Feed for eel larvae containing a binder

Abstract

The purpose of the present invention was to provide a feed having excellent shape retention and suppressed diffusion in water in order to enhance feeding efficiency of larvae belonging to the order Anguilliformes. Moreover, the present invention has addressed the problem of providing a feed which has favorable shape retention, is favorably fed to larvae belonging to the order Anguilliformes even using various existing feed raw materials or biological feeds having use results in culture, and is finely granulated through washing after being fed so that clogging in a strainer of an exhaust port is also less likely to occur. The present invention includes a feed containing (A) a binder and (B) a nutrient component and having a specific viscosity and a specific viscosity decrease rate when artificial seawater is added and mixed.

Description

Technical Field

[0001] The present invention relates to a feed having viscosity characteristics suitable for feeding larvae of Anguilliformes, and a method for producing larvae of Anguilliformes using the feed.

Background Art

[0002] In general eel farming, glass eels, which are juvenile eels, are caught from the wild and cultured until they become adult eels. However, the catch of glass eels has been decreasing year by year. Therefore, the establishment of a technology for artificially mass-producing glass eels is required.

[0003] For example, eels grow through a preleptocephalus less than 10 mm in total length that grows by nutrition derived from eggs (internal nutrition), and become leptocephalus larvae about 10 mm to 60 mm in body length about 10 days after hatching. Leptocephalus grows and metamorphoses into glass eels, which are juvenile eels.

[0004] At the leptocephalus stage, it is presumed that they feed on marine snow in the wild, but in aquaculture, a feed containing rare shark eggs is exclusively used. However, shark eggs are expensive and may become difficult to procure in the future, which is not desirable for sustainable aquaculture. Furthermore, in aquarium culture, it is required that the water quality and the breeding system be less polluted. On the other hand, shark eggs are suspended in water and tend to pollute the water quality and the breeding system, which has been a problem.

[0005] Against such a background, various feeds have been developed based on commonly used feed ingredients, while suppressing water pollution and improving the palatability for eel leptocephalus. For example, Patent Document 1 discloses an aquaculture feed in which an aqueous phase containing a water-soluble nutrient component is present in an oil phase containing an oil-soluble nutrient component and is microencapsulated as a feed for eel leptocephalus that can be directly fed and does not pollute the breeding water. Also, Patent Document 2 discloses that in order to improve the survival rate of eel larvae, the feed viscosity is 101 ~10 3 is described to be adjusted to mPa·s.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, conventional feed of the diffusing type in breeding water such as capsule type as previously reported has a problem that the feeding efficiency by the larvae of the Anguilliformes is poor. Similarly, the feed as described in Patent Document 2 also has a property of being likely to diffuse in water. When the feed diffuses in water, there is a problem that the strainer installed for the purpose of collecting large floating substances contained in the breeding wastewater is likely to be clogged, and the breeding environment is likely to deteriorate in a short time.

[0008] In view of the above circumstances, an object of the present invention is to provide a feed having excellent shape retention and suppressed diffusion in water in order to improve the feeding efficiency by the larvae of the Anguilliformes. And, together with good shape retention, even when using various existing feed raw materials and live baits with a proven track record in aquaculture, it is also an object of the present invention to provide a feed that is favorably eaten by the larvae of the Anguilliformes and is less likely to cause clogging of the strainer at the drainage outlet by being granulated by washing after feeding.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that a feed containing (A) a binder and (B) a nutritional component and having a viscosity in a specific range has excellent shape retention and is favorably eaten by the larvae of the Anguilliformes. Furthermore, the feed of the present invention is prepared so as to have a viscosity reduction rate of a certain level or less in the breeding water, and thus can be easily granulated by washing after feeding, and it has been found that the feed has excellent washing suitability and does not cause clogging of the strainer at the drain outlet. Based on these findings, the present invention has been completed.

[0010] That is, the present invention provides the following feed for larvae of Anguilliformes. [1] (A) a binder and (B) a nutritional component, The feed for larvae of Anguilliformes has a viscosity at 25°C of 0.12 to 0.37 Pa·s and a viscosity reduction rate of 10% or more and 50% or less when 20 parts by mass of artificial seawater is added to and mixed with 100 parts by mass. [2] The feed according to [1], wherein the (A) binder is at least one selected from the group consisting of xanthan gum, welan gum, deacetyl xanthan gum, fermented cellulose, methyl cellulose, and pectin, and the content of the (A) binder is 0.2 to 1.2%.

[0011] Furthermore, the present invention provides the following method for producing larvae of Anguilliformes. [3] A method for producing larvae of Anguilliformes, comprising feeding the feed according to [1] or [2] to the larvae of Anguilliformes. [4] The production method according to [3], wherein the feed is fed so as to be localized on a part of the bottom surface of the water tank, in the water, or on the water surface. [Advantages of the Invention]

[0012] The feed of the present invention has excellent shape retention even when using various existing feed raw materials with a proven track record in aquaculture, and it enables the larvae of Anguilliformes to efficiently feed in a short time. Furthermore, since it can be easily granulated by washing after feeding, it is less likely to cause clogging of the strainer at the drain outlet, has excellent washing suitability, and can reduce the labor of breeding management. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0014] [Definition] In this specification, "feed" and "bait" have the same meaning, and both refer to substances that are orally ingested and contain one or more nutrients that enable the growth, reproduction, spawning, etc. of aquatic animals, etc., and contain almost no harmful substances.

[0015] In this specification, "larval fish" refers to fish from after hatching until all fins are fully developed. The larval fish of the eel order are called leptocephali.

[0016] In this specification, "leptocephalus" refers to "leaf-shaped larval fish", which is a characteristic juvenile form of fish belonging to the cohort Elopomorpha including the eel order (Anguilliformes). Leptocephali generally have the characteristics of being willow-leaf-shaped and transparent.

[0017] In this specification, "shape retention" refers to the property that the shape of the feed is maintained for a certain period of time even after feeding the target organism (for example, eel larvae). A feed with high "shape retention" can efficiently allow eel larvae to ingest nutrients because the nutrient components contained therein are difficult to diffuse into the breeding water. In this specification, "washability" refers to the property that the feed collapses and is refined by washing using an artificial water flow (not particularly limited, for example, a water flow created by a pump) that is significantly stronger than the water flow caused by the movement of the larvae. Therefore, for example, "good in terms of shape retention and washability" means that even when the eel larvae feed, the feed is prevented from diffusing and decreasing in the water, while it easily disintegrates and becomes finer by washing after feeding.

[0018] [Feed for Larval Eels] The feed of the present invention is for larval eels and contains (A) a binder and (B) nutritional components, has a viscosity within a specific range, and is characterized in that the viscosity reduction rate when artificial seawater is added and mixed is a certain value or less.

[0019] (Target) The target of the feed of the present invention is larval eels.

[0020] Examples of the order Anguilliformes include, for example, the families Anguillidae, Muraenesocidae, Congridae, Muraenidae, and Ophichthidae. Among them, as the target of the present invention, one or more fish species selected from the group consisting of the families Anguillidae, Muraenesocidae, and Congridae are preferred, and fish of the family Anguillidae are more preferred.

[0021] The fish of the family Anguillidae that are the target of the present invention are preferably fish of the genus Anguilla. Specific examples of fish of the genus Anguilla are not particularly limited, but include Anguilla japonica, Anguilla anguilla, Anguilla rostrata, Anguilla marmorata, and Anguilla bicolor pacifica. Among them, Anguilla japonica is preferred.

[0022] The fish of the family Muraenesocidae that are the target of the present invention are preferably Muraenesox cinereus.

[0023] The fish of the family Congridae that are the target of the present invention are preferably Conger myriaster.

[0024] The body length of the eel fry is not particularly limited, but from the viewpoint of significantly exhibiting the effects of the present invention, it is preferably 8 mm or more, more preferably 9 mm or more, and still more preferably 10 mm or more.

[0025] The body length of the eel fry is not particularly limited, but it can be, for example, 60 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, or 20 mm or less.

[0026] The number of days (age) after hatching of the eel fry is not particularly limited, but from the viewpoint of significantly exhibiting the effects of the present invention, it is preferably 8 to 300 days, more preferably 15 to 250 days, and still more preferably 20 to 200 days.

[0027] (Physical properties) The viscosity of the feed of the present invention at 25°C is, from the viewpoint of significantly exhibiting the effects of the present invention, for example, 0.37 Pa·s or less, 0.36 Pa·s or less, or 0.35 Pa·s or less, and 0.12 Pa·s or more, 0.13 Pa·s or more, or 0.14 Pa·s or more. The higher the viscosity, the better the "shape retention" of the feed. However, if the viscosity is too high, the eel fry may not be able to ingest the feed, and the "ingestion amount" may decrease. However, even if the viscosity is high, for example, when a binder with a high viscosity reduction rate such as sodium carboxymethylcellulose (CMC-Na) is used, the feed may be ingested during the process of viscosity reduction after being placed in water. On the other hand, the lower the viscosity of the feed, the better the "washing suitability" of the feed. However, if the viscosity is too low, the feed may easily diffuse in water and may not be ingested by the eel fry, and the "ingestion amount" may decrease. Since the "viscosity" of the feed is related to all of "shape retention", "washing suitability" and "ingestion amount" in this way, it is necessary to adjust it to the above viscosity range. In this specification, the viscosity is measured by the method and conditions described in the examples.

[0028] When 20 parts by mass of artificial seawater is added to 100 parts by mass of the feed of the present invention and mixed at 25°C, the viscosity reduction rate is, from the viewpoint of significantly exhibiting the effects of the present invention, for example, 50% or less, 49% or less, 48% or less, 47% or less, 46% or less, 45% or less, 40% or less, 35% or less, or 32% or less, and 10% or more, 12% or more, 15% or more, 16% or more, 17% or more, or 18% or more. The higher the viscosity reduction rate, the faster the viscosity decreases after the feed is placed in water. Therefore, while a feed with too high a viscosity reduction rate has the advantage of high "washing suitability", it is difficult to maintain the "shape retention" of the feed even when the viscosity of the feed is set high. On the other hand, a feed with too low a viscosity reduction rate has a small degree of viscosity reduction after the feed is placed in water, so while it has good "shape retention", its "washing suitability" is poor. Since the viscosity reduction rate of the feed is thus related to all of "shape retention", "washing suitability", and "feeding amount", it is necessary to adjust it within the above range of the viscosity reduction rate. Here, in this specification, the above viscosity reduction rate is measured by the methods and conditions described in the examples.

[0029] ((A) Binder) The binder, which is the component (A) of the present invention, is not particularly limited as long as it can impart the above physical properties. Examples include polysaccharides that easily dissolve when mixed with distilled water at room temperature (15 to 40°C). Specifically, xanthan gum, deacetylated xanthan gum, fermented cellulose, alginates (sodium salt, potassium salt, or ammonium salt), carrageenan, pectin, soy polysaccharides, welan gum, galactomannans (e.g., guar gum, etc.), tamarind seed gum, cellulose derivatives (e.g., hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl ethylcellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, ethyl cellulose, methyl cellulose, water-soluble hemicellulose, etc.), starches (e.g., starch, carboxymethyl starch, hydroxypropyl starch, octenyl succinic anhydride starch, acetic acid starch, etc.) and dextrins (e.g., polydextrose, resistant dextrin, etc.) can preferably be used alone or in combination of two or more selected from the group consisting of. However, since the physical properties of polysaccharides may change depending on the environment in which they are used, the use of polysaccharides other than those described above is not excluded.

[0030] Furthermore, since the viscosity of the feed may be affected by the viscosity of feed components other than the above binders (e.g., sodium caseinate, etc.), when designing the feed, the type and addition amount of the binder may be appropriately adjusted according to the composition of the feed components. Therefore, as a preferred embodiment of the present invention, there is provided a feed for juvenile eels containing (A) a binder and (B) a nutritional component (including at least sodium caseinate), having a viscosity at 25°C of 0.12 to 0.37 Pa·s, and a viscosity reduction rate of 50% or less when 20 parts by mass of artificial seawater is added to and mixed with 100 parts by mass.

[0031] On the one hand, when using a polysaccharide with a large viscosity reduction rate in water, even if the feed formulation is set to increase the viscosity, it has the property of being easily diffusible in water. When preparing the feed of the present invention using such a polysaccharide with a large viscosity reduction rate in water, detailed consideration may be required to adjust it to the desired properties. Therefore, the polysaccharide that can preferably be used when preparing the feed of the present invention is a polysaccharide with a viscosity reduction rate in water smaller than a certain level. For example, xanthan gum (Sun Ace (registered trademark), manufactured by San-Ei Gen F.F.I., Inc.), welan gum (Vistop (registered trademark) D-2419, manufactured by San-Ei Gen F.F.I., Inc.), deacetyl xanthan gum (Sun Ace (registered trademark) NXG-S, manufactured by San-Ei Gen F.F.I., Inc.), fermented cellulose (Sun Artist (registered trademark) H-PG, manufactured by San-Ei Gen F.F.I., Inc.), methylcellulose (Vistop (registered trademark) D-4187, manufactured by San-Ei Gen F.F.I., Inc.), pectin (Vistop (registered trademark) D-2264, manufactured by San-Ei Gen F.F.I., Inc.), etc. can be mentioned.

[0032] The content of the binder in the feed of the present invention is not particularly limited and can be appropriately adjusted according to the types of nutritional components and binders. For example, it may be 0.1% by mass or more, 0.12% by mass or more, 0.2% by mass or more, or 0.3% by mass or more based on the total amount of the feed. From the viewpoint of significantly exhibiting the effects of the present invention, it is preferably 0.31% by mass or more, more preferably 0.35% by mass or more. The content of the binder in the feed of the present invention is not particularly limited and may be, for example, 2% by mass or less, 1% by mass or less based on the total amount of the feed. From the viewpoint of significantly exhibiting the effects of the present invention, it is preferably 0.74% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.65% by mass or less. More specifically, the content of the binder in the feed of the present invention is a combination of the above lower limit value and upper limit value based on the total amount of the feed. For example, it is 0.12 to 1.2% by mass.

[0033] ((B) Nutritional components) As the nutritional components used in the component (B) of the feed of the present invention, there is no particular limitation as long as the effects of the present invention are not impaired. For example, protein raw materials such as proteins derived from aquatic organisms, proteins derived from eggs, proteins derived from milk, proteins derived from grains, etc.; oils and fats such as fish oil and cod liver oil; amino acids such as taurine, etc.; vitamins, etc. may be mentioned. These nutritional components may be used alone, or two or more of them may be used in combination.

[0034] Examples of proteins derived from aquatic organisms include fish meal, eggs of fish (eggs of sharks, sea breams, eels, etc.), fish meat protein hydrolysates, krill hydrolysates or raw shirasu, in the form of powder or paste, etc.

[0035] Examples of proteins derived from eggs include whole eggs (such as chicken eggs), egg yolks, egg whites, albumin, etc.

[0036] Examples of proteins derived from milk include casein (including salts), skim milk powder, whole milk powder, milk, milk protein concentrate (MPC), whey protein (whey), etc.

[0037] Examples of proteins derived from grains include soy peptides, soy proteins, etc.

[0038] The feed of the present invention preferably contains at least a protein raw material as a nutritional component. Among them, it is preferable to contain at least one or two or more raw materials selected from the group consisting of proteins derived from aquatic organisms, proteins derived from eggs, proteins derived from milk, and proteins derived from grains, and more preferably to contain at least one or two or more selected from the group consisting of eggs of Squalus suckleyi, chicken eggs, sodium caseinate, and soy peptides.

[0039] The content of the nutritional component is not particularly limited and can be appropriately adjusted according to the types of the nutritional component and the binder. However, it is preferably 2 to 99.99% by mass, more preferably 5 to 90% by mass, still more preferably 8 to 85% by mass, and particularly preferably 10 to 80% by mass based on the total amount of the feed.

[0040] (Water content) The water content of the feed of the present invention is not particularly limited, but is preferably 20 to 95% by mass.

[0041] (Form) The feed of the present invention is preferably in the form of a paste. In addition, the paste form may generally be expressed as a slurry form or a suspension state.

[0042] The feed of the present invention may be frozen. In such a case, the physical properties defined in the present invention are designed to be exhibited when thawed.

[0043] (Suspensibility in a dissolution tester) From the viewpoint of good shape retention and washing suitability, when the feed of the present invention is tested under the following conditions using a dissolution tester used in pharmaceutical tests, it is preferable that the feed mass is maintained at the bottom after 15 minutes and the mass is not visible at the bottom after 30 minutes. <Conditions> Using a dissolution tester PJ-32S (manufactured by Miyamoto Riken Kogyo Co., Ltd.), put 3 mL of the feed at the bottom of a dedicated vessel containing 900 mL of artificial seawater (Marine Art SF-1; diluted with ion-exchanged water manufactured by Tomita Pharmaceutical Co., Ltd. to a concentration of 37 g / L), and stir with a dedicated paddle shaft at 40 rpm for 30 minutes. Visually observe the turbidity of the feed and artificial seawater over time. At the same time, sample 3.5 cm from the water surface of the artificial seawater at an arbitrary stirring time with a dropper and put it into a cuvette, and also measure the transmittance at 720 nm using a spectrophotometer (V-560, manufactured by JASCO Corporation).

[0044] (Feeding and recovery method) The feed of the present invention can be recovered after the feeding is completed. And since there is little diffusion into the water when the feed is ingested, water quality maintenance management is simple and low-cost. When using the feed of the present invention in an aquarium with water supply and drainage, a part of the feed dispersed in the water is less likely to clog the strainer (net) at the drain outlet, etc., and can be removed from the aquarium together with the drainage.

[0045] In addition, since the feed of the present invention has high palatability, it is applicable to various feeding methods. The feed of the present invention is not particularly limited. For example, it is also possible to feed in a lump at one place on the bottom surface or in the water. According to such a feeding method, even in a large-scale aquarium, a small amount of feed is sufficient, and complicated equipment is not required.

[0046] (Manufacturing method) The feed of the present invention is obtained by adding and mixing water and other components to components (A) and (B) as appropriate.

[0047] In addition, the manufacturing method of the present invention may include a sterilization step, a packaging step, a freezing step, and the like.

[0048] As a specific embodiment of the present invention, examples of the feed include those containing xanthan gum, welan gum, deacetyl xanthan gum, fermented cellulose, methyl cellulose, or pectin as component (A) and a protein raw material as component (B). As a more preferable embodiment, examples of the feed include those containing at least sodium caseinate as component (B).

[0049] In one aspect, the protein content is preferably 30 to 90% by mass, more preferably 40 to 80% by mass, and still more preferably 50 to 70% by mass based on the total dry weight of the feed. The type of protein is not particularly limited. Examples of the material containing the protein component include fish meal or shark eggs. Since the materials containing the protein component have different viscosities, the type and concentration of the thickener used can be appropriately changed according to the type of the material used. In one aspect, from the viewpoint of significantly demonstrating the effects of the present invention, the xanthan gum content is 0.35 to 0.8% by mass, 0.35 to 0.9% by mass, or 0.40 to 0.9% by mass based on the total amount of the feed. In one aspect, from the viewpoint of significantly demonstrating the effects of the present invention, the welan gum content is 0.3 to 0.7% by mass, 0.4 to 0.7% by mass, or 0.44 to 0.64% by mass based on the total amount of the feed. In one aspect, from the viewpoint of significantly achieving the effects of the present invention, the content of deacetylated xanthan gum is 0.2 to 0.6% by mass, 0.2 to 0.7% by mass, 0.3 to 0.7% by mass, or 0.35 to 0.7% by mass based on the total amount of the feed. In one aspect, from the viewpoint of significantly achieving the effects of the present invention, the content of fermented cellulose is 0.3 to 0.7% by mass based on the total amount of the feed. In one aspect, from the viewpoint of significantly achieving the effects of the present invention, the content of methylcellulose is 0.7 to 1.0% by mass, 0.7 to 1.1% by mass, or 0.74 to 1.2% by mass based on the total amount of the feed. In one aspect, from the viewpoint of significantly achieving the effects of the present invention, the content of pectin is 0.7 to 1.1% by mass, 0.8 to 1.1% by mass, or 0.8 to 1.2% by mass based on the total amount of the feed.

[0050] [Method for producing larvae of Anguilliformes] The method for producing larvae of Anguilliformes of the present invention includes feeding the feed described in the above section of [Feed for larvae of Anguilliformes] to the larvae of Anguilliformes. According to the production method of the present invention, the labor for rearing management of the larvae of Anguilliformes can be reduced. More specifically, since the diffusion of the feed in water is suppressed, the larvae of Anguilliformes can be efficiently fed. Furthermore, the contamination of water and the rearing system can be suppressed, and the deterioration of the rearing environment can be prevented, thereby reducing the frequency of cleaning the rearing tank.

[0051] Examples of the water supply and drainage method of the water tank include a flowing-through type and a circulating type, but the flowing-through type is preferred. In a flowing-through type water tank, when using a diffused (floating) feed, the strainer (net) usually provided at the drain outlet may become clogged, but in the production method of the present invention, the clogging of the strainer is suppressed by the effect of the feed of the present invention.

[0052] The number of feedings per day is not particularly limited and can be appropriately changed according to the age of the rearing target. In the case of eel larvae, it is preferably 1 to 10 times a day, more preferably 5 times a day.

[0053] The production method of the present invention preferably includes feeding in a state where feed is localized in an aquaculture tank such as an aquarium. The feeding mode is not particularly limited. For example, the feed can be localized on the water surface, in the water, or on a part of the bottom surface of the aquarium. When localizing, it can be in a mode such as leaving the feed stationary uncovered, putting it in a feed container, a net, etc. and installing it on the water surface, in the water, or on the bottom surface of the aquarium, etc.

[0054] Furthermore, the production method of the present invention preferably includes a step of pulverizing the feed by the water flow after the eel fry have fed, with the above aquarium being equipped with a mechanism for forming a water flow. By including this step, the feed can be easily removed from the aquarium water by the water flow. As such a water flow, for example, the water flow associated with the above water supply and drainage is used.

[0055] Regarding the eel - order fish targeted by the production method of the present invention, as well as the details and preferred embodiments of the feed, they are as described in the above section of [Feed for Eel - order Fry].

Examples

[0056] Hereinafter, the present invention will be described in more detail using examples. However, these examples do not limit the present invention. In the examples, "parts" and "%" respectively mean "parts by mass" and "mass %". Also, the "*" mark in the text indicates that it is manufactured by Samwon FF - I Co., Ltd., and the "※" mark in the text indicates that it is a registered trademark of Samwon FF - I Co., Ltd.

[0057] [Materials and Methods] (Preparation of Samples) For the feed, feed samples with various viscosities and viscosity reduction rates were prepared using the binders in Tables 1 and 2 of the test examples. The composition and content of the nutritional components of the prepared feed samples (solid content 14.5 mass %, protein 8.8 mass %) are the same for all except Comparative Example 1. The procedure for preparing the samples is as follows. <Preparation Procedure> (1) To the powder mixture obtained by premixing all raw materials except the ion-exchanged water in Table 3, ion-exchanged water was added and stirred at room temperature to prepare a solution containing nutrients at a final concentration twice as high. For Comparative Example 1 without adding a binder, the nutrient solution was used without dilution. (2) A binder was added to ion-exchanged water and stirred at room temperature for 10 minutes to dissolve it. For feeds other than Comparative Example 1, they were stirred and mixed with the solution in (1) at a ratio of 1:1.

[0058] (Viscosity measurement method) Viscosity was measured using a rotational rheometer MCR302 (manufactured by Anton Paar). As the plate, a 50 mm cone plate (cone angle 1°, manufactured by Anton Paar, CP50-1) was used. The measurement was carried out under the conditions of a gap (sample thickness) of 0.1 mm, both the air temperature and the sample temperature of 25 °C, and a shear rate of 50 s -1 and.

[0059] (Measurement method of viscosity reduction rate) When 20 parts by mass of artificial seawater was added to 100 parts by mass of the feed and mixed at 25 °C, the viscosity reduction rate of the feed was measured according to the following procedure. (1) According to the above viscosity measurement method, the viscosity η1 (Pa·s) of the feed before adding water was measured. (2) To 100 parts by mass of the feed, 20 parts by mass of artificial seawater (Marine Art SF-1; diluted with ion-exchanged water and adjusted to a concentration of 37 g / L by Toyoda Pharmaceutical Co., Ltd.) was added and mixed well to prepare a water-added mixture. (3) According to the above viscosity measurement method, the viscosity η2 (Pa·s) of the obtained water-added mixture was measured. (4) From η1 and η2, the viscosity reduction rate (%) was calculated according to the following calculation formula. <Viscosity reduction rate> Viscosity reduction rate (%) = (η1 - η2) / η1 × 100

[0060] (Evaluation of palatability) The feed was fed to the fry of Japanese eels according to the following procedure to evaluate the palatability. The feeding was carried out at 25 °C. (1) Ten 100-day-old fry were placed in a 10 L water tank, and the sample was left standing at the bottom of the water tank. (2) Seven minutes after feeding, the fry were collected and anesthetized with 2-phenoxyethanol. (3) The amount of residue in the digestive tract of the fry was quantified using transmitted light. When observing the fry with transmitted light, since the whole body including the digestive tract transmits light, the ingested feed is observed as a dark tubular image. The more feed present in the esophagus, the more it indicates a large feeding amount. Therefore, the feeding performance was evaluated according to the following criteria. Note that the feed with an evaluation of 0 points was evaluated as unsuitable. <Evaluation of feeding performance> 2: The digestive tract is mostly filled with feed. 1: Feed can be confirmed in part of the digestive tract. 0: No feed can be confirmed in the digestive tract.

[0061] (Evaluation of feed form retention) 10 ml of paste-like feed was gently extruded onto the bottom of a 10 L water tank with a pipette and left standing for 10 minutes. Then, the form of the feed was checked, and the feed form retention was evaluated according to the following criteria. Note that the feed with an evaluation of 0 points was evaluated as unsuitable. <Evaluation criteria for form retention> 2: The water maintains transparency and the outline of the remaining feed is clear. 1: Some suspension has progressed, but the remaining feed can be seen at the bottom. 0: Completely suspended and no remaining feed exists in a clumped state.

[0062] (Evaluation of feed washability) 10 ml of paste-like feed was gently extruded onto the bottom of a 10 L water tank with a pipette and left standing for 10 minutes. Then, the feed residue was crushed and suspended with running water (0.6 L / min), and the water was replaced over 1 hour (the water flow rate and drainage volume were 0.6 L / min). From the amount and state of the remaining feed after replacing the water, the washability was evaluated according to the following criteria. Note that the feed with an evaluation of 0 points was evaluated as unsuitable. <Evaluation criteria for washability> 2: No remaining feed can be seen. 1: Some remaining feed can be seen, but it can be washed away by continuing the water flow. 0: Leftover feed remains in large chunks, making it difficult to clean even with continuous water flow.

[0063] [Test Example 1-1. Comparison of Feed Intake, Shape Retention, and Washability of Each Feed] For the feeds prepared according to the formulations shown in Tables 1 and 2, the feed intake, shape retention, and washability were evaluated according to the above method. The feeds (Examples 1 to 5) that were excellent in all items of feed intake, shape retention, and washability had a relatively low viscosity (0.14 to 0.35 Pa·s) before feeding (i.e., unhydrated, 25°C), but it was also revealed that the viscosity did not decrease rapidly after being added to the breeding water (i.e., when hydrated by 20%) (18.8% to 31.3%). Examples 6 to 9 were also excellent in feed intake and shape retention. And according to the results of the permeation rate after 5 minutes and 30 minutes of stirring in the following elution test, the washability of these examples was also good. Feeds having the same viscosity as the examples and the viscosity reduction rate (%) when hydrated by 20% can be prepared by adjusting the addition amount using a desired binder (for example, Examples 1, Comparative Examples 7 and 8). On the other hand, with some binders (for example, CMC-Na; Comparative Examples 2 to 6), feeds having the same physical properties as the feeds of the present invention could not be prepared. When using such binders, it seems that extremely strict condition studies are necessary.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] [Test Example 1-2. Examination of the Estimation Method for Shape Retention and Washability Using Equipment] Regarding some of the feeds in Table 1 and Table 2, it was examined whether the shape retention and washability could be estimated using an elution tester separately used in pharmaceutical tests. The elution tester used was PJ-32S (manufactured by Miyamoto Riken Kogyo Co., Ltd.).

[0068] 3 mL of feed was placed at the bottom of a dedicated vessel containing 900 mL of artificial seawater (Marine Art SF-1; diluted with ion-exchanged water and adjusted to a concentration of 37 g / L by Tomita Pharmaceutical Co., Ltd.), and stirred at 40 rpm for 30 minutes with a dedicated paddle shaft. The turbidity of the feed and artificial seawater was visually observed over time. As shown in Figure 2, it became clear that the shape retention and washability of the feed could be estimated. For example, a feed that maintains a lump at the bottom until 15 minutes later and the lump cannot be seen at the bottom after 30 minutes has good shape retention and washability. In addition, the measurement of transmittance was also carried out as an objective evaluation method. Under the conditions of the above elution tester, the artificial seawater at a position 3.5 cm from the water surface was sampled with a pipette and put into a cuvette 5 minutes and 30 minutes after stirring, and the transmittance at 720 nm was measured using a spectrophotometer (V-560, manufactured by JASCO Corporation). The results are shown in Table 1 and Table 2. A feed with a high transmittance without diffusion 5 minutes later and a low transmittance 30 minutes later has good shape retention and washability.

Claims

1. containing (A) a binder and (B) a nutrient component, a feed for larvae of Anguilliformes having a viscosity at 25°C of 0.12 to 0.37 Pa·s and a viscosity reduction rate of 50% or less when 20 parts by mass of artificial seawater is added to and mixed with 100 parts by mass.

2. The feed according to claim 1, which is in paste form.

3. A method for producing larvae of Anguilliformes, comprising feeding the feed according to claim 1 or 2 to larvae of Anguilliformes.

4. The production method according to claim 3, wherein the feed is fed so as to be localized on a part of the bottom surface of the water tank, in the water or on the water surface.

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