AU2006216144B2 - Solid feed for large-sized fishes - Google Patents

Description

1 DESCRIPTION Solid Feed for Large-sized Fish Technical Field 5 This invention relates to cultivation technology of fishes. More specifically, it relates to solid feed for large-sized fishes. Background Art As the first shipment of completely cultured tunafish by 10 Fisheries Research Institute of Kinki University on September 3, 2004 attracted the public eye, further development in cultivation technology of still larger sized fishes than sea bream, flatfish, yellowtail and the like is much waited for. In the art of feed for fish culture which supports a part of cultivation technology, artificial 15 formula feed such as moist pellets (MP) or extruder pellets (EP) to partially or totally substitute live feed such as sardines for sea breams or young yellowtails have been developed. Whereas, while perishable or frozen sand eel lances, anchovies, Japanese pilchard [Sardinops melanostictus], horse mackerel 20 [Scomber japonicus], chub mackerel and cuttlefishes are used to feed larger-sized fishes represented by bluefin tuna [Thunnus orientalis], in accordance with the latter's growth stage, chub mackerel has been mostly used from the standpoints of the feed size, economy and nutrition. In respect of shaped formula feed, it is difficult to enlarge 25 the feed size when the MP- or EP-preparation methods only are relied on, because of the various factors constituting those methods. It is also difficult to provide the feed having adequate strength, while meeting the nutritive requirements and absorption-excretion level suitable for cultured fishes. 30 Heretofore proposed means aiming at larger-sized formula feed include mutual caking of plural grains of conventional type EP pellets (solid feed) molded with an extruder with, for example, modified dextrin and starch, or filling the plural grains in sheep casing or artificial casing like those used for hams or sausages to realize the 35 larger sizes (cf. Patent Reference 1, as in the later listed cited 2 literature references). It was suggested that the caked larger-sized feed quickened the digestion rate in the stomach of rainbow trout' [Oncorhynchus mykiss], as compared with conventional EP feed. There has been also provided a larger-sized solid feed for fish culture, which is prepared by extruding starting materials through twin-screw extruder into 5 columnar form and bundling and bonding three or more of the columns each and which therefore has voids in longitudinal direction (e.g., 25 - 50 mm in diameter and 35 - 100 mm in length) (cf. Patent Reference 2). These solid feeds for fish culture are characterized by quick drying, good shape retention during extrusion or drying, and high liking by yellowtail. 10 On the other hand, as an interesting structure of the solid feed while it is yet unknown whether suitable or not for size enlargement, columnar or encapsulated feed have been provided, which contain at their center part a heat-instable, essential ingredients for cultured fishes such as vaccine or medicine, as prepared with a double-nozzle extruder (cf. Patent Reference 3). As the claimed effect of such a feed, "it can provide special feed 15 to enable sure administration of vaccines or medicines to cultured fishes in the form of oral administration". Also a fishing bait having a lugworm-like structure is provided, which is characterized by using, as a substitute for lugworm or the like, two kinds of hard and soft starting materials of different composition for bait comprising fish paste, shaping them by filling tubes of the hard starting composition with the soft starting composition, 20 cutting the tubes to a suitable length and heating the same (cf. Patent Reference 4). Throughout the description and claims of the specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps. A reference herein to a patent document or other matter which is given as prior art 25 is not to be taken as an admission or a suggestion that that document or matter was, known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims. Disclosure of the Invention As above, wide varieties of solid feeds have been proposed but we do not know of 30 any artificial solid feed which is successfully used for cultivating tuna. Of the above-cited patent references, Patent Reference 1 is the latest disclosed and the solid feed described therein is suggested to show a quickened digestion rate in rainbow trout's stomach and easy decomposition in the digestive tract. According to our experiences, however, easy digestion or decomposition of solid feed 3 in the stomach occasionally invite excretion of undigested matter containing nutritious component. Therefore, provision of solid feed, which rather retains its original shape for a prescribed time in the stomach and stays for a 5 prolonged time in the stomach and intestines, is in demand. Furthermore, it is also desirable to provide solid feeds of versatile sizes or shapes, using a wide variety of starting materials at cheaper cost and by simple method. Surprisingly, we have discovered that the above demand or 10 need could be met by "core-shell" type solid feed having a structure that the cross section cut along its axial line (or along its longitudinal direction) is oval or approximately rectangular, which is formed of a shell having an external shape such as of a cylinder, rectangular parallelepiped, flattened cylinder (as transformed by pressing down a 15 cylinder in the direction of its shorter axis) or daifukumochi (a rice cake stuffed with bean jam), bean-jam bun, a cream puff, banana or migratory fish (e.g., anchovy, mackerel, horse mackerel, Pacific saury) and a core, with diverted use of bean-jam stuffer or encrusting machine [commonly referred to as a maniu (a bun with a bean-jam 20 filling) maker] or an apparatus having equivalent function to bean-jam stuffer, using each of prescribed certain starting materials for the crust (shell) and the content (core). It is also found, while the solid feeds are scheduled to be heat-dried in Patent References 1 and 2, that the solid feeds according to the present invention do not 25 require heat-drying but are suitable for feeding retaining their frozen condition, and furthermore can improve feed utilization effect. Still in addition, we have discovered that the solid feeds according to the invention exhibit further increased physical strength compared to those before freezing, when thawed after freezing and then air-dried 30 where necessary. The present invention is completed based on the foregoing discoveries. Accordingly, therefore, the present invention provides a core-shell type solid feed for large-sized fishes, which comprises (i) a 35 shell composed of an agglutinant substance containing nutrient for a 4 fish feed, and (ii) a core which is itself a fish feed or a composition containing nutritious component of a fish feed, and the shape of the solid feed corresponds to substantially rectangular parallelpiped or substantially flattened rectangular or substantially flattened cylindrical. 5 The invention also provides the solid feed in frozen state, and furthermore the solid feed once frozen and thereafter air-dried where necessary. As a method for preparing the above solid feed for large-sized fishes with high efficiency, the invention provides a process which comprises: (a) a step for formulating a crust material (shell-forming material) by mixing 10 and grinding nutrient for fish feed with an agglutant substance, adding water to the dough and kneading, (b) a step for preparing a filling material (core-forming material) by using a fish feed itself or a composition containing nutritious component of the fish feed, the composition being added with water and kneaded where necessary, 15 (c) a step for supplying a rod-like feed dough having a double structure of the crust material and filling material as obtained in the steps (a) and (b), to the opening of a crust-cutting apparatus capable of cutting the crust plural times, (d) a step of cutting the crust of the rod-like feed dough at a suitable length, (e) an optional step of further adjusting the crust-cut pieces as obtained in the 20 step (d) into a suitable shape and freezing them, and (f) an optional step of thawing the frozen solids. Brief Explanation of the Drawings Fig. I are the photographs given in place of drawings showing the appearance and 25 the section along the axial line (longitudinal axis) [(a) and (b), respectively] of the solid feed which was prepared in Production Example 3. Fig. 2 are the photographs given in place of drawings showing the content in the stomach of anchovy-fed fish and that in the stomach of the core-shell type pellet-fed fish [(a) and (b), respectively] as in the Feed Example. 30 5 Fig. 3 are the photographs given in place of drawings showing the shape of the rectangular parallelepiped core-shell type pellet. Photograph a shows the appearance, and photographs b and c, the sections cut along the long and short axes, respectively. 5 Detailed Description of the Invention The large-sized fishes said in the invention means mainly tuna represented by bluefin tuna, yellowfin tuna [Thunnus albacares, bigeye tuna [Thunnus obesus], albacore tuna [Thunnus alalungal, 10 southern bluefin tuna [Thunnus maccoyiil, longtail tuna [Tunnus tonggol] and blackfin tuna [Thunnus atlanticus], adult yellowtails and adult salmons. According to the present invention, size of the solid feed is freely adjustable and, therefore, size of the large-sized fishes is not limited. In general terms, however, fishes of the total 15 length not less than about 25 cm and body weight not less than about 300 g, preferably not less than 1000 g, more specifically those of at least the sizes equivalent to young bluefin tuna (yokowa), adult yellowtails and adult solmons can be the object to be fed. The breeding or culture of the object fishes is not limited to those aiming 20 at their growth, but include broadly those aiming at improvement in the quality of fish meat. Because the shell according to the invention is composed of an agglutinant substance containing nutrients for fish feed, the shape of the core-shell structure can be fed unbroken, and furthermore the 25 core can be selected from a wide variety of substances. Also because the shell contains nutrient(s) for fish feed, the feed can be made more agreeable with fishes. While the kind of agglutinant substance is not critical so long as it exhibits such actions and effects, it can be any one or mixture of at least two which are selected from the group consisting 30 of a-starch, -starch, wheat gluten, guar gum, carboxymethyl cellulose, gelatin, collagen, carrageenan, sodium alginate, agar and xanthane gum. Of these, particularly the use of at least a-starch enables to enhance strength of the resulting solid feed, and to control decomposition of the solid feed in the stomach, for example, according 35 to the use rate of a-starch, whereby to increase the enteral nutrient 6 absorption. As the starting starch for a-starch, for example, potato starch, corn starch, tapioca starch and the like can be named, but starch of any origin can be used. Any nutrients for fish feed can be used so long as they can 5 make the solid feed more agreeable with fishes, do not exceedingly reduce the structural strength of the shell, and can be homogeneously dispersed in the shell layer containing the agglutinant substance. Examples of such nutrient substances include, although not limited thereto, fish powder, krill meal, cuttlefish meal, ground fish meat, 10 animal meat powder of pig, chicken or the like, powdered bones of pig, chicken or the like, powdered animal matters such as feather meal, powdered blood and the like; grain flour such as wheat flour, rye flour, barley flour and the like; vegetable oil cake such as soybean cake, corn gluten meal, rapeseed oil cake and the like; powdered pulse such as 15 powdered soybean, powdered adzuki-bean and the like; chaff and bran such as de-fatted rice bran, rice bran and the like; brewage cake such as beer cake, cake of low-class distilled spirits and the like; yeast such as beer yeast, torula yeast and the like; oil and fat such as fish oil, soybean oil, corn oil, palm oil, rape oil and the like; minced meat of 20 fishes and shellfishes such as of sardine, mackeredl, saurel, saury or krill and the like; and powdered assorted feed for fisheries use which are commonly referred to as mash. Also blends of at least two of these nutrient substances are included in the nutrient substances useful for the invention. 25 The use rate of the agglutinant substance for fish feed cannot be specified because the optimum value changes according to individual combinations of the nutrient substance and the agglutinant substance. In general terms, however, it can be so selected as to provide at least 5 wt%, preferably at least 10 wt%, inter 30 alia, at least 15 wt%. Where 100 wt% - 5 wt% of the agglutinant substance is a-starch, the resulting solid feed can be given enhanced strength, controlled decomposition rate in the stomach and increased enteral absorption of the nutrient as earlier stated. Fish bait per se or compositions containing the former's 35 nutritious component which constitute the core can be of any starting 7 material so long as they have no detrimental effect on the strength of above-described shell structure and are useful for breeding or cultivation of large-sized fishes. Convenient examples of the starting material include, although not limited thereto, fish powder, krill meal, 5 cuttlefish meal, ground fish meat, animal meat powder of pig, chicken or the like, powdered bones of pig, chicken or the like, powdered animal matter such as feather meal, powdered blood and the like; grain flour such as wheat flour, rye flour, barley flour and the like; vegetable oil cake such as soybean cake, corn gluten meal, rapeseed 10 cake and the like; powdered pulse such as powdered soybean, powdered adzuki-bean and the like; chaff and bran such as de-fatted rice bran, rice bran and the like; brewage cake such as beer cake, cake of low-class distilled spirits and the like; yeast such as beer yeast, torula yeast and the like; oil and fat such as fish oil, soybean oil, corn 15 oil, palm oil, rapeseed oil and the like; minced or cut pieces of fishes and shellfishes such as of a sardine, mackerel, saurel, saury, cuttlefish or krill and the like; powdered assorted feed for fisheries use which are commonly referred to mash, perishable fishes and shellfishes such as sardine, mackerel, saurel, saury, cuttlefish, short-necked clam or 20 krill and the like; frozen fishes and shellfishes such as a sardine, mackerel, saurel, saury, cuttlefish, short-necked clam or krill and the like; and assorted feeds for fishes. Also blends of two or more of these fish feeds themselves or compositions containing their nutritious components are included in those compositions. In this 25 specification, sardine, mackerel and saurel are generic names. For example, "sardine" is to cover a general idea including Japanese sand lance, anchovy, Japanese pilchard and the like. As the above enumerated nutritious components or compositions themselves or as their starting materials, almost all of 30 those available on the market can be used as they are or with minor modification. Starting materials of the core can contain a large amount of oil or fat, typically fish oil and animal fat. For example, an assorted feed for fishes which is made a flowable paste by addition of fish oil 35 can be used as a core. A core can contain up to 40 wt%, preferably up 8 to 35 wt%, of oil, based on the total weight of the core material. The core or shell may contain those customarily used as additives for feed, for example, vitamins such as vitamin B 1 , vitamin E, vitamin C; minerals such as zinc sulfate, copper sulfate, magnesium sulfate; 5 digestive enzymes such as protease, amylase, lipase; living bacteria such as lactic bacteria; coloring matter; and the like. The core-shell type solid feed having the described composition is size-free as aforesaid, but we intend to provide the feed corresponding to spheres of at least 2 cm, preferably at least 5 cm, in 10 diameter, when converted to a spherical shape. Moreover, we do intend to provide cigar- or banana-shaped feed with 1 - 7 cm, preferably 2 - 5 cm in diameter of the cross-section and 6 - 30 cm, preferably 10 - 20 cm in longitudinal length. Again, when the feed is substantially rectangular parallelepiped, it can be 1 - 3 cm high, 2 - 6 15 cm wide and 3 - 20 cm long. "Substantially rectangular parallelepiped" means that the parts corresponding to each side may be rounded. Whereas, the solid feed according to the present invention can have any shape and size, which can be suitably selected according to such factors as the species and size of the fish to be 20 cultivated. Particularly because the solid feed of the invention can be manufactured with diverted use of an encrusting machine or an apparatus having equivalent function thereto, solid feed of various shapes can be offered, for example, those having a cylindrical or rectangular parallelepiped external form with oval or rectangular 25 section when cut at right angle with its axial line (or right angle with longitudinal axis), or flattened cylindrical shape (cylinder which is deformed by compression in the direction of its shorter axis), for example, those having cigar-like, banana-like spherical or bowl-like appearance, or those of a shape resembling migratory fish (e.g., an 3o anchovy, mackerel, saurel, saury and the like). Because shape of solid feed can affect feed intake in concert with feeding environment (e.g., water temperature variation, dissolved oxygen level, turbidity at surface of the sea, salt concentration, presence of ocean current, and the like), the optimum shape cannot be specified. In general terms, 35 flat shape and approximate rectangular parallelepiped are preferred, 9 flat shape being particularly preferred. From the standpoints of strength of the solid feed and its adequate residence time in fish's digestive organ, the average thickness of the shell portion in the core-shell structure can generally 5 be 5% - 95% , preferably 10% - 40%, inter alia, 10% - 30%, of the sectional area of the solid feed. Again, when expressed by weight % of the shell portion per the total weight of the core-shell, the shell portion can generally occupy 5% - 90%, preferably 10% - 75%, inter alia, 10% - 50%, while it changes more or less depending on specific 10 gravity values of individual starting materials. In the above, average thickness of the shell portion is referred to, it being preferred that the shell portion in the solid feed has a uniform thickness. Minor extent of variation, however, is allowable so long as the object of the present invention is achieved. It is also desirable that 15 substantially the whole of the core surface is covered with the shell. That "substantially the whole is covered with the shell" signifies the state that at least 90%, preferably at least 95%, inter alia, 100%, of the core surface is covered. Preferably, structure of the shell portion is so selected that the 20 solid feed will have the strength to enable its efficient feeding over a great distance with a pellet feeder without damage on its shape, for example, to a place distant by 5 meters or more, through a carrier pipe connected to a pressurized air blower, at a suitable angle. As a typical pellet feeder for such use, Air Feeding Machine JMM-100ES 25 manufactured by Furuta Electric Co., Ltd. can be named. According to the present invention frozen solid feed is also provided, and it is not always required to efficiently feed it in unfrozen state to a remote place with a pellet feeder. However, when ease of handling is considered, the shell of above-described 30 construction is preferred. When the solid feed having so constructed shell is frozen, thawed and air-dried, its strength can be improved over that of the solid feed before the freezing, although the mechanism of such improvement is not yet clarified. While the solid feed in which at least 50%, preferably at least 80%, of the shell is 35 frozen falls within the scope of "frozen solid feed" as referred to in the 10 present invention, preferably the shell portion should be 100% frozen. Although not theoretically binding, in such frozen solid feed according to the present invention, infiltration of the oil component or the like of the core into the shell is prevented probably because the shell is 5 frozen, which results in better shape retention of the shell than the case of leaving unfrozen solid feed left standing at ambient temperature. Thus the solid feed's stability in water can be further improved, in other words, the solid feed can be made more resistant to decomposition or dissolution. 10 The solid feed as described in the above can be efficiently manufactured by the diverted use of an encrusting machine or an apparatus having the function equivalent thereto, the process being offered as another embodiment of the present invention. As such an apparatus, for example KASEIJINTM manufactured by Rheon 15 Automatic Machinery Co., Ltd. can be named. A convenient production process of the solid feed is explained hereinbelow, although not in the limitative sense. (i) Preparation step of the shell material Any device or method may be used in the preparation step of 20 the shell material, so long as the individual starting ingredients of the shell can be mixed well. For example, pasty eel feed making machines (e.g., Paste Making Machine manufactured by Nishimura Seiki Industries Co., Ltd.) can be conveniently used. An agglutinant substance and nutritious component(s) for fish feed are put in a pasty 25 eel feed making machine, mixed thoroughly to form a homogeneous mixture of the agglutinant substance and nutritious component(s). Water is added to the mixture, where necessary, to give an adequate viscosity for the shell. In this step the agglutinant substance and nutritious component(s) may be pre-mixed in advance to improve 30 homogeneity of the mixture, with a mixer (e.g., V-shaped mixer SVM Model by K.K. Seishin Kigyo, V-MIXER VM-30 Model by Fuji Paudal Co., Ltd. or the like). (ii) Preparation step of the core material Any device or method may be used in the preparation step of 35 the core material, so long as all the starting materials for the core can 11 be mixed well. For example, moist pellet granulating machines (SH5001 Model by Furuta Electric Co., Ltd., MGM 2000 KT by K.K. Sanko Techno Co., Ltd. or the like) can be used conveniently. Into a mixing tank of such a moist pellet granulating machine, a fish feed 5 itself or a composition containing the former's nutritious component(s) is thrown and thoroughly mixed. Thereafter the mixture is extruded through the moist pellet granulating machine to serve as the core. (iii) Shaping step of the core-shell type pellets 10 While any device or method may be used in the shaping step of the core-shell type pellets, so long as the core material can be wrapped in the shell material, use of encrusting machine (KASEIJINTM CN 500 by Rheon Automatic Machinery Co., Ltd. or ROBOSEVEN AR 800 by KOBIRD Co., Ltd. and the like) is convenient. Into the hopper for 15 outer crust material, which is located at an upper part of such an encrusting machine, the shell material as prepared in the above is thrown and into the hopper for filling, the core material as prepared in the above is thrown, respectively, and the core-shell type pellets of optional size and shape can be prepared by adjusting rpm of the 20 carrier motors for the crust material and the filling, nozzle-ring size and operational interval of the cutter. Thus obtained shaped product may further be pressed in a specific direction where necessary, to provide a deformed shaped product. (iv) Refrigeration or freezing step 25 While any device or method may be used in the freezing step so long as mutual caking and blocking of the core-shell type pellets can be prevented, it is convenient to use a tunnel freezer which excels in freezing efficiency. The tunnel freezer is normally operated at -10*C - -35 0 C. The lower the temperature, the shorter can be the freezing 30 time and the more advantageous, while any freezing temperature which does not bring about blocking of the core-shell type pellets as aforesaid can be used. Thus prepared frozen solid feed can be fed to fishes, as thawed, where necessary. Any method or device can be used for the thawing, so long as it does not induce decomposition of 35 the core-shell type pellets and deterioration of their components.

12 Thawed or defrozen solid feed of the present invention can be obtained normally by allowing the frozen feed to stand in a room at ambient temperature or cooled to around -5 0 C, under ventilation where necessary. 5 Hereinafter the invention is explained more specifically, referring to specific examples. Production Example 1 (1) Preparation step of shell material 10 A mixture of fish powder, a-starch, vitamin mix and mineral mix, which had been mixed in advance with a mixer (V-MIXER VM-30 Model by Fuji Paudal Co., Ltd.), fish oil and water were charged in an pasty eel feed making machine (Paste Making Machine by Nishimura Seiki Industries Co., Ltd.: processing capacity, about 10 kg/batch) and 15 mixed thoroughly to homogeneity to provide a shell material. The blend ratios of individual components in the shell material were as in the following Table 1. TABLE 1 20 Blend Ratio of Individual Components of the Shell Material Starting material Blend ratio Fish powder 45.6% a-Starch 6.1% Vitamin mix 0.4% Mineral mix 0.6% Fish oil 5.2% Water 42.1% Total 100.0% (2) Preparation step of core material Into the mixing tank of a moist pellet granulation machine 25 (MGM2000KT by K.K. Sanko Techno Co., Ltd.), HAMAKAZE STTM, an assorted feed for red sea bream (Chrysophrys major), by Mercian 13 Corporation, fish oil and chopped frozen anchovies were thrown, mixed thoroughly and extruded through the moist pellet granulating machine. The extrudate was used as the core material. The blend ratio of the core material was as in the following Table 2. The feed 5 additives contained in HAMAKAZE ST and their blend ratios were as shown in Table 3, and the blend ratios of the nutrients were as in Table 4. TABLE 2 Blend Ratios in the Core Material 10 Starting Material Blend Ratio HAMAKAZE ST 54.5% Frozen anchovy 39.7% Fish oil 5.8% Total 100.0% TABLE 3 Feed Additives Used in HAMAKAZE ST and Their Blend Ratios Feed additives contained: 15 vitamin A, vitamin D 3 , vitamin E, vitamin C, nicotinic acid, pantothenic acid, inositol, vitamin B 2 , vitamin B 1 , folic acid, vitamin B12, biotin, vitamin K3, iron sulfate, binding agent (sodium carboxymethyl cellulose), ethoxyquin. Starting materials: 20 Classified Starting Blend Ratio Starting Material Material (%) Animal feed 49.5 fish oil Chaff and bran 20.7 defatted cake defatted soybean oil cake, corn Vegetable oil cake 20.0 gluten meal Grain 5.6 wheat flour (off grade) Others 4.2 guar gum, calcium phosphate 14 TABLE 4 Nutrients in HAMAKAZE ST Nutrient Amount (wt%) Crude protein at least 44.0% Crude fat at least 4.5% Crude fiber at least 5.0% Crude ash content at least 15.0% Calcium at least 1.5% Phosphorus at least 1.5% 5 (3) Shaping step of core-shell type pellets The shell material was thrown into the crust hopper at an upper part of an encrusting machine (KASEIJIN CN500, Rheon Automatic Machinery Co., Ltd.) and the core material, into the hopper for the filling to be encrusted of the same machine. The rotation 10 numbers of the motors for carrying the crust and the filling were each set at 36.5 (the scales on the encrusting machine), the nozzle, at 12 mm, the ring, at 20 mm, and the working interval of the cutter, at once/second, to make cylindrical core-shell type pellets each 20 mm in the shorter diameter and 60 mm in longer diameter. The thickness 15 of the shell portion therein was 20% on the average. (4) Freezing step of the core-shell type pellets The shaped core-shell type pellets were directly frozen using a tunnel freezer, at -35*C and contact time (passing time) of 15-minutes. 20 Production Example 2 The operations of Production Example 1 were repeated except that the operation mode of the encrusting machine in the Production Example 1 was changed as follows: the rotation numbers of the 25 motors for carrying the crust and the filling, respectively to 76.2 and 99.5 (the scales on the encrusting machine), the nozzle, to 36 mm, and the ring, to 42 mm. Core-shell type pellets each 42 mm in the 15 shorter diameter and 100 mm in longer diameter were obtained. Production Example 3 The operations of Production Example 1 were repeated except 5 that the operation mode of the encrusting machine in the Production Example 1 was changed as follows: the rotation numbers of the motors for carrying the crust and the filling, to 76.2 and 99.5, respectively (the scales on the encrusting machine), the nozzle, to 36 mm; the ring, to 48 mm, and the working interval of the cutter, once/2 10 seconds. Core-shell type pellets each 50 mm in the shorter diameter and 120 mm in longer diameter were obtained. Photographs of the solid feed as obtained are shown as Fig. 1, instead of its drawings. In the figure, (a) shows the appearance and (b), a sectional view cut along the long axial line. 15 Production Example 4 Preparation of the solid feeds at varied use ratios of the core material and shell material (1) Preparation of the shell material 20 A mixture of fish powder, a-starch, vitamin mix and mineral mix, which had been mixed in advance with a mixer (V-MIXER VM-30 Model, Fuji Paudal Co., Ltd.), fish oil and water were fed into an eel paste feed-making machine (NERIEKI, Nishimura Seiki Industries Co., Ltd.) and mixed thoroughly to homogeneity, to serve as the shell 25 material. The blend ratio of the components were the same to Table 1 in Production Example 1. (2) Preparation of the core material Into the mixing tank of a moist pellet granulating machine 30 (MGM 2000 KT, Sanko Techno Co., Ltd.), a mixture of fish powder, wheat flour (off grade), soybean oil cake, vitamin mix and mineral mix, which was made at Yashiro Feed Manufactory of Mercian Corporation, chopped frozen anchovy and water were fed, mixed and extruded through the granulating machine to provide the core material. The 35 blend ratios in the core material were as in the following Table 5.

16 TABLE 5 Blend Ratios in the Core Material Starting Material Blend Ratio Fish powder 30.0% Wheat flour (off grade) 11.0% Soybean oil cake 12.0% Vitamin mix 1.0% Mineral mix 1.0% Chopped frozen fish 35.0% Water 10.0% Total 100.0% 5 The shell material was thrown into the crust hopper of an encrusting machine (KASEIJIN CN500, Rheon Automatic Machinery Co., Ltd.) and the core material, into the filling hopper, respectively, and the core-shell type solid feeds were prepared under the conditions as specified in Production Example 1 and as would give the thickness 10 ratios as in the following Table 6 (corresponding weight ratios). TABLE 6 Thickness Ratio Shell Core 5% 95% 10% 90% 15% 85% 20% 80% 25% 75% 30% 70% 35% 65% 40% 60% 45% 55% 50% 50% 55% 45% 60% 40% 70% 30% 75% 25% 80% 20% 17 Weight Ratio Shell Core 13.36% 86.64% 25.62% 74.38% 36.80% 63.20% 46.90% 53.10% 55.95% 44.05% 63.97% 36.03% 71.00% 29.00% 77.08% 22.92% 82.28% 17.72% 86.64% 13.36% 90.24% 9.76% 93.13% 6.87% 97.09% 2.91% 98.32% 1.68% 99.14% 0.86% The specific gravity values of the shell material and core material were 1.04 and 1.12, respectively. None of the solid feeds of the given ratios in Table 6 5 decomposed when fed with later described Air Pellet Feeder JMM-100ES. From the standpoint of nutritive value of cultivated fish, those having the shell ratio (thickness) of 5% - 30% are preferred. 10 Feed Example 1 (1) Feeding One-hundred and fifty (150) bluefin tunas (Thunnus orientalis) per group of 2.3 kg in body weight on the average, which had been cultivated on frozen anchovy [Engraulis japonica], Japanese sand 15 lance and the like, were kept in net cages [each 12 m X 12 m X 10 m (depth)] and fed for 7 days to satiation with frozen anchovies or the core-shell type pellets as obtained in Production Example 1, respectively, to accustom the fish to the taste of the respective feeds. The composition of each of the feeds was as given in Table 7. The 20 average amount per day of the fed anchovies during the 7 days was 45 kg. Then the fish were fasted for 2 days. On the day next, 45 kg of frozen anchovies, and 20.4 kg of the core-shell type pellets which was 18 equivalent in dry weight to that of the anchovies from which the water content was excluded, were fed to the respective groups of the fish. It was visually confirmed that both feeds were completely eaten. The water temperature at the feeding time was 17.5*C. 5 Both the frozen anchovies and the core-shell type pellets were fed by throwing them to the center parts of the net cages with Air Pellet Feeder JMM-100ES made by Furuta Electric Co., Ltd. The core-shell type pellets did not crumble in the occasion of feeding. The componential analysis of the frozen anchovies and the 10 core-shell type pellets was conducted following "Standard Feed Analysis" (Notification from Director of Animal Industry Office, The Ministry of Agriculture and Forestry, 7- Chiku B No. 1660, November 15, 1995). 15 TABLE 7 Composition of Given Feeds Component Anchovy Core-shell Type Pellet Crude protein 18.12% 32.95% Crude fat 5.11% 10.61% Water content 73.45% 41.45% Ash content 3.32% 6.87% Dry weight ratio 26.6% 58.6% * Dry weight = feed -water content 20 (2) Observation of the feed staying in the stomach Seven (7) hours after the feeding, each one of the bluefin tuna was landed from the anchovy-fed group and the core-shell type pellet-fed group, and digestion of the respective feeds in their stomachs was examined. The landed bluefin tunas were larger than 25 the average size, the anchovy-fed tuna weighing 4.7 kg and the core-shell type pellet-fed tuna, 4.5 kg. Photographs showing the digestion condition are appended in place of drawings [(a) showing the feed taken out of the anchovy-fed tuna's stomach, and (b), that taken 19 out of the core-shell type pellet-fed tuna's stomach]. Digestion of anchovies was found considerably progressed, but the core-shell type pellets still retained the pellet shape although with melted surface, and the latter's stay in the stomach for a fixed time was confirmed. 5 Feed Example 2 This Example is a feed intake-determining test in which two kinds of differently shaped core-shell type cylindrical pellets and rectangular parallelepiped pellets (having rectangular cross-section 10 cut along the shorter axis) were fed to 2-year bluefin tunas. (1-1) Preparation of the cylindrical core-shell type pellets used in the test The operations of Production Example 1 were repeated except 15 that the operation mode of the same encrusting machine as used in the Production Example was set at 31.0 and 46.7 (scales on the encrusting machine) for rotation of the motors carrying the shell material and the core material, respectively; the nozzle, at 25 mm; the ring, at 32 mm; and the working interval of the cutter, at once/2 20 seconds; and that a core material in which NEW Weight-Up HCS (tradename, an assorted feed for growing saltwater fish, Mercian Corporation) and chopped frozen fish (selected from anchovies, mackerel and sauries) were mixed at the blend ratio as given in Table 8, to make cylindrical core-shell type pellets of each 32 mm in 25 diameter and 100 mm in length. As to their shape, see (a) and (b) of Photograph 1 as given in place of Fig. 1. (1-2) Preparation of the rectangular parallelepiped core-shell type pellets 30 The operations for preparing the above cylindrical core-shell type pellets were repeated except that the nozzle and ring in the encrusting machine were changed to a 28 mm X 17 mm rectangular nozzle and 36 mm X 22 mm rectangular ring, respectively, to make rectangular parallelepiped pellets of each 36 mm X 22 mm X 100 mm 35 in size (see Photographs a, b and c given as Fig. 3).

20 TABLE 8 Core Blend Ratio Starting material Blend ratio NEW Weight-Up HCS 50.0% Chopped pieces of frozen fish* 50.0% Total 100.0% 5 NEW Weight-Up HCS Feed Additives Used, Blend Ratios and Components Components crude protein at least 23.5% crude fat at least 40.0% 10 crude fiber at least 2.0% crude ash content at least 13.0% calcium at least 1.5% phosphorus at least 1.0% 15 Feed additives contained vitamin A, vitamin D 3 , vitamin E, choline, vitamin C, nicotinic acid, pantothenic acid, inositol, vitamin B 2 , vitamin B 6 , vitamin Bi, folic acid, vitamin B 12 , biotin, vitamin K, iron sulfate, magnesium sulfate, zinc sulfate, manganese sulfate, 20 copper sulfate, aluminum hydroxide, calcium iodide, cobalt sulfate, ethoxyquin 21 Starting materials Blend Ratio Starting Material Animal feed 35.6% fish oil Grain 15.6% wheat flour (off grade) Vegetable oil cakes 5.6% soybean oil cake Chaff and bran 1.1% defatted rice bran Others 42.1% fish oil, vegetable oil and fat, calcium phosphate (2) Test method for feed intake determination 5 To 1,500 2-year bluefin tunas of 14 kg in average body weight as visually estimated, which were cultivated in a net cage [40 m x 25 m x 20 m (depth)] on thawed frozen fishes, 100 each of above-described cylindrical and rectangular parallelepiped core-shell type pellets were fed by throwing with hand, and the state of the 10 tunas' taking the feeds was confirmed. The water temperature was 27.7 0 C, and the weather was fine. (3) Feed-intake test result The test result was as shown in Table 9. In the Table 9, "not 15 taken" means that none of the core-shell type pellets thrown into the net cage was eaten, and "vomited after taking" means the feed once swallowed but vomited. "Taken" means the feed completely swallowed. In this test, about a half of the cylindrical core-shell type pellets were not taken and most of the rest once taken also were 20 vomited, probably because of the temperature change in the seawater immediately before the test. The rectangular parallelepiped core-shell type pellets drifted in the seawater upon landing and swingingly sank in the water. Probably because that manner of sinking stimulated the bluefin tunas' appetite, all of the thrown-in 25 pellets were taken, and while a part of which were once vomited, other bluefin tunas took the vomit and eventually 100% taking was confirmed. This result led to an assumption that rectangular 22 parallelepiped core-shell type pellets rather than cylindrical core-shell type pellets could secure higher feed intake, for bluefin tunas of around 14 kg in body weight. 5 TABLE 9 Shape of tested feed Not taken Vomited after Taken Total __________ taking ____ Cylindrical 52% 45% 3% 100% paraleaepiped 0% 0% 100% 100% Feed Example 3 (1) Preparation of cylindrical core-shell type pellets used in the test 10 The operations of production Example 1 were repeated except that the operation mode of the same encrusting machine as used in Production Example 1 was set at 31.0 and 46.7 (scales on the encrusting machine) for rotation of the motors carrying the shell material and the core material, respectively; the nozzle, at 25 mm; the 15 ring, at 32 mm; and the working interval of the cutter, at once/2 seconds; and that a core material in which NEW Weight-Up HCS (tradename, an assorted feed for growing saltwater fish, Mercian Corporation) and frozen fish (chopped anchovy pieces) were mixed at the blend ratio as given in Table 8, to make cylindrical core-shell type 20 pellets of 32 mm in diameter and 120 mm in length. As to its shape, see (a) and (b) of Photograph 1 as given in place of Fig. 1. (2) Cultivation of tunas In a circular net cage [20 m in diameter X 15 m (depth)], 54 25 bluefin tunas of about 34.5 kg in average body weight were accommodated and cultivated. Because it was difficult to measure the body weight of the living tunas, three of them were landed on the day before starting of the cultivation and their average body weight as measured after their death was posted as the average body weight. 30 23 (3) Result of the cultivation The cultivation achievement in 360 days after starting of the cultivation (water temperature, 15.5 0 C - 27.90C) is shown in the following Table 10. The average body weight of the fish at the end of 5 the cultivation is the average weight of two of them randomly landed on the last day of the cultivation, as measured after death. Feed intake of the core-shell type pellets during the cultivation term was generally good. Twenty-six (26) bluefin tunas so cultivated were sold at markets in Keihan District and Tohoku District, Japan for public 10 evaluation. They were good both in the outlook and quality of the meat. Furthermore, the fish's weight increase rate in this cultivation was equal to that in the case of using frozen fish as the feed. The cause of deaths of the fish during the cultivation is 15 presumed to be their collision with the net cage structure. TABLE 10 Average weight of the fish at the start (kg) 34.5 Average weight of the fish at the end (kg) 71.1 Fish number at the start 54 Fish number at the end 17 Total fish weight in the net cage at the start (kg) 1,863 Total fish weight in the net cage at the end (kg) 1,209 Number of deaths 11 Average weight of dead fish (kg) 51.0 Total weight of dead fish (kg) 561 Number of shipped fish 26 Average weight of shipped fish (kg) 54.67 Given feed (kg) 12,700 Total weight of shipped fish (kg) 1,421 Compensated meat increase coefficient 9.6 Yield 79.6% 24 List of cited references Patent Reference 1: JP 2004-97064A Patent Reference 2: Japanese Patent No. 3243497 Patent Reference 3: JP Hei 8(1996)-280333A 5 Patent Reference 4: JP Sho 62 (1987)-210935A Industrial Applicability According to the invention, feeds in large-sized fish cultivation are provided, which exhibit cultivation effect equaling that of frozen 10 fishes currently used as fish feed such as sardines, mackerel, horse mackerel, sauries and the like. Therefore, the present invention is useful for feed production business and fish cultivation business.

Claims (16)

1. A solid feed for large-sized fishes, which is in core-shell form, the shell being composed of an agglutinant substance containing nutrient for a fish feed, the core being 5 a fish feed itself or containing nutritious component of a fish feed, and the shape of said solid feed corresponds to substantially rectangular parallelepiped or substantially flattened rectangular parallelepiped or substantially flattened cylindrical.

2. The solid feed according to Claim 1, in which, the agglutinant substance is at 10 least one member selected from the group consisting of a-starch, raw starch, wheat gluten, guar gym, carboxymethyl cellulose, gelatin, collagen, carrageenan, sodium alginate, agar and xanthane gum.

3. The solid feed according to Claim 2, in which the agglutinant substance 15 contains at least a-starch.

4. The solid feed according to any one of Clams 1 - 3, in which the nutrient for a fish feed contained in the agglutinant substance is a member or mixture of two or more members selected from the group consisting of fish powder, krill meal, cuttlefish meal, 20 ground fish meat, meat powder, powdered bones, powdered animal matter, grain flour, vegetable oil cake, powdered pulse, chaff and bran, brewage cake, yeast, oil and fat, minced fishes and shellfishes and powdered assorted feed for fisheries use.

5. The solid feed according to any one of Claims 1 - 4, in which the fish feed itself or 25 the composition containing nutritious component of a fish feed is a member or a combination of two or more members selected from the group consisting of fish powder, krill meal, cuttlefish meal, ground fish meat, meat powder, powdered bones, powdered animal matter, grain flour, vegetable oil cake, powdered pulse, chaff and bran, brewage cake, yeast, oil and fat, minced fishes and shellfishes, powdered assorted feed for fisheries 30 use, perishable fishes and shellfishes, frozen fishes and shellfishes; and mash, steam pellet (DP) and extruder pellet (EP) which are produced of at least one of the foregoing. 26

6. The solid feed according to Claim 5, which further contains at least one nutrient selected from the group consisting of vitamin, mineral, amino acid and, optionally growth hormone. 5

7. The solid feed according to Claim 1, in which substantially the whole of the core surface is covered with the shell.

8. The solid feed according to Claim 7, in which the average thickness of the shell portion occupies 5 - 80% of the sectional size of the solid feed (based on the radius when 10 the feed is converted to a spherical matter).

9. The solid feed according to Claim 1, which can be effectively fed by throwing distantly with a pellet feeder, without its shape being broken. 15

10. The solid feed according to Claim 1, which is in frozen state.

11. The solid feed according to Claim 1, which is defrozen after being frozen.

12. The solid feed according to Claim 10 or 11, in which the agglutinant substance is 20 at least one member selected from the group consisting of a-starch, raw starch, wheat gluten, guar gum, carboxymethyl cellulose, gelatin collagen, carrageenan, sodium alginate agar and xanthane gum, and the nutrient for a fish feed contained in said agglutinant substance-is at least one member selected from the group consisting of fish powder, krill meal, cuttlefish meal, ground fish meat, meat powder, powdered hones, 25 powdered animal matter, grain flour, vegetable oil cake, powdered pulse, chaff and bran, brewage cake, yeast, oil and fat, minced fishes and shellfishes and powdered assorted feed for fisheries use.

13. The solid feed according to Claim 12, in which the fish feed itself or the 30 composition containing nutritious component of a fish feed is a member or a combination of two or more members selected from the group consisting of fish powder, krill meal, cuttlefish meal, ground fish meat, meat powder, powdered bones, powdered animal matter, grain flour, vegetable oil cake, powdered pulse, chaff and bran, brewage cake, yeast, oil and fat, minced fishes and shellfishes, powdered assorted feed for fisheries use, 27 perishable fish's and shellfishes, frozen fishes and shellfishes; and mash, steam pellet (DP) and extruder pellet (EP) which are produced of at least one of the foregoing.

14. A method for preparing the solid feed for large-sized fishes according to Claim 5 1, which comprises: (a) a step for formulating a crust material (shell-forming material) by mixing and grinding nutrient for fish feed with an agglutinant substance, adding water to the dough and kneading, (b) a step for preparing a filling, material (core forming material) by using a 10 fish feed itself or a composition containing nutritious component of a fish feed, the composition being added with water and kneaded where necessary, (c) a step for supplying a rod-like feed dough having a double structure of the crust material and filling material as obtained in the steps (a) and (b), to the opening of a crust-cutting apparatus capable of cutting the crust plural times, 15 (d) a step of cutting the crust of the rod-like feed dough at a suitable length, (e) an optional step of further adjusting the crust-cut pieces as obtained in the step (d) into a suitable shape and freezing them, and ) an optional step of defreezing, the frozen solids. 20

15. The solid feed according to any one of Claims 1 - 13, whose cross-section is 2 - 7 cm in diameter and whose longitudinal length is 6 - 30 cm.

16. The solid feed according to any one of Claims 1 - 13 and 15, substantially as 25 hereinbefore described with reference to any of the Examples.