How to farm mackerel

Abstract

To improve the non-defective rate of pisciculture feed by improving the shape of the outer skin of pisciculture feed that has a double structure to reduce the risk of leakage of the liquid oil contained in an internal capsule from both ends of the pisciculture feed.SOLUTION: Provided is pisciculture feed for fishes belonging to Scombridae, comprising an outer skin forming the outer surface and an internal capsule wrapped by the outer skin, with its side surface showing a substantially cylindrical shape and both ends being covered and closed by the outer skin, while at least one of both ends having a tapered protrusion where the outer skin protrudes toward the end.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to fish feed for raising mackerel, and particularly to fish feed suitable for tuna farming. [Background technology]

[0002] In fish farming, a shift from live bait to compound feed is being promoted from the viewpoints of nutrition, stable supply, environmental pollution prevention, sustainable farming, etc., and various compound feeds have been developed. In particular, compound feeds tailored to the preferences of fish species have been proposed so that a shift to compound feed can be promoted for highly piscivorous fish species as well.

[0003] For example, Japanese Patent No. 5030043 and Japanese Patent No. 5615643 disclose fish feed having an outer layer and an inner layer. Japanese Patent No. 5030043 and Japanese Patent No. 5615643 state that these fish feeds are used for cultured fish such as tuna, which have high palatability, and that they have good feeding properties and feed efficiency. Japanese Patent No. 5926656 discloses a double-structure feed consisting of an outer skin and an inner shell containing a protein material and liquid oil, and states that this feed has high feeding properties and suppresses oil leakage. Furthermore, Japanese Patent No. 6106795 discloses a method for raising cultured tuna fish enriched in vitamin E by using such a double-structure feed. Summary of the Invention [Problem to be solved by the invention]

[0004] The double-structured feed of the above-mentioned prior art is molded using an encrusting machine, so it is unavoidable that the liquid oil (mainly fish oil) contained in the encrustation leaks out from the seams of the outer skin at both ends of the feed. In other words, the outer skin is inevitably thin at the seams, making it easy for the liquid oil to leak out from these areas.

[0005] An object of the present invention is to improve the shape of the outer shell to reduce the possibility of liquid oil leaking from both ends of the feed and thereby to increase the yield rate of the feed. [Means for solving the problem]

[0006] The present invention relates to feed for cultivating mackerel fish as described below in (1) to (6). (1) A fish feed for farming mackerel, characterized in that the side surface is roughly cylindrical due to an outer skin that forms an outer surface and an inner part that is wrapped around the outer skin, both ends are covered and closed by the outer skin, and at least one of the ends has a tapered protrusion formed by the outer skin protruding toward the end. (2) The feed for farming mackerel according to (1), wherein the thickness of the outer skin of the protruding portion increases in the direction of the end portion. (3) The feed for farming mackerel according to (1) or (2), characterized in that the protrusion is formed on both ends. (4) A fish feed for farming mackerel of any of (1) to (3), which has a reduced diameter portion whose diameter gradually decreases from the side surface toward the end portion with an outwardly convex curved surface, the protruding portion is formed at the end portion of the reduced diameter portion, and an inflection portion whose diameter gradually decreases with an outwardly concave curved surface toward the end portion is formed between the reduced diameter portion and the protruding portion. (5) The feed for farming mackerel fish according to any one of (1) to (4), wherein the protrusion has a trace of the outer skin constituting the outer surface narrowing toward the end. (6) The feed for cultivating mackerel family fish according to any one of (1) to (5), characterized in that the exoskeletons contain starch, protein and fish meal. (7) The feed for cultivating mackerel family fish according to any one of (1) to (6), characterized in that the mackerel family fish is a tuna. Effect of the Invention

[0007] According to the above-mentioned configuration of the present invention, the shape of the outer shell is improved, which reduces the leakage of liquid oil from both ends of the feed, and improves the quality rate of the feed. Also, the amount of feed consumed by farmed fish is increased. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a side view of fish feed for farming mackerel according to an embodiment of the present invention. [Diagram 2] 1 is a perspective view showing an end portion of fish feed for farming mackerel fish according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1 of the feed for farming mackerel according to an embodiment of the present invention. [Figure 4] FIG. 2 is a side view of fish feed in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] An embodiment of the present invention will be described with reference to the drawings.

[0010] <shape> Fig. 1 is a side view of fish feed 10 for farming mackerel fish according to an embodiment of the present invention. The fish feed 10 for farming mackerel fish according to this embodiment is composed of an outer skin 20 constituting the outer surface, and an inner shell 30 (see Fig. 3) that is wrapped around the outer skin 20. As shown in this figure, the fish feed 10 for farming mackerel fish has a side surface 11 that is approximately cylindrical.

[0011] Here, the term "approximately cylindrical shape" does not require that the shape of the side surface 11 be strictly cylindrical geometrically, but rather that it be sufficient if it is recognizable at a glance as being cylindrical or a similar shape. Therefore, it is acceptable for the cross section to be somewhat irregular or flattened, or for the cross section to be flattened due to its own weight or the overlapping of feed. The length and width of this approximately cylindrical shape can be adjusted as appropriate depending on the species and size of the mackerel fish to be fed.

[0012] Moreover, both ends 12 are covered and closed with the outer cover 20. At least one of the ends 12 has a tapered protrusion 15 formed by the outer cover 20 protruding toward the end 12. In this figure, the protrusion 15 is formed on both ends 12, but if at least one of the ends 12 has this protrusion 15, the possibility of liquid oil leaking therefrom is reduced. Of course, it is desirable that the protrusion 15 is formed on both ends 12 as shown in FIG. 1.

[0013] 1, the end 12 has a reduced diameter portion 13 having an outwardly convex curved surface from the side surface 11 toward the end 12, and the protruding portion 15 is formed at the end 12 of the reduced diameter portion 13. By having the outer shell 20 protrude as the protruding portion 15 at the end 12 in this manner, the end 12 is formed thicker than if the reduced diameter portion 13 were formed in a shape of the end 12 that simply extends with an outwardly convex curved surface, and thus liquid oil is less likely to leak out.

[0014] In addition, an inflection part 14 is formed between the reduced diameter part 13 and the protruding part 15, the diameter of which gradually decreases with an outwardly concave curved surface toward the end part 12. It is considered that the presence of this inflection part 14 makes the outer diameter more similar to that of small fish that serve as food, thereby increasing the palatability of the lure as food for mackerel fish.

[0015] As shown in the perspective view of FIG. 2, the protrusion 15 has a trace 21 where the outer skin 20 constituting the outer surface is narrowed toward the end 12. The trace 21 can be composed of, for example, a plurality of radial lines. These lines can be distinguished visually or by touch, and are also considered to promote feeding by mackerel fish. These lines are preferably configured as grooves that do not reach the inclusion 30. The trace 21 may also be formed by narrowing the outer skin 20 toward the axial center.

[0016] Furthermore, as shown in the cross-sectional view of Fig. 3 (cross-section III-III of Fig. 1), the outside of the fish feed 10 for mackerel is covered as a whole with an outer skin 20, and the inner shell 30 is wrapped in this outer skin. It is also recognized that the outer skin 20 protrudes with an increased thickness toward the end 12 at the protruding portion 15 of the end 12. Since the thickness of the outer skin 20 at the protruding portion 15 is thus greater than that of the side surface 11, the strength of the outer skin 20 at the end 12 is actually increased. This reduces the possibility of leakage of liquid oil contained in the inner shell 30 from the end 12.

[0017] It is desirable that the shape of the above-mentioned fish feed 10 for farming mackerel is maintained until it is finally fed to mackerel at the fish farm. However, as long as it has the above-mentioned shape when it is made into a molded product in the process described below, the shape may be deformed by crushing or removing the protruding part 15 before feeding.

[0018] <Outer skin> The outer skin 20 may contain one or both of starch and protein as its components. The outer skin 20 may also contain fish meal. In this embodiment, the outer skin 20 may be of any type as long as it contains the above-mentioned components and can encase the inclusion 30, but the physical properties of a gel formed by heating a protein or a gel formed by heating a starch are suitable for the outer skin 20 in terms of flexibility, extensibility, and the like. As the protein, a protein-containing substance having gel-forming ability, such as a simple substance such as fish meat, minced fish, krill, gluten, collagen, soy protein, enzymatically decomposed soy protein, gelatin, or egg white, or a mixture of two or more of these, is preferable. As the starch, tapioca starch, wheat starch, potato starch, corn starch, soybean starch, waxy corn starch, or processed starch thereof is preferable. Food materials containing a large amount of these proteins and starches can also be used. The outer layer of the composition containing these proteins and starch is fixed as a gel by heating, has flexibility, and has a certain strength because it can retain the inclusions 30. In addition to or in place of the above-mentioned components having the physical properties of a gel formed by heating protein or starch, a component that gels when heated and melted and then released heat or cooled can be used. Examples of such components include gelatin and agar.

[0019] When the main component of the outer skin 20 is protein, for example, when fish paste is used as the main component of the outer skin 20, it can be produced using a general method for producing fish cakes and other paste products. Specifically, 2% or more of salt is added, the mixture is left at 10°C or higher, preferably 30°C to 40°C, for 10 minutes or more, and then heated at 80°C to 90°C for 10 minutes or more. Alternatively, when egg white is used, a composition with desired physical properties can be obtained by mixing egg white, starch, fish meal, and water in ratios of 10% by weight, 10% by weight, 20% by weight, and 60% by weight, respectively, and heating the mixture.

[0020] In order to increase the nutritional efficiency of the fish feed 10 for farming mackerel fish, it is preferable that the feed as a whole has a low moisture content, high protein and high fat content as much as possible. Therefore, it is preferable to add fish meal and oil to the outer skin 20 as well to the extent that it does not affect the gelation of the outer skin 20. Although it depends on the type of gel used, it is possible to add up to 60% by weight of fish meal and up to 30% by weight of oil to the outer skin. It is preferable to add about 20 to 30% by weight of fish meal and 5 to 10% by weight of oil.

[0021] In order to improve the quality of the gel of the outer skin 20, additives used as quality improvers for fish paste products and the like can be added as appropriate. Specifically, in addition to the above-mentioned starch, thickening polysaccharides, isolated soy protein, sodium bicarbonate, polymerized phosphate, transglutaminase, various protease inhibitors, and the like may be added. In particular, in order to strengthen the gel strength, thickening agents such as agar, gellan gum, pullulan, mannan, carrageenan, xanthan gum, locust bean gum, curdlan, pectin, alginic acid and its salts, gum arabic, chitosan, dextrin, and edible water-soluble cellulose may be appropriately blended. However, since tuna and many other mackerel fish have a low digestive ability for polysaccharides, it is preferable to keep the polysaccharides to a minimum, and it is desirable to use a thickening agent in the material of the outer skin 20 of preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1.5% by weight.

[0022] As the outer skin 20 of this embodiment, a heated gel mainly composed of starch is also excellent in terms of its elasticity and flexibility. A gel obtained by adding water to starch, kneading it, and heating it has elasticity, flexibility, and extensibility. In particular, various processed starches each have their own characteristics, and by combining two or more types, an outer skin 20 having properties such as elasticity, flexibility, and extensibility can be obtained. For example, it is good to combine different types of processed starch, such as a combination of etherified starch and phosphate cross-linked starch. An even stronger gel can be obtained by adding a protein such as gluten or soy protein to such starch. Instead of gluten, wheat flour containing gluten can also be used. Other auxiliary ingredients may include cereal flour such as wheat flour, proteins such as soy protein, gluten, and egg white, sugars and sugar alcohols such as sugar and starch syrup, carrageenan, agar, gellan gum, pullulan, mannan, xanthan gum, locust bean gum, curdlan, pectin, thickeners such as alginic acid and its salts, gum arabic, chitosan, dextrin, and edible water-soluble cellulose, and salts such as phosphates. For example, adding wheat flour to starch can give strength to the outer skin 20. Also, adding a certain amount of protein can suppress the stickiness of the surface after heating.

[0023] The fish feed 10 for farmed mackerel of the present invention, which has an inner layer 30 mainly made of fish meal and fish oil wrapped in an outer layer 20 mainly made of heated starch gel, is favored by fish because the outer layer 20 is elastic and flexible. In terms of production efficiency, it has excellent extensibility properties and is suitable for wrapping the inner layer using an encrusting machine or extruder.

[0024] In this embodiment, the starch used as the main component of the outer shell 20 is not particularly limited, but tapioca starch, wheat starch, potato starch, corn starch, soybean starch, etc. can be used, and processed starches such as etherified, acetylated, acetyl-crosslinked, ether-crosslinked, phosphate-crosslinked, and alpha-hydroxypropyl phosphate-crosslinked starches are particularly preferred. Other auxiliary materials such as protein and fish meal are added to these starches, and water is added and mixed and kneaded to form the outer shell 20, which is then wrapped around the inner shell 30 using a stuffing machine or the like, and heated to produce the fish feed for farming mackerel fish 10 of this embodiment. Alternatively, the outer shell 20 raw material and the inner shell 30 raw material can be supplied to a double nozzle extruder, and the outer shell 20 raw material can be mixed and heated while simultaneously extruding the outer shell 20 to wrap the inner shell 30. The amount of water added to the raw material such as starch may be any amount that ensures a viscosity that can be used in an encrusting machine or extruder, and is preferably about 30 to 50% by weight. The heating temperature may be any temperature at which starch or added proteins gel, or higher, and may be such that the weight loss of the outer skin 20 is 60 to 120°C, preferably about 70 to 100°C. Since fish oil is easily oxidized, it is preferable to avoid high temperatures exceeding 120°C.

[0025] There are various possible patterns for the composition of the outer shell 20 containing starch. The nutrients and calories required for the feed vary depending on the species of fish to be cultivated and the growth stage of the fish. The more fish meal or fish oil is added, the more strictly the composition of the outer shell 20 needs to be prepared, but when the amount of fish meal or fish oil is less, the composition of the outer shell 20 has a considerable degree of freedom. It is desirable to have at least 20 to 80% by weight of starch in dry matter terms. When 25 to 50% by weight of fish meal is added to the outer shell 20 in dry matter terms, it is preferable to add 20 to 65% by weight of starch, 5 to 20% by weight of wheat flour, and about 5 to 15% by weight of protein, oils and fats, thickeners, salts, etc. in dry matter terms. It is preferable to add 1 to 5% by weight of fish oil, 1 to 2% by weight of phosphate, 1 to 5% by weight of protein, and 1 to 5% by weight of thickener.

[0026] When wheat flour is used as a secondary ingredient for the outer skin 20, strong wheat flour having a high gluten content is preferable, but weak wheat flour may also be used.

[0027] In order to improve the quality of the outer skin, additives that are usually used as quality improvers for starch foods can be added.

[0028] <Inclusion> The composition of the inner layer 30 is mainly composed of fish meal and oils and fats, but other nutritional components known as nutritional components for fish farming, such as vitamins and minerals, may be added. In addition, since it is undesirable for the fish meal and liquid oils wrapped in the outer skin 20 to leak, polysaccharides and hardened oils may be blended and emulsified for stabilization. In particular, when manufacturing by machine, it is preferable to make the physical properties of the inner layer composition fluid and physical properties suitable for machinery. In addition, it is preferable to add hardened oil that solidifies fish oil and porous materials that adsorb fish oil. Examples of polysaccharides as oil adsorbents include Oil Q (trade name, manufactured by Nihon Starch Chemical Co., Ltd.) and powdered soy protein New Fujipro SEH (trade name, manufactured by Fuji Oil Co., Ltd.).

[0029] Fish oil is liquid at room temperature, and when the temperature rises, the viscosity decreases and may seep out from the outer skin 20. In order to avoid this, it is preferable to mix hardened oil with the fish oil. Hardened oil is a white solid fat obtained by hydrogenating animal and vegetable oils such as fish oil, soybean oil, and rapeseed oil. Raw material oil contains unsaturated fatty acids such as oleic acid, linoleic acid, linolenic acid, and other highly unsaturated fatty acids as component fatty acids, but hydrogenated oil is a fat in which hydrogen is added to unsaturated fatty acids, reducing the amount of unsaturated fatty acids, and finally becoming saturated fatty acids and solid fats. By adding hardened oil, the liquid oil can be made into a paste or solid. In order to prevent the fish oil contained in the inclusion 30 from leaking or seeping out from the cracks and gaps in the outer skin 20 from the fish feed 10 for farming mackerel fish, it is preferable to add hardened oil having a melting point of 50°C or more. Such hardened oils are those in which the main fatty acid component constituting the hardened oil (the fatty acid with the highest amount in the fatty acid composition) is a fatty acid having 18 or more carbon atoms and the iodine value (the mass of iodine absorbed in 100 g of fats and oils (unit: g)) is 0 to 2. The iodine value of hardened oils sold as extremely hardened oils falls within this range. Examples of preferred hardened oils include lard extremely hardened oil (manufactured by Yokoseki Oil Industries Co., Ltd.), Unishort K (trade name, manufactured by Fuji Oil Co., Ltd.), High-Elsine rapeseed extremely hardened oil (trade name, manufactured by Yokoseki Oil Industries Co., Ltd.), beef tallow extremely hardened oil (manufactured by New Japan Chemical Co., Ltd.), soybean extremely hardened oil (manufactured by Yokoseki Oil Industries Co., Ltd.), rapeseed extremely hardened oil (manufactured by Yokoseki Oil Industries Co., Ltd.), and TAISET50 (trade name, manufactured by Taiyo Kagaku Co., Ltd.). In particular, highly hydrogenated high erucine rapeseed oil (trade name, manufactured by Yokozeki Yushi Kogyo Co., Ltd.), which contains a large amount of fatty acids having 20 or more carbon atoms, such as behenic acid having 22 carbon atoms, is preferred. The amount of hydrogenated oil added is preferably 0.5 to 15% by weight, particularly 1 to 10% by weight, based on the amount of liquid oil, such as fish oil, in the inner layer. Since the digestibility of hydrogenated oil by fish is not high, it is preferable to use an amount not exceeding 5% by weight based on the total weight of the feed. In addition, the addition of hydrogenated oil results in an inclusion 30 with a certain degree of viscosity, and therefore the mechanical suitability is also good when the inclusion 30 is wrapped in the outer skin 20 and molded.

[0030] Furthermore, raw materials used in conventional compound feed for farmed fish can be added to the composition of the inclusion 30. For example, raw fish, proteins such as squid meal, krill meal, soybean oil cake, and corn gluten meal, oils and fats such as krill oil, whale oil, soybean oil, corn oil, rapeseed oil, and hardened oil, starches such as starch, wheat flour, rice flour, tapioca flour, and corn flour, polysaccharides such as alginic acid and its salts, sodium carboxymethylcellulose (CMC), guar gum, dextrin, chitosan, curdlan, pectin, carrageenan, mannan, gellan gum, gum arabic, and edible water-soluble cellulose, vitamins, minerals, and the like.

[0031] The composition of the inclusion 30 is formulated so that the fat content is 20 to 70% by mass, and in particular, when feeding large farmed fish such as tuna, the fat content is preferably 30% by mass or more, more preferably 35% by mass or more, and most preferably 45% by mass or more. A large amount of fat content has an excellent effect on the growth and growth efficiency of farmed fish, but if the fat content exceeds 70% by mass, the other ingredients are inevitably reduced, making it difficult to adjust the nutritional balance. Fish oil and other vegetable oils and fats have high fluidity and may be used as they are, but preferably, dextran such as Vitacell WF200, Vitacell WF600 or Vitacell WF600 / 30 (all trade names, manufactured by Rettenmeyer), Oil Q No. 50 or Oil QS (all trade names, manufactured by Nippon Starch Chemical Co., Ltd.), Pine Flow (manufactured by Matsutani Chemical Industry Co., Ltd.) and other oil-absorbing polysaccharides, oil-absorbing proteins such as fermented soybeans and isoflavones, or hardened oils obtained by hydrogenating oils such as soybean oil, rapeseed oil or palm oil, may be used after reducing the fluidity. Alternatively, the fluidity of fish oil may be reduced by emulsifying it. However, considering the digestibility of fish, it is desirable that the amount of these components that reduce the fluidity is preferably 10% by mass or less, more preferably 5% by mass or less, of the composition of the inclusion 30. As the oil and fat, fish oil is most preferable, but it is also possible to partially replace it with other vegetable oils and fats.

[0032] The fish meal, which is an essential component of the inclusion 30, can be any of various fish meals commonly used as fish feed ingredients, krill or other crustacean powders, etc. The fish meal content is blended to be 30 to 70% by mass, preferably 30% by mass or more, more preferably 35% by mass or more, and most preferably 45% by mass or more.

[0033] <Mackerel family>

[0034] In view of the above-mentioned shape, the fish feed 10 for farming mackerel of this embodiment is a feed suitable for farmed mackerel, particularly tuna such as bluefin tuna (Thunnus orientalis, Thunnus thynnus), southern bluefin tuna (Thunnus maccoyii), yellowfin tuna (Thunnus albacares), and bigeye tuna (Thunnus obesus). EXAMPLES

[0035] <Manufacturing method for mackerel farming fish feed> The outer cover 20 had the composition shown in Table 1 below.

[0036] [Table 1]

[0037] The above composition was mixed in an extruder under conditions of a screw rotation speed of 450 rpm, a discharge temperature of 90° C., and an outlet pressure of 5 MPa to obtain a composition for skins.

[0038] The inclusion 30 had the composition shown in Table 2 below.

[0039] [Table 2]

[0040] The above composition was mixed at 60° C. using an extruder to form the inclusion 30. The vitamins used contained 3.03% by weight of vitamin E calculated as α-tocopherol.

[0041] In order to produce fish feed 10 for mackerel using the above-mentioned outer skin composition and the above-mentioned inclusion 30, a co-rotating, fully intermeshing, twin-screw extruder (manufactured by Buhler) with a double nozzle at the tip and an extrusion capacity of 1 t / h was used.

[0042] Both the composition for the outer shell and the inclusion 30 were granulated from a double nozzle at the tip of an extruder, and a molded product in which the inclusion 30 was covered with the outer shell 20 was obtained as fish feed 10 for mackerel by a shutter device. The weight ratio of inclusion to outer shell was 7:3. The α-tocopherol content in the fish feed 10 for mackerel was 621 ppm.

[0043] Thereafter, the feed immediately after molding was placed on a transport conveyor and dried naturally for 24 hours in an environment of 30°C to 40°C and a relative humidity of 20% to 50%. This treatment resulted in a good mixed feed with almost no cracks or the like on the surface, including both ends 12.

[0044] The moisture content of the outer skin 20 of the obtained mackerel fish feed 10 was 12 to 17%, and the water activity was less than 0.8. The moisture content of the inclusion 30 was estimated to be about 4.7% immediately after molding. The moisture content was measured using a Drying Oven DX300 (manufactured by Yamato Scientific Co., Ltd.), and the water activity was measured using an Aqua Love CX-3 (manufactured by Milestone General Co., Ltd.).

[0045] The size of the mackerel fish feed 10 was, on average, 95 mm in total length between the bent parts 14 at both ends, 2.6 mm in length of the protruding part 15 from the bent part 14, and 38 g in weight.

[0046] As a comparative example, a fish feed 50 having no protrusions at both ends 52 as shown in FIG. 4 was also produced using the same composition and production process as the above-mentioned skin-element organisms and the above-mentioned inclusion 30.

[0047] <Testing the rate of acceptable products> After production and the above-mentioned drying treatment, the rate of non-defective products in which no leakage of liquid oil was observed from the ends 12, 52 was 65% in the comparative example, whereas it was 100% in the example.

[0048] As a durability test, the molded product was bent after molding with the shutter device, and the presence or absence of accompanying cracks at both ends 12, 52 and leakage of the encapsulation 30 was confirmed. Molded products that did not show any cracks at both ends 12, 52 or leakage of the encapsulation 30 even after such bending were determined to be good products, and the ratio of good products to the 100 molded products subjected to the durability test was determined to be the good product rate.

[0049] The yield rate in the durability test was 35% in the comparative example, whereas it was 100% in the example. From the above, it was found that the yield rate of the mackerel farming fish feed 10 was significantly improved by providing the protruding portion 15.

[0050] <Feeding test> In a farming cage housing 2,000 10 kg bluefin tuna, the comparative fish feed 50 was fed until the 42nd day, starting from the 0th day of feeding, and then the mackerel fish feed 10 of the embodiment was fed from the 43rd day, and the change in the amount of food intake was observed. The feeding method was so-called satiation feeding, in which the tuna were fed as much as they could eat. The results are shown in Table 3 below.

[0051] [Table 3]

[0052] As shown in Table 3 above, the average feed intake was 710 kg (355 g per fish) up to the 42nd day when the fish feed 50 of the comparative example was fed, whereas the average feed intake was 990 kg (495 g per fish) from the 43rd day onwards when the fish feed 10 of the mackerel family was fed, showing a clear increase. From this, it is considered that the protrusion 15 on the end 12 of the fish feed 10 of the mackerel family in the embodiment increased the feed intake. This is presumably because the shape of the fish feed is closer to the spindle shape of small fish such as sardines that tuna like.

Claims

1. The outer surface is formed of an outer skin having a moisture content of 12 to 17%, and the inner part is wrapped in the outer skin and has an oil content of 20 to 70% by mass, so that the side surface is generally cylindrical, both ends are covered and closed with the outer skin, and at least one of the ends is formed with a tapered protrusion in which the outer skin protrudes toward the end, The protruding portion has a trace of the outer skin constituting the outer surface being reduced in diameter toward the end portion, The trace is composed of a plurality of radial lines; A method for raising mackerel, comprising feeding mackerel feed, the outer skin of which contains starch, protein and fish meal, to cultured mackerel.

2. 2. The method for rearing mackerel fish according to claim 1, wherein the thickness of the outer skin of the protruding portion increases in the direction of the end portion.

3. 3. The method for raising mackerel fish according to claim 1 or 2, wherein the protrusion is formed on both ends.

4. a reduced diameter portion having a diameter gradually decreasing from the side surface toward the end portion along an outwardly convex curved surface, The protrusion is formed at the end of the reduced diameter portion, The method for rearing mackerel fish according to any one of claims 1 to 3, wherein an inflection portion having a diameter gradually decreasing with an outwardly concave curved surface toward the end portion is formed between the reduced diameter portion and the protruding portion.

5. 5. The method for raising mackerel fish according to claim 1, wherein the mackerel fish is a tuna fish.

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