Feed for eel larvae containing gelling agent

Abstract

To provide a method for breeding larvae of Anguilliformes at low cost, and provide inexpensive feed that is less likely to diffuse in breeding water, and attracts and is eaten by the larvae of Anguilliformes.SOLUTION: Jelly feed for larvae of Anguilliformes contains (A) a gelator and (B) a nutritional composition. In an indentation test, when the feed is pressed at 20°C at 1% strain, the load is 0.05-0.68 N. In a dynamic viscoelasticity test, the feed has a loss tangent (tanδ) of 0.14-0.67 at 20°C and at 1 Hz frequency.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a jelly-like feed suitable for feeding eel larvae, and a method for raising eel larvae by feeding the feed to the eel larvae. [Background technology]

[0002] In typical eel farming, glass eels (young eels) are caught in the wild and then cultivated until they reach adulthood, but the catch of glass eels is declining year by year, which has led to a demand for the establishment of technology to artificially produce glass eels.

[0003] For example, eels grow as preleptocephali, less than 10 mm in length, using nutrients derived from eggs (internal nutrients), and then about 10 days after hatching, they become leptocephali (larval eels), which are about 10-60 mm in length. The leptocephali grow and metamorphose into glass eels (juvenile eels), which then grow further into adult eels.

[0004] Leptocephalus (larval eels) are thought to feed on marine snow in the wild, but in aquaculture they are fed exclusively with a diet containing the rare spiny dogfish. However, shark eggs are expensive and may become difficult to procure in the future, making them undesirable for sustainable aquaculture. Furthermore, shark eggs tend to become suspended in the breeding water, deteriorating water quality and contaminating the breeding system.

[0005] Against this background, various feeds have been developed that are based on widely used, inexpensive feed ingredients and have improved palatability for leptocephali. For example, Patent Document 1 describes a method for producing a viscous liquid having a viscosity of 10 1 ~10 3Patent Document 2 discloses a microencapsulated aquaculture feed in which an aqueous phase containing water-soluble nutrients is contained in an oil phase containing oil-soluble nutrients, as feed for leptocephalus that can be directly administered and does not contaminate the rearing water. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2019-154319 [Patent Document 2] International Publication No. 2016 / 117690 Summary of the Invention [Problem to be solved by the invention]

[0007] The diffusion-type feed described in Patent Documents 1 and 2 disperses in the rearing water in aquarium culture, so much of the feed is not ingested by the larvae, and in a recirculating aquarium, it is captured by the filtration filter, resulting in low ingestion efficiency. Because diffusion-type feed disperses in the rearing water, it deteriorates the water quality of the rearing water and is prone to contaminating the rearing system. This causes problems, such as the death of larvae due to the deterioration of the water quality, and the excessive costs of replacing the deteriorated rearing water and purifying the rearing system. On the other hand, there is a problem in that existing non-diffusible feed is not preferred by larval eels due to their unique morphology and ecology.

[0008] Therefore, the present invention relates to providing a feed that is favorably ingested by larval eels of the order Anguilliformes and that is inhibited from dispersing in water, even when using various existing feed ingredients that have a proven track record of use in aquaculture. [Means for solving the problem]

[0009] The present inventors conducted extensive research to solve the above-mentioned problems and found that a jelly-like feed containing a gelling agent and a variety of inexpensive feed ingredients with a proven track record of use in aquaculture as nutritional ingredients, the jelly-like feed having a specific indentation hardness (assessed by an indentation test) and a specific dynamic viscoelasticity (assessed by a dynamic viscoelasticity test), is preferred by larval fish of the order Anguilliformes, and that the diffusion of the feed in water is suppressed. Based on these findings, the present invention was completed. Specifically, the present invention is as follows:

[0010] [1] A jelly-like feed for larval eels of the order Anguilliformes, comprising (A) a gelling agent and (B) a nutritional component, In a compression test, the load when the feed was compressed by 1% strain at 20°C was 0.05 to 0.68 N, A jelly-like feed, wherein the loss tangent (tanδ) of the feed at 20°C and a frequency of 1 Hz is 0.14 to 0.67 in a dynamic viscoelasticity test. [2] The feed according to [1], wherein the gelling agent (A) contains a water-soluble polysaccharide containing, as a constituent sugar, one or more acidic sugars selected from the group consisting of psyllium seed gum, xanthan gum, gellan gum, carrageenan, alginic acid, hyaluronic acid, chondroitin sulfate, fucoidan, pectin, soybean polysaccharides, welan gum, carboxymethyl starch, phosphorylated starch, phosphate cross-linked starch, starch octenyl succinate, and starch acetate, and salts thereof. [3] The jelly feed according to [1] or [2], wherein the nutritional component (B) contains sodium caseinate. [4] A method for raising eel larvae, comprising the step of feeding the jelly feed according to any one of [1] to [3] to the eel larvae. [5] The method according to [4], wherein the larvae of the Anguilliformes are reared in a closed circulation tank. [Effects of the Invention]

[0011] The feed of the present invention is made from inexpensive feed that is inhibited from diffusing in the rearing water and is preferred by larval fish of the order Anguilliformes. Because diffusion in the rearing water is inhibited, feeding efficiency is high and deterioration of the rearing water quality and contamination of the rearing system are suppressed. Therefore, excessive costs incurred for replacing deteriorated rearing water and purifying the rearing system are suppressed. In addition, since inexpensive feed is used as a raw material, larval fish of the order Anguilliformes can be reared inexpensively using the feed of the present invention or by the rearing method of the present invention. [Brief explanation of the drawings]

[0012] [Figure 1] These are photographs of the reference diet to demonstrate the standard of diet diffusibility. Each photograph was taken 15 minutes after the reference diet was placed in water. [Figure 2] In Test Example 2, the appearance of the feed was photographed after it was prepared by mixing the gelling agent and nutritional ingredients and then refrigerated for one day. [Figure 3] 10 is a photograph showing the relationship between the physical properties of the feed and its diffusibility in rearing water in Test Example 3. The photograph was taken after stirring in artificial seawater for 15 minutes using a dissolution tester. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Jelly feed for eel larvae [Larvae of the Anguilliformes] "Larva" refers to the stage of a fish after hatching until all fins are fully developed. Larvae of eels are called leptocephali. "Leptocephali" refers to the "leaf-shaped larvae" that are characteristic of the juvenile form of fishes belonging to the Cohort Elopomorpha, which includes the order Anguilliformes. Leptocephali are generally characterized by their willow-leaf shape and transparency.

[0014] Examples of the Anguilliformes include the families Anguillidae, Muraenesocidae, Congridae, Muraenidae, and Ophichthidae. Of these, the subject of the present invention is preferably one or more fish species selected from the group consisting of Anguillidae, Congridae, and Conger Eels, and more preferably fish species of the Anguillidae family.

[0015] The fish of the Anguillidae family are preferably fish of the genus Anguilla. Specific examples of fish of the genus Anguilla include, but are not limited to, the Japanese eel (Anguilla japonica), the European eel (Anguilla anguilla), the American eel (Anguilla rostrata), the giant mottled ... The fish of the family Porgonidae is preferably the conger eel (Muraenesox cinereus). The fish of the Conger family is preferably the Japanese conger eel (Conger myriaster).

[0016] The body length of the eel larvae is not particularly limited, but from the viewpoint of significantly achieving the effects of the present invention, it is preferably 8 mm or more, more preferably 9 mm or more, and even more preferably 10 mm or more. The body length of the eel larvae is not particularly limited, but may be, for example, 60 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, or 20 mm or less.

[0017] The number of days (age) after hatching of the Anguilliformes larvae is not particularly limited, but from the viewpoint of significantly achieving the effects of the present invention, it is preferably 8 to 300 days, more preferably 15 to 200 days, and even more preferably 20 to 120 days.

[0018] [Jelly feed] The jelly-like feed for eel larvae of the present invention contains (A) a gelling agent and (B) a nutritional component, and is characterized by exhibiting a specific load value in an indentation test and a specific loss tangent in a dynamic viscoelasticity test. In this specification, "feed" and "feeding agent" have the same meaning, and both refer to a substance that is orally ingested by animals, contains one or more nutrients that enable the growth, reproduction, spawning, etc. of aquatic animals, etc., and contains almost no harmful substances.

[0019] The jelly-like feed for eel larvae of the present invention is solid and jelly-like (gel-like). Because diffusion in the rearing water is suppressed, feeding efficiency is high, deterioration of the rearing water quality and contamination of the rearing system are suppressed, and excessive costs incurred for replacing deteriorated rearing water and purifying the rearing system are reduced.

[0020] ((A) Gelling agent) The gelling agent (A) is not particularly limited as long as it can form a jelly state, with a load of 0.05 to 0.68 N in an indentation test, and a loss tangent (tanδ) of 0.14 to 0.67 in a dynamic viscoelasticity test. Examples of such gelling agents include polysaccharides that are easily dissolved when mixed with hot distilled water (60°C or higher).

[0021] Specific examples include psyllium seed gum, xanthan gum, gellan gum, carrageenan, alginic acid, hyaluronic acid, chondroitin sulfate, fucoidan, pectin, soybean polysaccharides, welan gum, agaropectin, karaya gum, porphyran, galactomannans (e.g., locust bean gum, guar gum, tara gum, etc.), tamarind seed gum, glucomannan, macrophomopsis gum, pullulan, curdlan, tragacanth gum, ghatti gum, gum arabic, arabinogalactan, furcellaran, cellulose derivatives (e.g., hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxypropyl ethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, ethyl cellulose, methyl cellulose, water-soluble hemicellulose, etc.), starches (e.g., starch, carboxymethyl starch, hydroxypropyl starch, pregelatinized starch, phosphorylated starch, phosphate cross-linked starch, octenyl succinate starch, acetate starch, etc.), dextrins (e.g., polydextrose, resistant dextrin, etc.), fermented cellulose, microcrystalline cellulose (microfibrous cellulose), hemicellulose, plant-derived dietary fiber (fruit-derived dietary fiber (citrus fiber, apple fiber, grape seed fiber, etc.), grain-derived dietary fiber (wheat fiber, sugarcane fiber, oat fiber, etc.), vegetable-derived dietary fiber (beet fiber, pea fiber, etc.)), chitin, and water-insoluble glucans, and salts thereof, can be selected alone or in combination of two or more.

[0022] Since the physical properties of some polysaccharides change depending on the environment in which they are used, the use of polysaccharides other than those mentioned above is not excluded. Furthermore, the physical properties of the jelly feed may be affected by the physical properties (e.g., viscosity) of (B) nutritional components (e.g., sodium caseinate) other than the (A) gelling agent. Therefore, when preparing the feed, it is preferable to adjust the type and amount of gelling agent added appropriately depending on the feed composition.

[0023] One preferred embodiment of the present invention is a jelly feed for larval fish of the order Anguilliformes, which contains (A) a gelling agent and (B) a nutritional component (including at least sodium caseinate), and in an indentation test, exhibits a load of 0.05 to 0.68 N when indented at 20°C to a strain of 1%, and a loss tangent (tanδ) of 0.14 to 0.67 at 20°C and a frequency of 1 Hz.

[0024] From the viewpoint of imparting the above-mentioned physical properties, the gelling agent (A) of the present invention is preferably one or more selected from the group consisting of psyllium seed gum, xanthan gum, gellan gum, carrageenan, alginic acid, hyaluronic acid, chondroitin sulfate, fucoidan, pectin, soybean polysaccharides, welan gum, carboxymethyl starch, phosphorylated starch, phosphate cross-linked starch, starch octenyl succinate, starch acetate, and salts thereof.

[0025] Psyllium seed gum is a water-soluble polysaccharide extracted from the seeds of plants in the Plantago genus, primarily blond psyllium (Plantago ovata Forskal). Psyllium seed gum is extracted from the husk that surrounds the seeds. The non-cellulosic polysaccharides contained in this psyllium seed gum have a highly branched structure with a xylan main chain, and the side chains consist of arabinose, xylose, galacturonic acid, and rhamnose. Examples of commonly available products include Bistop® D-2074 manufactured by San-Ei Gen F.F.I. Co., Ltd.

[0026] Carrageenan is a natural polymer extracted and purified from the whole algae of the genera Hypnea, Eucheuma, Iridaea, Gigartina, and Chondrus. It contains sulfate groups and typically has a molecular weight of 100,000 to 1,500,000. Carrageenan is a polysaccharide composed of D-galactose and 3,6-anhydro-D-galactose. There are various types of carrageenan, including λ, ι, κ, μ, and ν, depending on the position of the sulfate groups in the basic structural unit of carrageenan and the presence or absence of anhydrosugars.

[0027] Gellan gum is a fermented polysaccharide produced by Pseudomonas elodea ATCC31461 or its mutant strains, and its constituent unit is a tetrasaccharide consisting of two D-glucose residues, one L-rhamnose residue, and one D-glucuronic acid residue. Gellan gum is broadly divided into native gellan gum obtained from the culture of the strain and deacylated gellan gum obtained by deacylation of native gellan gum.

[0028] Alginic acid is a polysaccharide extracted from seaweed, and its constituent sugars are β-D-mannuronic acid and α-L-guluronic acid. Salts of alginic acid include, but are not limited to, sodium alginate, potassium alginate, and ammonium alginate.

[0029] Xanthan gum is a fermented polysaccharide produced by Xanthomonas campestris. Xanthan gum is a polysaccharide with a β-1,4-D-glucan backbone, with side chains consisting of α-D-mannose, β-D-glucuronic acid, and β-D-mannose attached to every other glucose molecule in the backbone. The mannose attached to the backbone is acetylated at the C6 position, and the terminal mannose may be acetal-linked to pyruvic acid. The xanthan gum used in the present invention is not particularly limited; it may be xanthan gum with a lower than normal acetyl group content or no acetyl group, or xanthan gum with a lower than normal pyruvic acid content or no pyruvic acid.

[0030] The content of (A) gelling agent is not particularly limited and is adjusted appropriately depending on the type of (A) gelling agent and (B) nutritional component. From the viewpoint of significantly achieving the effects of the present invention, it is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more, based on the total amount of the jelly feed of the present invention. The content of (A) gelling agent is not particularly limited, but may be, for example, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less. From the viewpoint of significantly achieving the effects of the present invention, it is preferably 0.78% by mass or less.

[0031] (B) Nutritional Information (B) Nutritional components are not particularly limited as long as they do not impair the effects of the present invention. Examples include fish eggs (eggs of shark, red sea bream, eel, etc.), fish meal, fish protein hydrolysate, krill hydrolysate, and other aquatic organism-derived feed ingredients; oils and fats such as fish oil and cod liver oil; animal proteins such as casein (including salt), skim milk powder, whole eggs (e.g., chicken eggs), egg yolk, egg white, and albumin; vegetable proteins such as soybean peptides and soybean protein; amino acids such as taurine; and vitamins. These nutritional components may be used alone or in combination of two or more.

[0032] The jelly feed of the present invention preferably contains, as a nutritional component, one or more types selected from the group consisting of fish eggs and bird eggs, more preferably shark eggs, chicken eggs, or a combination thereof, and even more preferably spiny dogfish (Squalus suckleyi) eggs, chicken eggs, or a combination thereof.

[0033] The content of the (B) nutritional component is not particularly limited and can be adjusted appropriately depending on the type of (A) gelling agent and (B) nutritional component, but is preferably 2 to 99.99% by mass, more preferably 5 to 90% by mass, even more preferably 15 to 85% by mass, and particularly preferably 20 to 80% by mass, based on the total amount of the feed.

[0034] (Water content) The water content of the jelly feed of the present invention is not particularly limited, but is preferably, for example, 50 to 95% by mass.

[0035] (Load in indentation test / loss tangent (tanδ) in dynamic viscoelasticity test) The jelly feed of the present invention is preferably ingested by larval fish of the order Anguilliformes and has physical properties that inhibit diffusion in water. Therefore, it is necessary to adjust the load (normal force) measured by an indentation test to be in the range of 0.05 to 0.68 N, and the loss tangent (tanδ) measured by a dynamic viscoelasticity test to be in the range of 0.14 to 0.67.

[0036] The load in a compression test of the jelly feed of the present invention, when compressed to a strain of 1% at 20° C., is, from the viewpoint of suppressing diffusion of the feed, for example, 0.05 N or more, 0.06 N or more, 0.07 N or more, 0.08 N or more, 0.09 N or more, 0.1 N or more, 0.15 N or more, or 0.2 N or more. Furthermore, from the viewpoint of improving feeding ability, the load in a compression test is, when compressed to a strain of 1% at 20° C., for example, 0.68 N or less, 0.67 N or less, 0.66 N, 0.64 N or less, 0.62 N or less, 0.6 N or less, 0.55 N or less, or 0.50 N or less. The load can be measured under the compression test conditions described in the Examples.

[0037] The loss tangent (tanδ) in a dynamic viscoelasticity test of the jelly-like feed of the present invention is a parameter that can serve as an indicator of the fluidity of the gel. A gel (jelly) is generally defined as one whose loss tangent (tanδ) in a dynamic viscoelasticity test is 1 or less (Iijima et al., "Issues and Verifications Regarding the Scientific Evaluation of Shape Function in Semi-Solid Nutrition," Journal of the Japanese Society for Parenteral and Enteral Nutrition, Vol. 33, No. 1, pp. 595-601 (2018)). From the viewpoint of providing fluidity that allows larval fish to consume the jelly feed of the present invention, the loss tangent (tan δ) in a dynamic viscoelasticity test is, for example, 0.14 or more, 0.15 or more, 0.16 or more, 0.18 or more, 0.2 or more, 0.25 or more, or 0.3 or more at 20°C and a frequency of 1 Hz. Furthermore, the loss tangent (tan δ) in a dynamic viscoelasticity test is, for example, 0.67 or less, 0.66 or less, 0.64 or less, 0.62 or less, 0.6 or less, or 0.55 or less at 20°C and a frequency of 1 Hz. The loss tangent (tan δ) can be measured under the dynamic viscoelasticity test conditions described in the Examples.

[0038] (Embodiment: Feed containing bird or fish eggs) In a specific embodiment, (B) a feed using one or more components selected from the group consisting of fish and bird eggs as a nutritional component is mentioned. When shark eggs are used as a nutritional component, the shark eggs can be used without being diluted.

[0039] When psyllium seed gum is used as the (A) gelling agent, its content is, for example, 0.4 to 1.4% by mass, preferably 0.5 to 1.3% by mass, and more preferably 0.55 to 0.75% by mass, based on the total amount of the feed, from the viewpoint of significantly achieving the effects of the present invention. Here, when psyllium seed gum and κ-carrageenan are used in combination, the content of κ-carrageenan is, for example, 0.01 to 0.05% by mass, preferably 0.02 to 0.04% by mass, and more preferably 0.03% by mass, based on the total amount of the feed. (A) When ι-carrageenan is used as the gelling agent, its content is, for example, 0.07 to 0.15 mass%, preferably 0.09 to 0.13 mass%, and more preferably 0.10 to 0.12 mass% relative to the total amount of the feed, from the viewpoint of significantly achieving the effects of the present invention.

[0040] (A) When native gellan gum is used as the gelling agent, its content is, for example, 0.01 to 0.09% by mass, preferably 0.02 to 0.08% by mass, and more preferably 0.03 to 0.06% by mass relative to the total amount of the feed, from the viewpoint of significantly achieving the effects of the present invention. When sodium alginate is used as the (A) gelling agent, its content is, for example, 0.05 to 0.3% by mass, and preferably 0.1 to 0.2% by mass, relative to the total amount of the feed, from the viewpoint of significantly exhibiting the effects of the present invention.

[0041] 2. Method for producing jelly feed for eel larvae The jelly-like feed for eel larvae of the present invention can be obtained by adding water and other ingredients to (A) the gelling agent and (B) the nutritional components and mixing them according to a conventional method. The production method of the present invention preferably includes a heating step for dissolving (A) the gelling agent. The production method of the present invention may also include a sterilization step, a packaging step, a freezing step, etc. The produced jellied feed may be refrigerated or frozen.

[0042] 3. How to raise larval eels The method for rearing eel larvae of the present invention includes feeding the jelly-like feed for eel larvae of the present invention to the eel larvae. The rearing method of the present invention allows for artificial rearing of eel fish from the larval stage with reduced cost and effort. More specifically, the feed is prevented from dispersing in water, improving feeding efficiency (the ratio of ingested feed to fed feed), and also preventing contamination of the water and rearing system.

[0043] Although not particularly limited, it is preferable to raise and feed larvae in an aquarium. In such an environment where water exchange is limited, preventing deterioration of water quality is important in terms of reducing labor and costs, and therefore the rearing method of the present invention, which can prevent contamination of the water and rearing system, is particularly effective.

[0044] The number of times per day to feed is not particularly limited and can be changed as appropriate depending on the age of the fish being reared, but in the case of eel larvae, it is preferably 1 to 10 times per day, more preferably 5 times per day. The feeding of the feed preferably includes a step of feeding the feed in a state where the feed is localized in the aquaculture tank. The feeding method is not particularly limited, but examples include leaving the feed stationary on the water surface, underwater, or on the bottom of the aquarium, or placing the feed in a feed container, net, etc. and placing it on the water surface, underwater, or on the bottom of the aquarium, etc. [Example]

[0045] The present invention will be described in more detail below using examples, comparative examples, and test examples, but the present invention is not limited to these examples. In the examples, "parts" and "%" mean "parts by mass" and "% by mass," respectively.

[0046] [Indentation test] For the indentation test, a disposable parallel plate (50 mm diameter, D-PP50 / AL / S07, Anton Paar) was used as a measuring jig for a rheometer (MCR-302, Anton Paar) to measure the increase in load (normal force) when each of the feeds from the Examples and Comparative Examples was indented at a sample temperature of 20°C at a speed of 10 μm / s through a sample thickness (gap) of 1 mm, with a strain of 1% (10 μm).

[0047] [Dynamic viscoelasticity test] Dynamic viscoelasticity was measured using the same rheometer and jig as in the indentation test, with a sample temperature of 20°C, a sample thickness (gap) of 1 mm, a frequency of 1 Hz, and a strain range of 0.01% to 1000%, and the loss tangent (tanδ) was calculated.

[0048] [Evaluation of feeding habits] Each of the feeds of the Examples and Comparative Examples was fed to Japanese eel larvae at 25°C according to the following procedure, and feeding habits were evaluated. (1) Ten 100-day-old larvae were placed in a 10 L tank at 25°C, and feed was placed at the bottom of the tank. (2) 15 minutes after feeding, the amount of residue in the digestive tract of the larvae was observed. When observing the larvae, the entire body, including the esophagus, is transparent to light, so the ingested feed appears as a dark tubular image. The greater the amount of feed present in the esophagus, the greater the feed intake. Therefore, feeding ability was evaluated according to the following criteria. After observing the esophagus of each larvae that had received each feed, the feed that corresponded to the average condition of the larvae was evaluated as being unsuitable. Note that feeds rated x were evaluated as unsuitable as feed.

[0049] <Food intake criteria> ○: Continuous feed is visible in the esophagus. △: Feed is seen intermittently in the esophagus. ×: No feed was found in the esophagus.

[0050] [Evaluation of Diffusion] In the above-mentioned evaluation of feeding aptitude, the condition of the feed was visually observed 15 minutes after feeding, and the spreadability of the feed was evaluated according to the following criteria. Photographs of the reference feeds showing the following criteria are shown in Figure 1. <Standards for Diffusivity> ○: No significant breakdown of the feed at the bottom is observed and the rearing water is clear. △: Feed remains at the bottom, but some of it is distorted and the breeding water is cloudy. ×: No feed remains at the bottom and the rearing water is significantly cloudy.

[0051] Examples 1 to 8 and Comparative Examples 1 to 11 Preparation of Feed The feeds of Examples 1 to 8 and Comparative Examples 1 to 11 were prepared according to the following preparation procedures. (1) The raw materials listed in Table 1 (except for ion-exchanged water and cod liver oil) were mixed in advance, and then cod liver oil and ion-exchanged water were added and stirred at room temperature to prepare slurries of three types of nutritional components (abbreviated as fish meal 1, fish meal 2, and shark roe, respectively). (Comparative Examples 1 to 3: The above-mentioned slurries of nutrients were used as feed as they were.) (2) To ion-exchanged water in an amount equal to 1 / 4 of the amount of the slurry obtained in (1) (Examples 5 and 6), or to ion-exchanged water in an amount equal to the amount of the slurry obtained in (1) (Comparative Examples 4 to 11, Examples 1 to 4, 7 and 8), a gelling agent was added to give a mass % as shown in Table 2, and the mixture was stirred at 80°C for 10 minutes to dissolve, thereby obtaining a gelling agent solution. (3) The slurry obtained in (1) was gradually added to the gelling agent solution obtained in (2), and the mixture was stirred and mixed while heating to 80°C to obtain a feed. The feeds of Comparative Examples 6 and 8 were frozen and then thawed before use. The feeds for rheometer measurement were filled into a disposable bottom dish (EMS / CTD600, manufactured by Anton Paar) to a sample thickness of 1 mm and refrigerated.

[0052] [Table 1]

[0053] [Table 2]

[0054] The gelling agents used in Table 2 are as follows: Psyllium seed gum: Bistop (registered trademark) D-2074 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) κ-Carrageenan: Carrageenan CS-530 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) Io-carrageenan: Sun Support (registered trademark) P-90 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) Native gellan gum: Kelcogel LT100 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) Sodium alginate: Sunsupport (registered trademark) P-80 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) Xanthan gum: San-Ace (registered trademark) (manufactured by San-Ei Gen F.F.I. Co., Ltd.) Agar: Sansupport (registered trademark) P-60 (manufactured by San-Ei Gen F.F.I. Co., Ltd.) CMC-Na (Carboxycellulose sodium): Bistop® D-2208 (manufactured by San-Ei Gen F.F.I. Co., Ltd.)

[0055] Test Example 1: Indentation test, dynamic viscoelasticity test, evaluation of intake and diffusibility The feeds of Examples 1 to 8 and Comparative Examples 1 to 11 were subjected to a compression test, a dynamic viscoelasticity test, and evaluations of intake and diffusibility. The evaluation results are shown in Table 3.

[0056] [Table 3]

[0057] As can be seen from Table 3, the load in the indentation test for each of the feeds of Examples 1 to 8 was 0.05 to 0.64 N, and the loss tangent (tanδ) in the dynamic viscoelasticity test was 0.22 to 0.66. Each of the feeds of Examples 1 to 8 was excellent in both intake and diffusibility. As described above, it can be seen that the jelly feed of the present invention solves the problems of the present invention.

[0058] The effects of the present invention, ie, feeding ability and diffusibility, will be discussed below from the viewpoints of "load in an indentation test" and "loss tangent (tan δ) in a dynamic viscoelasticity test." (1) Feeding habits In terms of the "load in the indentation test," with the exception of Comparative Example 5, when the load was 0.01 to 0.64 N (Examples 1 to 8 and Comparative Examples 1 to 4 and 11), the feeding ability was rated as good or fair, and the larval fish were able to feed favorably. In contrast, when the load was 0.69 to 1.00 N (Comparative Examples 6 to 8), the feeding ability was rated as bad, and the larval fish were unable to feed. Therefore, for feeding ability, a load of 0.68 N or less is required.

[0059] In terms of "loss tangent (tanδ) in dynamic viscoelasticity testing," when the loss tangent (tanδ) is 0.22 to 3.75 (Examples 1 to 8 and Comparative Examples 1 to 4 and 11), feeding ability is rated as good or fair, and the larvae feed favorably. In contrast, when the loss tangent (tanδ) is 0.13 (Comparative Example 5), feeding ability is rated as bad, and feeding by the larvae is impaired. Therefore, for feeding ability, a loss tangent (tanδ) of 0.14 or higher is required.

[0060] In this test, eel larvae were observed plunging their heads into the feed and sucking it up. The results in Table 3 above show that this feeding pattern requires both an "indentation hardness" that allows the larvae to plunging their heads in and an appropriate "dynamic viscoelasticity" that facilitates inhalation. For example, the feeds of Comparative Examples 6 to 8, which had an "indentation test load" of 0.69 to 1.00 N, were too hard for the eel larvae to plunging their heads into the feed, presumably impairing their feeding ability.

[0061] (2) Diffusibility In terms of the "load in the indentation test," when the load was 0.05 to 1.00 N (Examples 1 to 8 and Comparative Examples 5 to 8), the diffusibility was rated as ○ or △, and diffusion was suppressed. In contrast, when the load was 0.01 to 0.04 N (Comparative Examples 1 to 4 and 9 to 11), the fluidity was high and a stable jelly was not formed. Therefore, the diffusibility was rated as ×, and the feed diffused. Therefore, a load of 0.05 N or more is necessary for diffusibility.

[0062] In terms of the "loss tangent (tanδ) in the dynamic viscoelasticity test," when the loss tangent (tanδ) was 0.13 to 0.69 (Examples 1 to 8 and Comparative Examples 5 to 8), the diffusibility was rated as ○ or △, and diffusion was suppressed. In contrast, when the loss tangent (tanδ) was 0.70 to 3.75 (Comparative Examples 1 to 4 and 11), the fluidity was high and a stable jelly was not formed. Therefore, the diffusibility was rated as ×, and the feed diffused. Therefore, for diffusibility, the loss tangent (tanδ) needs to be 0.69 or less.

[0063] As described above, in order to improve the feeding ability of jelly feed for larval fish of the order Anguilliformes and to suppress diffusion in rearing water, it is preferable that the "load in the indentation test" be 0.05 to 0.68 N and the "loss tangent (tan δ) in the dynamic viscoelasticity test" be 0.14 to 0.67. Furthermore, according to the results in Table 3, the "load in the indentation test" is preferably 0.05 to 0.60 N, more preferably 0.09 to 0.55 N, and even more preferably 0.15 to 0.50 N. Furthermore, the loss tangent (tan δ) in the dynamic viscoelasticity test is preferably 0.20 to 0.67, more preferably 0.22 to 0.66, and even more preferably 0.24 to 0.66.

[0064] The feeds of Comparative Examples 6 and 8 were frozen and then thawed. The load in the compression test was larger than that of the non-frozen feed. The feeds of Examples 1 to 8 were all uniform in content with no irregularities.

[0065] Test Example 2: Evaluation of stability during refrigerated storage For Example 5 and Comparative Examples 4, 5, 7, 9, and 10, the gelling agent and nutritional components were mixed and refrigerated at 4°C for one day. The state of the feed after refrigeration is shown in Figure 2. In Comparative Examples 9 and 10, which used CMC-Na as the gelling agent, aggregation and precipitation of the nutritional components were observed. This separation leads to non-uniformity of the nutritional components within the feed, so feed using CMC-Na is not preferable from the perspective of stability during refrigerated storage. In the other examples, Example 5, Comparative Examples 4, 5, and 7, this phenomenon was not observed.

[0066] Test Example 3: Evaluation of diffusibility using equipment Diffusivity was evaluated using a dissolution tester (PJ-32S, Miyamoto Riken Kogyo Co., Ltd.) 3 mL of feed was placed at the bottom of a special vessel containing 900 mL of artificial seawater prepared by dissolving marine salt (Kaisui Marine) in ion-exchanged water, and the water was stirred at 40 rpm for 15 minutes using a special paddle shaft. The water was then sampled and the transmittance at 720 nm was measured using a spectrophotometer (V-560, JASCO Corporation).

[0067] Figure 3 shows the relationship between the "load in the indentation test" and the "loss tangent (tanδ) in the dynamic viscoelasticity test" of the feeds of Example 5 and Comparative Examples 4, 5, 7, and 9 and their diffusibility in the rearing water, as measured using a dissolution tester. When the "load in the indentation test" was large (0.68 N or more), the effect of inhibiting diffusion was greater, and turbidity of the rearing water was suppressed. When the "load in the indentation test" was small (0.03 N or less), the feed rapidly diffused into the water, causing the rearing water to become turbid.

[0068] When the "loss tangent (tanδ) in the dynamic viscoelasticity test" was small (0.14 or less), the gel had low fluidity and did not diffuse at all when the load was large (0.68 N or more), but when the load was smaller (0.03 to 0.68 N), the gel diffused as a fine, hard, granular gel.When the "loss tangent (tanδ) in the dynamic viscoelasticity test" was large (0.70 or more), the gel had high fluidity and the feed diffused rapidly into the water, causing the rearing water to become suspended. [Industrial Applicability]

[0069] The present invention provides a method for rearing eel larvae at low cost, and also provides an inexpensive feed that is inhibited from spreading in rearing water and that is preferred by eel larvae.

Claims

1. A jelly-like feed for larval eels of the order Anguilliformes, comprising (A) a gelling agent and (B) a nutritional component, In a compression test, the load when the feed was compressed by 1% strain at 20°C was 0.05 to 0.68 N, A jelly-like feed in which the loss tangent (tan δ) of the feed at 20°C and a frequency of 1 Hz is 0.14 to 0.67 in a dynamic viscoelasticity test.

2. 2. The jelly-like feed according to claim 1, wherein the gelling agent (A) is one or more selected from the group consisting of psyllium seed gum, xanthan gum, gellan gum, carrageenan, alginic acid, hyaluronic acid, chondroitin sulfate, fucoidan, pectin, soybean polysaccharides, welan gum, carboxymethyl starch, phosphorylated starch, phosphate cross-linked starch, starch octenyl succinate, starch acetate, and salts thereof.

3. The jelly feed according to claim 1 or 2, wherein the nutritional component (B) comprises sodium caseinate.

4. A method for raising eel larvae, comprising a step of feeding the jelly feed according to any one of claims 1 to 3 to the eel larvae.

5. The method according to claim 4, wherein the larvae of the order Anguilliformes are reared in a closed circulation tank.

Images