, have even higher nutritional value than MP (moist pellets), can be stored for a long time, do not crumble when placed in water, float for a while before slowly sinking, resulting in less leftover food, a smaller burden on the fishing grounds, and good digestibility and absorption.

[0037] The aquaculture feed used in this invention preferably contains extruder pellets because it has a lower environmental impact, is highly storable, and allows essential oils to be retained in the porous structure when added externally, resulting in good retention.

[0038] Aquaculture feed containing kabosu essential oil and extruder pellets preferably has a moisture content of 15.0% by mass or less, which is preferable in terms of low environmental impact and shelf life, and more preferably 12.0% by mass or less. The moisture content of aquaculture feed can be measured, for example, by a method of heating and drying at atmospheric pressure.

[0039] Furthermore, the feed for aquaculture has a bulk density of 0.80 g / cm³. 3 The above is preferable in terms of the sinking properties of the aquaculture feed, which is 0.90 g / cm 3 It is particularly preferable that the above conditions are met. Furthermore, the bulk density of the aquaculture feed should be 1.00 g / cm³. 3 The following characteristics are particularly preferable because they allow the material to sink slowly, making it easy for fish of the genus Yellowtail to eat, and because it is easily formed into a porous structure, resulting in good essential oil retention. The bulk density is measured by the following method. The sample is placed in a cylindrical container with a volume of 1000 ml (axial length 42 cm) until it overflows, and the excess sample on the top of the container is scraped off. The mass (g) of the sample is measured by subtracting the mass of the empty container, which has been measured beforehand. The bulk density is then calculated from this measurement result.

[0040] The longitudinal length of the feed for aquaculture is preferably 8 to 18 mm, and more preferably 10 to 15 mm. The longitudinal direction is the direction in which the longest transverse segment of the projection image extends when the feed is placed with any surface facing downwards and light is projected from above. Furthermore, the projection direction length perpendicular to such longest transverse segment is preferably 6 to 18 mm, and more preferably 8 to 15 mm. For example, in the case of a cylindrical shape that is long in the axial direction, the longitudinal direction is the axial length, and the projection direction length perpendicular to the axial length is the radial direction of the cylinder.

[0041] Examples of the composition of pelletized feed ingredients for aquaculture include those containing 45-75% by mass, particularly 50-70% by mass, of fish meal; 6-25% by mass, particularly 10-22% by mass, of soybean oil meal and corn gluten meal in total; 5-25% by mass, particularly 8-20% by mass, of grains (wheat flour, starch, etc.); and 5-25% by mass, particularly 8-20% by mass, of other components such as fish oil. The pelletized feed ingredients for aquaculture preferably have a crude fat content of 10% by mass or more, and more preferably 12% by mass or more.

[0042] For the aquaculture feed of fish of the genus Yellowtail, it is preferable to contain 0.05% by mass or more of kabosu essential oil, more preferably 0.075% by mass or more, and particularly preferable 0.14% by mass or more, from the standpoint of flavoring. Furthermore, for the aquaculture feed of fish of the genus Yellowtail, it is preferable to contain 0.30% by mass or less of kabosu essential oil, and more preferably 0.16% by mass or less, from the standpoint of cost, as further addition of kabosu essential oil is not expected to improve the flavor.

[0043] Furthermore, the present invention preferably provides a method for producing aquaculture feed for fish of the genus Yellowtail by adding the aforementioned fragrance-imparting feed additive to aquaculture feed raw materials. For example, extruder pellets can be used as aquaculture feed raw materials. When mixing the aquaculture feed raw materials and the fragrance-imparting feed additive, the aquaculture feed raw materials and oils other than kabosu essential oil are preferably mixed in a mass ratio of 100:0.5 to 11.6, more preferably 100:0.5 to 11.2, and at that time, kabosu essential oil is mixed in an amount of 0.05% by mass or more and 0.30% by mass or less of the total feed. The mixing of the aquaculture feed raw materials and the fragrance-imparting feed additive can be done using a commercially available mixer, and specifically, an electric concrete mixer can be used. According to this method, since the fragrance-imparting feed additive is added to the cooled pellets after manufacturing, rather than during extruder manufacturing, deterioration of flavor due to heating during extruder manufacturing can be prevented, and the kabosu fragrance-imparting feed additive can be easily added to the feed.

[0044] As for oils other than kabosu essential oil, oils that are liquid at 25°C are preferred in terms of the dispersibility of kabosu essential oil. Any oil can be used from fish oil, vegetable oil, or animal oil other than fish oil, but the inclusion of fish oil is preferred because it is highly palatable to fish of the genus Yellowtail. When extruder pellets are used as raw materials in the above method, dispersing and retaining kabosu essential oil in the porous substrate of the extruder pellets makes them less susceptible to water penetration. The addition of oil also increases the time it takes for the air inside the pellets to be replaced by water, causing the extruder pellets to sink slowly, which is thought to make them easier for fish of the genus Yellowtail to eat. The extruder pellets preferably have a moisture content of 12.0% by mass or less, and more preferably 10.0% by mass or less. Furthermore, the bulk density should be 0.8 g / cm³. 3 More than 1.00g / cm 3 Preferably, it is 0.90 g / cm³. 3 More than 1.00g / cm 3 The following is more preferable: The moisture content and bulk density of aquaculture feed can be within the same range as those of extruder pellets.

[0045] It is preferable to add 0.05 parts by mass or more of kabosu essential oil per 100 parts by mass of pelletized aquaculture feed raw material, more preferably 0.075 parts by mass or more, and particularly preferably 0.14 parts by mass or more. Furthermore, for aquaculture feed for fish of the genus Yellowtail, it is preferable to add 0.30 parts by mass or less of kabosu essential oil per 100 parts by mass of pelletized aquaculture feed raw material, and more preferably 0.16 parts by mass or less, as further addition to these amounts is not expected to improve the flavor and also from a cost perspective.

[0046] (Cultivation method) In aquaculture, it is desirable to feed yellowtail fish with added kabosu essential oil within three months, or more preferably within two months, immediately before harvesting. The general method for farming yellowtail involves natural spawning in February and March of the first year, raising juvenile yellowtail in April and May, and then farming them for about one to one and a half years starting in June. The feed for farming yellowtail fish, to which kabosu essential oil has been added, is preferably administered to yellowtail fish over a certain period of time, preferably for four consecutive weeks, preferably for five consecutive weeks, and more preferably for seven consecutive weeks. The amount of feed to be given is preferably 0.5 to 3% by mass of the weight of the fish of the genus Sargassum, and more preferably 1 to 2.5% by mass.

[0047] When feeding yellowtail fish with feed containing kabosu essential oil, it is desirable to divide the feeding into at least two times a week, or at least eight times in total, preferably at least two times a week, or at least ten times in total, and more preferably at least three times a week, or at least fourteen times in total.

[0048] Among yellowtail species fed with aquaculture feed supplemented with kabosu essential oil, zero- to two-year-old fish are suitable, but one- to two-year-old fish are particularly preferable in terms of market size. [Examples]

[0049] (Preparation of Kabosu essential oil) The kabosu essential oil used had the following composition. It was obtained by the following procedure. 450 kg of kabosu (with the peel as the main component (containing 30% or more by mass), including seeds and juice) after juicing was mixed with 1000 kg of water. Steam distillation was performed by reducing the pressure to -70,000 PaG and heating the still. The internal temperature of the still reached 70°C. The steam generated by the steam distillation was cooled, and only the upper phase oil was separated from the resulting distillate to obtain kabosu essential oil with the composition shown in Table 1. The bergapten content in the kabosu essential oil was 0.4 ppm by mass.

[0050] [Table 1]

[0051] (Feed preparation) <Example 1> Compound feed (Hamachi EP Friend: manufactured by Nisshin Marubeni Feed Co., Ltd., cylindrical shape, axial length 15 mm, diameter 15 mm, moisture content 12.0% by mass, bulk density 0.9 cm³) 3 90.0 parts by weight of kabosu essential oil, 0.15 parts by weight of feed oil, and 10.0 parts by weight of feed oil (Nice Feed Oil C: manufactured by Ueda Oil Co., Ltd.) were mixed using a resealable plastic bag.

[0052] <Example 2> 90.0 parts by weight of compound feed (Hamachi EP Friend: manufactured by Nisshin Marubeni Feed Co., Ltd.), 0.30 parts by weight of kabosu essential oil, and 10.0 parts by weight of feed oil (Nice Feed Oil C: manufactured by Ueda Oil Co., Ltd.) were mixed using a resealable plastic bag.

[0053] <Comparative Example 1> 98.14 parts by weight of compound feed (Hamachi EP Friend: manufactured by Nisshin Marubeni Feed Co., Ltd.), 1.5 parts by weight of kabosu peel powder, and 0.39 parts by weight of spreading agent (Apifac-W 1K: manufactured by Kokin Chemical Co., Ltd.) were mixed using an electric concrete mixer.

[0054] (Cultivation method) One-year-old yellowtail fish, each weighing approximately 4 kg at the time of landing, were divided into four experimental groups of 11 fish each. Each experimental group was fed the feeds of Examples 1 and 2 and Comparative Example 1. In Examples 1 and 2, the fish were fed a feed equivalent to 2% by mass of their body weight once a day, three times a week, for seven weeks until they were full. For the two weeks following the seven weeks, they were fed compound feed (Hamachi EP Friend: manufactured by Nisshin Marubeni Feed Co., Ltd.). Comparative Example 1 was fed a feed equivalent to 2% by mass of body weight once a day, three times a week, for five weeks until it was saturated. Damage to the skin of the yellowtail occurred at the five-week mark, so compound feed was given from weeks 6 to 9.

[0055] (Average weight of yellowtail genus in aquaculture) In both Examples 1 and 2 and Comparative Example 1, the weight of three fish in each test group was measured 5, 7, and 9 weeks after the start of cultivation, and the average weight was recorded. The results are shown in Figure 1. As shown in Figure 1, the weights in all of Examples 1 and 2 and Comparative Example 1 were within an acceptable range.

[0056] (Checking for skin damage) In both Examples 1 and 2 and Comparative Example 1, the presence or absence of skin disorders in all fish in each test group was checked 5, 7, and 9 weeks after the start of cultivation. The results are shown in Table 2. As shown in Table 2, in Examples 1 and 2, no skin disorders were observed in any of the yellowtail species even after 9 weeks from the start of cultivation. In Comparative Example 1, although there were individual differences in the degree of skin damage, skin disorders were observed in all species of the genus *Bryophyllum* after 5 weeks.

[0057] [Table 2]

[0058] (Sensory evaluation of fish meat with kabosu flavor) In both Examples 1 and 2 and Comparative Example 1, the flavor and acidity of kabosu citrus fruit were checked in three fish from each test group 5, 7, and 9 weeks after the start of cultivation. Ten panelists evaluated the results according to the following criteria. The average results are shown in Tables 3 and 4. (Flavor evaluation criteria) 4: You can faintly taste the flavor of kabosu (a type of citrus fruit). 3: You can really taste the kabosu flavor. 2: The kabosu flavor is very strong. 1: The kabosu flavor is very strong.

[0059] (Criteria for evaluating acidity) 4: You can taste a slight sourness from the kabosu citrus. 3: You can really taste the tartness of the kabosu citrus. 2: The tartness of the kabosu is quite strong. 1: The tartness of the kabosu is very strong.

[0060] For the yellowtail to be considered "kabosu yellowtail," it is necessary that it retains the flavor of kabosu during the period between 7 weeks of cultivation and shipment. As shown in Table 3, both Examples 1 and 2 possessed all the qualities of "kabosu yellowtail" (yellowtail with kabosu flavor).

[0061] [Table 3]

[0062] Furthermore, as shown in Table 4, both Examples 1 and 2 possessed all the qualities of kabosu yellowtail (yellowtail with the sourness of kabosu citrus). [Table 4]

[0063] (Checking the limonene content of fish meat) As one way to determine if a fish had a kabosu-like flavor, the d-limonene content in the fish meat was measured. Specifically, 20g of muscle from the left flank near the head, excluding the bloodline, was cut from five fish in each group, and 100g was used as one sample for gas chromatography analysis. As shown in Figure 3, the d-limonene content that supported the sensory evaluation results was confirmed in Examples 1 and 2.

Claims

1. A feed additive containing kabosu essential oil as an active ingredient, for imparting the aroma of kabosu to the meat of fish of the genus Yellowtail.

2. The feed additive for imparting the aroma of kabosu to the meat of yellowtail fish according to claim 1, wherein the kabosu essential oil is obtained by steam distillation using kabosu peel as a raw material.

3. A feed additive for imparting the aroma of kabosu to the meat of fish of the genus Yellowtail, as described in claim 1 or 2, used to prevent skin disorders in fish of the genus Yellowtail.

4. A feed additive for imparting the aroma of kabosu to the meat of yellowtail fish according to claim 1 or 2, wherein the limonene content is 55 to 94% by mass, the myrcene content is 5 to 30% by mass, and the γ-terpinene content is 1 to 10% by mass.

5. A feed for farming yellowtail fish containing kabosu essential oil.

6. The feed for farming yellowtail fish according to claim 5, comprising extruder pellets.

7. Feed for cultivating fish of the genus Yellowtail, according to claim 5 or 6, comprising 0.05% by mass or more and 0.30% by mass or less of kabosu essential oil.

8. The moisture content is 15.0% by mass or less, and the bulk density is 0.80 g / cm³. ３ 1.00g / cm or more ３ The following is a feed for farming fish of the genus Yellowtail, as described in claim 5 or 6.

9. A method for producing feed for farming yellowtail fish, comprising adding the fragrance-imparting feed additive described in claim 1 or 2 to a feed ingredient for farming.

10. Moisture content of 15.0% by mass or less, bulk density of 0.80 g / cm³ ３ 1.00g / cm or more ３ A method for producing feed for farming yellowtail fish according to claim 9, comprising adding the fragrance-imparting feed additive to the extruder pellets described below.

11. A method for producing farmed yellowtail genus fish that has been flavored with kabosu, comprising the step of feeding the fish with the aquaculture feed described in claim 5 or 6.

12. A method for cultivating fish of the genus Yellowtail, comprising the step of feeding the fish with the aquaculture feed described in claim 5 or 6.

13. A fish of the genus Yellowtail, obtained by the manufacturing method described in claim 11, which is imparted with the aroma of kabosu.

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