Larval-fish feed, method for producing same, method for rearing fish, and method for using feed

Abstract

Provided are a larval-fish feed with which it is possible to promote growth by improving the survival rate of larval fish, and a method for rearing fish. A larval-fish feed (40) comprises a body portion (10) configured from a fish-derived-component-containing formulation, and a gel-like coating portion (20) covering the body portion (10). This method for rearing fish includes a first step for feeding a biological bait to a larval fish, and a second step for feeding a larval-fish feed (40) to the larval fish, the second step being started after the start of the first step.

Description

Larval feed and its manufacturing method, fish breeding method, and method of using feed

[0001] The present disclosure relates to larval fish feed and methods for producing the same, methods for raising fish, and methods for using the feed.

[0002] In order to protect wild fish resources, efforts are being made to restrict catches of some fish species. In order to respond to these efforts, it is hoped that a cycle can be realized in which artificially hatched fry are raised to adulthood, and then eggs are obtained by the adult fish spawning, thereby protecting resources and ensuring a stable supply. In order to efficiently advance this cycle, it is necessary to establish technology to improve the survival rate of fish species that have problems with their survival rate to adulthood.

[0003] For example, Patent Document 1 studies how to improve the survival rate of juvenile fish by adding a fish-derived phospholipid fraction to feed, while Patent Document 2 studies how to improve the survival rate of juvenile bluefin tuna by adding a gelling agent to fish feed ingredients to make the compound feed gummy.

[0004] JP 2013-59293 A JP 2011-206052 A

[0005] However, the survival rate of larvae remains low, and further improvements are necessary to ensure stable larval growth. The inventors' studies have revealed that larval death occurs frequently when switching from live feed to formulated feed, and that this is one of the factors behind the low survival rate of larvae. Therefore, the present disclosure provides larval feed and a method for producing the same, which can improve the survival rate of larvae and promote their growth by increasing the feeding rate of larvae when switching from live feed to formulated feed. The present disclosure also provides a fish rearing method that can improve the survival rate of larvae and promote their growth.

[0006] One aspect of the present disclosure provides larval fish feed comprising a main body made of a compound containing fish-derived ingredients and a gel-like coating covering the main body. This larval fish feed comprises a gel-like coating covering the main body made of a compound containing fish-derived ingredients. This improves the feed's swallowability. It also makes the appearance of the larval fish feed more similar to live feed. As a result, it is presumed that the feeding rate increases when switching from live feed to compound feed, suppressing starvation and the resulting cannibalism. This improves the survival rate of larval fish and promotes their growth.

[0007] The diameter of the main body, when converted into a sphere of the same volume, may be 0.25 to 5 mm. Larvae generally have poorer eyesight than adult fish, so if the size of the feed is too small, it tends to be difficult for them to eat the food. On the other hand, if the size of the feed is too large, it tends to be difficult for the larvae to pass through their pharynx. Therefore, larvae feed having the above-mentioned size can facilitate larval eating while also improving swallowability.

[0008] The larval feed may contain a feeding promoter, which can further increase the feeding rate. The feeding promoter may be contained in the main body or the covering.

[0009] The settling velocity in seawater may be less than 3.5 cm / sec. A settling velocity within this range can promote predation by larval fish. This prevents the accumulation of feed that is not consumed by larval fish at the bottom of the aquarium, etc., and reduces the frequency of cleaning the aquarium, etc.

[0010] The salinity of the water contained in the main body may be lower than that of seawater. The larval fish feed has a covering portion, which prevents the main body from coming into direct contact with seawater. This allows the salinity of the water contained in the main body to be maintained lower than that of seawater. The digestibility of such larval fish feed is significantly better than that of feed containing water with a salinity equivalent to that of seawater.

[0011] The larvae may belong to the order Perciformes. Larvae of Perciformes tend to consume feed that is relatively large compared to the size of their esophagus. Therefore, by feeding the larvae feed with improved swallowability, the survival rate can be significantly improved.

[0012] The weight ratio of the covering portion to the main body portion may be 1 to 20% by weight, which allows the tablet to contain sufficient nutrients while also improving ease of swallowing.

[0013] Another aspect of the present disclosure provides a method for raising fish, comprising a first step of feeding live feed to larvae, and a second step of feeding the larvae with any of the larvae feeds described above after the first step, in which the second step begins after the first step begins.

[0014] Larvae tend to have a low feeding rate when switching from live feed to compound feed. In the rearing method described above, feeding the larvae feed described above can improve the swallowability of the feed. Furthermore, the appearance of the larvae feed can be made more similar to that of live feed. As a result, it is presumed that the feeding rate at the above timing is high, and starvation and the resulting cannibalism are suppressed. Therefore, the mortality rate of larvae is suppressed, and the survival rate of larvae is improved, promoting growth.

[0015] Another aspect of the present disclosure provides a method for raising fish, comprising a first step of feeding live feed to larvae and a second step of feeding the larvae any of the above-described larval feeds. It is believed that this rearing method also maintains a high feeding rate and suppresses starvation and the resulting cannibalism. Therefore, the mortality rate of larvae is suppressed, improving the survival rate of larvae and promoting their growth. From a similar perspective, the second step may be started after the first step is completed.

[0016] In the rearing method, it is not necessary to feed the larvae with hatched larvae. In the rearing method, for example, it is not necessary to feed the larvae with hatched larvae at least in the first and second steps, and it is not necessary to feed the larvae with hatched larvae throughout the rearing period. In the rearing method, by feeding the larvae feed described above, the feeding rate can be increased, so the larvae can ingest sufficient nutrients even without feeding them with hatched larvae.

[0017] The second step may be initiated when the larvae are 10 to 30 days old. Conventionally, this period includes the timing of switching from live feed to formulated feed, and therefore the feeding rate tends to be low. However, by using the above-mentioned formulated feed, the feeding rate during this period can be sufficiently increased. Note that, in the present disclosure, the day of hatching is counted as day 0. In other words, the day after hatching is considered to be 1 day old, and the day after that is considered to be 2 days old.

[0018] Yet another aspect of the present disclosure provides a method for producing larval fish feed, comprising the steps of adhering a gel-like component to the surface of a main body composed of a compound containing fish-derived components and coating the surface of the main body with a gel-like coating. This significantly improves the swallowability of the feed for larval fish. It also makes the appearance of the larval fish feed more similar to live feed. This is thought to increase the feeding rate at the time of switching from live feed to compound feed, thereby suppressing starvation and the resulting cannibalism. This, in turn, improves the survival rate of larval fish and promotes their growth.

[0019] Yet another aspect of the present disclosure provides a method for using a feed comprising a main body composed of a compound containing fish-derived components and a gel-like coating covering the main body for raising larval fish. Any of the larval feeds described above can be used as the feed. This method of use can improve the swallowability of the feed. It can also make the appearance of the larval feed more similar to live feed. As a result, it is presumed that the feeding rate increases when switching from live feed to compound feed, suppressing starvation and the resulting cannibalism. This can improve the survival rate of larval fish and promote their growth.

[0020] According to the present disclosure, it is possible to provide larval feed capable of improving the survival rate of larval fish and promoting their growth, and a method for producing the same. The present disclosure also provides a fish rearing method capable of improving the survival rate of larval fish and promoting their growth. The present disclosure also provides a method for using the feed capable of improving the survival rate of larval fish and promoting their growth.

[0021] 1 is a schematic cross-sectional view of the larval feed; 2 is a photograph showing an example of an observation image of the larval feed of Example 1 using a stereomicroscope; 3 is a photograph showing an example of an observation image of the larval feed of Comparative Example 1 using a stereomicroscope;

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings as needed. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. In the description, the same elements or elements having the same functions will be designated by the same reference numerals, and redundant explanations will be omitted where appropriate. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of each element are not limited to those shown in the drawings.

[0023] 1 is a schematic cross-sectional view of a larval fish feed 40 comprising a main body 10 made of a compound containing fish-derived ingredients and a gel-like coating 20 that coats the main body 10. Larval fish in this disclosure are fish that are, for example, 10 to 40 days old after hatching. This period includes the timing of switching from live feed to compound feed. The size of larval fish varies depending on the fish species, but for example, it is 5 to 100 mm for bluefin tuna and 5 to 70 mm for yellowtail.

[0024] The species of the larvae is not particularly limited and may be, for example, Perciformes. The fish species may be Carangidae, Scombridae, or Crayfish. The fish species may be Tuna, Seriola, Spanish mackerel, or Scombridae. More specifically, the fish include the red seabream (Doederleinia berycoides), yellowtail (Seriola quinqueradiata), amberjack (Seriola dumerili), long-fin amberjack (Seriola rivoliana), amberjack (Seriola lalandi), striped jack (Pseudocaranx dentex), bluefin tuna (Thunnus orientalis), Atlantic bluefin tuna (Thunnus thynnus), southern bluefin tuna (Thunnus maccoyii), bigeye tuna (Thunnus obesus), yellowfin tuna (Thunnus albacares), albacore tuna (Thunnus alalunga), skipjack tuna (Katsuwonus pelamis), flathead sow (Auxis thazard), roundfin tuna (Auxis rochei), spotted spotted amberjack (Euthynnus affinis), swordfish (Xiphias gladius), and marlin (Kajikia Examples include Japanese horse mackerel (Trachurus japonicus), Spanish mackerel (Scomberomorus niphonius), Japanese mackerel (Scomber japonicus), Japanese sea bass (Lateolabrax japonicus), and red sea bream (Pagrus major). Among these, particularly, yellowtail (Seriola quinqueradiata), amberjack (Seriola dumerili), yellowtail amberjack (Seriola lalandi), striped jack (Pseudocaranx dentex), bluefin tuna (Thunnus orientalis), Atlantic bluefin tuna (Thunnus thynnus), and southern bluefin tuna (Thunnus maccoyii) may be used. Larvae of these fish species may consume feed that is relatively large compared to the size of their esophagus. Therefore, by providing the larval feed 40 with a gel-like coating 20, the resistance to the movement of the larval feed 40 in the pharynx and esophagus of the larval fish is reduced, improving swallowability.

[0025] The compound constituting the main body 10 may contain water and fish-derived ingredients such as fish meal or fish oil. The main body 10 may contain ingredients other than the fish-derived ingredients and water. Examples of such ingredients include starches, glutens, cellulose, soy protein, vitamins, minerals, and antioxidants. Crystals of fish meal and minerals are hard and tend to damage the pharynx and other parts of the larvae. Because the larvae feed 40 includes the coating 20, it is possible to increase the feeding rate even if the main body 10 contains hard ingredients.

[0026] It is preferable that the main body 10 does not contain the gel-like component that constitutes the covering 20. This not only increases the nutrient content of the larval feed 40 but also improves digestibility for larval fish whose internal organs are not yet mature, further improving survival rates and promoting growth. Furthermore, by including a large amount of oil components in the main body 10, which are not normally contained in large amounts in gel-like components, the growth of larval fish can be further promoted.

[0027] The larval fish feed 40 may contain a feeding enhancer. The feeding enhancer may be contained in the main body 10, the covering 20, or both. If the covering 20 contains a feeding enhancer, the feeding enhancer will quickly dissolve in the water when the larval fish feed 40 comes into direct contact with the surrounding water, making it more easily detected by the larval fish. From this perspective, it is more preferable that the feeding enhancer be contained in the covering 20. From the perspective of efficiently exerting the feeding enhancement function and reducing manufacturing costs, it is preferable that the feeding enhancer be contained in the covering 20 but not in the main body 10. The feeding enhancer may be an amino acid such as alanine, lysine, glutamic acid, or histidine, or may be inosinic acid. It may also be krill extract or seafood extract. The inclusion of a feeding enhancer can further increase the feeding rate. The larval fish feed 40 may be colored by including a colorant in the main body 10, the covering 20, or both. The color can be appropriately selected by considering the feeding enhancement effect for each target fish species.

[0028] The salinity of the water contained in the main body 10 may be lower than that of seawater (24°C), for example, 0.02% by weight or less, or even 0.01% by weight or less. By lowering the salinity in this manner, the digestibility of the larval fish feed can be improved. The salinity of the water contained in the main body 10 is measured using a commercially available salinity meter after the main body 10 is mixed and stirred in distilled water to obtain a dispersion, and then the solids are removed from the dispersion to obtain a solvent. The salinity of the water contained in the main body 10 can be calculated based on this measurement value.

[0029] The diameter of the main body 10 (2 × r １ ) may be 0.25 to 5 mm, 0.3 to 3 mm, or 0.4 to 1 mm. Larval feed having such a size can be easily eaten by larval fish and can have better swallowability.

[0030] Diameter of the larval fish feed 40 (2 × r ２ The thickness of the covering portion 20 may be 0.03 to 1 mm, 0.05 to 0.4 mm, or 0.1 to 0.3 mm.

[0031] The shape of the larvae feed 40 may be a sphere whose cross section passing through the center P is circular as shown in FIG. 1, or may be a shape different from a sphere. For example, the cross section may be flattened to be elliptical, or may have irregularities so that the cross section is polygonal. In other words, the larvae feed 40 may have irregularities on its surface. In such a case, the diameter (2×r １ ) and the diameter of the larval feed (2 × r ２ ) can be calculated by converting the main body 10 and the larval fish feed 40 into spheres of the same volume.

[0032] It is preferable, but not limited to, that the entire surface of the main body 10 be covered with the covering portion 20. For example, a portion of the surface of the main body 10 may be exposed to the outside. However, it is preferable that 80% or more, and preferably 90% or more of the entire surface of the main body 10 be covered with the covering portion 20.

[0033] The weight ratio of the covering portion 20 to the main body portion 10 may be 1 to 20% by weight, 1.5 to 18% by weight, or 2 to 16% by weight. By setting the weight ratio of the main body portion 10 to the covering portion 20 within this range, it is possible to sufficiently improve swallowability while containing sufficient nutrients.

[0034] The gel-like coating 20 has viscosity, which prevents injury to the pharynx of the larvae. Examples of gel-like components constituting the coating 20 include gelatin, collagen, alginic acid, hyaluronic acid, agar, guar gum, carrageenan, pectin, xanthan gum, gum arabic, gellan gum, locust bean gum, pullulan, soybean polysaccharides, tamarind gum, and psyllium. The gel-like components may be used alone or in combination. The coating 20 composed of such gel-like components may typically be transparent or translucent. The inclusion of such a gel-like coating 20 provides an appearance similar to live feed, which is thought to visually promote feeding by larvae. This may accelerate the onset of feeding. In this disclosure, "transparent" refers to the fact that the main body 10 can be completely seen through the larvae feed 40 when viewed visually. In the present disclosure, "semi-transparent" means that when the larval fish feed 40 is visually inspected, it is possible to distinguish that there is something different inside (main body portion 10) from the covering portion 20.

[0035] From the viewpoint of suppressing exposure of the main body 10, it is preferable that the gel component be insoluble or poorly soluble in seawater at 30°C. From the same viewpoint, the gel component may be a solid that does not have fluidity. With such a gel component, after the larval fish feed 40 is introduced into seawater, a high proportion of the larval fish feed 40 is ingested before all of the gel component dissolves. This increases the feeding rate and further improves the swallowability of the feed.

[0036] When the gel-like component is gelatin, gelatin derived from animals can be used. Examples of animal-derived gelatin include fish-, bovine-, porcine-, and avian-derived gelatin. Among these, bovine-, porcine-, or avian-derived gelatin is preferred because a gel-like component with a low melting point tends to cause the covering portion 20 to peel or fall off easily in water. Of these multiple types of gelatin derived from different origins, any one type may be used alone, or multiple types may be used in combination.

[0037] The settling velocity of the larval fish feed 40 in seawater may be less than 3.5 cm / sec, or even less than 3.0 cm / sec. A settling velocity within this range can promote predation by the larval fish. This prevents the feed that is not consumed by the larval fish from accumulating at the bottom, reducing the frequency of cleaning the aquarium.

[0038] An example of a method for manufacturing the larval fish feed 40 is described below. The manufacturing method of this example includes a step of attaching a gel-like component to the surface of a main body portion composed of a compound containing fish-derived components, and then coating the surface of the main body portion with a gel-like coating. The compound can be obtained by blending the fish-derived components contained in the main body portion 10 described above and, if necessary, the other components described above. A mixed liquid containing the gel-like component is attached to the surface of the obtained compound. The attachment of the gel-like component to the surface of the main body portion may be performed in one step or in multiple steps.

[0039] The mixed liquid may be prepared by heating to improve the fluidity and the solubility of the gel-like component. A feeding promoter may be added to the mixed liquid. The mixed liquid may be applied to the surface of the formulation by, for example, spraying the mixed liquid containing the gel-like component onto the surface of the formulation, or by immersion. Of these, spraying the mixed liquid is preferred from the viewpoint of making it easier to adjust the degree of coverage. After the mixed liquid containing the gel-like component is applied to the surface of the formulation, the gel-like component is solidified to form a coating portion 20 made of the gel-like component on the surface of the main body portion 10 made of the formulation.

[0040] When the gel component is applied to the surface of the main body 10 in multiple steps, the coating portion formed by the above procedure may serve as the base layer. In this case, the mixed liquid containing the gel component is again applied to the surface after the base layer has been formed. This may also be done, for example, by spraying the mixed liquid containing the gel component onto the surface of the base layer. The gel component is then solidified to form a surface layer on the base layer. This results in the main body 10 composed of the compound and the gel-like coating portion 20 covering the main body 10. The mixed liquid used to form the base layer and the surface layer may be the same, or may be mixed liquids containing different gel components. Furthermore, the mixed liquids may have different concentrations of the gel components. Immersion in the mixed liquid and spraying may also be performed in combination. While the order of these steps is not particularly limited, immersion followed by spraying is preferred from the perspective of making it easier to adjust the degree of coating. The concentrations and components of the mixed liquids used for immersion and spraying may be different from each other.

[0041] In this way, it is possible to manufacture the larval fish feed 40 having the main body portion 10 and the covering portion 20. However, the manufacturing method of the larval fish feed 40 is not limited to the above. For example, the attachment of the gel-like component may be carried out in three or more steps.

[0042] The larval feed 40 includes a gel-like covering 20 that covers a main body 10 composed of a compound containing fish-derived ingredients. This improves the swallowability of the feed. It also makes the appearance of the larval feed closer to that of live feed. As a result, it is believed that the feeding rate increases when switching from live feed to compound feed, improving the survival rate of larval fish. Larval feed 40 is suitable for use in rearing or culturing larval fish. Larval feed 40 is also suitable for use in rearing larval fish.

[0043] Next, an example of a method for raising fish using larval feed 40 will be described. The raising method of this example includes a first step of feeding live feed to larval fish, and a second step of feeding the larval feed 40 after the first step. In the first step, live feed such as Artemia and rotifers is fed to newly hatched larval fish. After the first step, the second step of feeding the larval fish with the larval feed 40 is started. The second step may be started after the first step is completed, or the first step may be completed after the second step is started, so that part of the first step and part of the second step can be carried out in parallel.

[0044] The second step may be initiated when switching from live feed to formulated feed. The second step may be initiated after hatching, for example, between 10 and 30 days of age. In the second step, since the larvae feed 40 is fed, a high feeding rate can be maintained when transitioning from live feed to formulated feed. This suppresses death due to starvation and cannibalism, and increases survival rate and growth potential. The second step may be initiated after hatching, for example, between 10 and 20 days of age. This improves the feeding rate during a period when feeding is difficult. From the viewpoint of achieving both a high level of survival rate and growth potential, the size of the larvae feed 40 in the second step may be gradually increased as the larvae age increases.

[0045] For example, in the case of bluefin tuna and Spanish mackerel, which have strong piscivorous tendencies, hatched larvae are sometimes fed to produce seedlings. Suitable hatched larvae are fish species that spawn continuously and in large quantities according to the production season. Examples of such fish species include the spotted rockfish and the yellowfin tuna. However, in this case, in addition to producing farmed fish, spawning parent fish must be continuously reared year-round, with water temperature and photoperiods appropriately controlled to ensure spawning. This requires large aquariums for the parent fish, and significant labor and cost are required for managing the fertilized eggs and feeding the hatched larvae. Furthermore, when hatched larvae are used as feed, there is a risk of infectious diseases transmitted through the hatched larvae compared to compound feed produced through a heating process. Therefore, the rearing method of this example makes it possible to rear fish without feeding hatched larvae to larvae, thereby reducing rearing costs and the risk of infectious diseases. Fish may be farmed using this rearing method. This reduces farming costs and enables efficient production of adult fish.

[0046] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. For example, the larval fish feed 40 may have a portion between the main body portion 10 and the covering portion 20 that is made of a different composition from the main body portion 10 and the covering portion 20.

[0047] The above-described embodiments include the following [1] to

[15] . [1] Larvae feed comprising a main body made of a compound containing a fish-derived component and a gel-like coating covering the main body. [2] The larvae feed according to [1], wherein the main body has a diameter of 0.25 to 5 mm when converted into a sphere of the same volume. [3] The larvae feed according to [1] or [2], which contains a feeding enhancer. [4] The larvae feed according to any one of [1] to [3], wherein the sedimentation velocity in seawater is less than 3.5 cm / sec. [5] The larvae feed according to any one of [1] to [4], wherein the salinity of the water contained in the main body is lower than that of seawater. [6] The larvae feed according to any one of [1] to [5], wherein the larvae belong to the order Perciformes. [7] The larvae feed according to any one of [1] to [6], wherein the weight ratio of the coating to the main body is 1 to 20% by weight. [8] A method for raising fish, comprising a first step of feeding live feed to larvae, and a second step of feeding the larvae feed described in any one of [1] to [7], wherein the second step is started after the first step has started. [9] The method for raising fish described in [8], wherein the second step is started after the first step has ended.

[10] The method for raising fish described in [8] or [9], wherein hatched larvae are not fed.

[11] The method for raising fish described in any one of [8] to

[10] , wherein the second step is started when the larvae are 10 to 30 days old.

[12] A method for producing larval feed, comprising a step of attaching a gel-like component to the surface of a main body made of a compound containing a fish-derived component, and coating the surface of the main body with a gel-like coating.

[13] A method for using feed, comprising a main body made of a compound containing a fish-derived component and a gel-like coating that covers the main body, for raising larvae.

[14] The method for producing larval feed according to

[12] , wherein the larval feed is the larval feed according to any one of [2] to [7].

[15] The method for using the feed according to

[13] , wherein the larval feed is the larval feed according to any one of [2] to [7].

[0048] The present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0049] Larval Feed Preparation 1 Example 1 Commercially available granular gelatin (bovine-derived, product name: Cook Gelatin, manufactured by Morinaga & Co., Ltd.) was mixed with distilled water to a gelatin concentration of 10% by weight and heated in a microwave oven until the granules disappeared, producing a gelatin solution in which the gelatin was dissolved in water. 100 g of commercially available mixed feed (tuna heart, manufactured by Nisshin Marubeni Feed Co., Ltd.) was spread on a mesh screen, and approximately 15 ml of the gelatin solution was sprayed onto the mixed feed using a spray bottle. After allowing it to cool at room temperature for at least 30 minutes, the mixed feed was again sprayed with approximately 15 ml of the gelatin solution. After spraying, it was again allowed to cool at room temperature for at least 30 minutes. The resulting gelatin-coated feed, with gelatin adhering to the surface, was designated the larval feed of Example 1. The weight of this larval feed increased by approximately 7 to 16% by weight compared to the mixed feed before gelatin coating.

[0050] A glass petri dish was filled with water, and the larval feed of Example 1 was observed therein using a stereomicroscope. Figure 2 is a photograph showing an example of an image of the larval feed of Example 1 observed using a stereomicroscope. As shown in the photograph in Figure 2, it was confirmed that in the larval feed (gelatin-coated feed), a coating portion containing gelatin (gelatin film) was formed around the main body portion composed of the compound feed. In larval feed with such a structure, the diameter of the main body portion composed of the compound feed was approximately 0.4 to 1.0 mm when converted into a sphere of the same volume.

[0051] The sedimentation rate of the larval fish feed of Example 1 in seawater was measured using the following procedure. Specifically, seawater was poured into a cylindrical transparent acrylic pipe with a diameter of 5 cm, which had been filled to a depth of 70 cm. The larval fish feed was dropped from a height of 15 cm relative to the seawater surface in the acrylic pipe. The time required for the dropped larval fish feed to sink vertically downward to 70 cm after starting to sink into the seawater was measured, and the sedimentation rate was calculated. The resulting sedimentation rate was 0.4 to 3.5 cm / sec.

[0052] (Example 2) A feeding enhancer was mixed at a concentration of 0.1 g / mL with a gelatin solution prepared in the same manner as in Example 1. Larval feed was prepared in the same manner as in Example 1, except that a gelatin solution containing such a feeding enhancer was used.

[0053] (Comparative Example 1) The commercially available compound feed (main body only) used in Example 1 was used as the larval feed of Comparative Example 1. Figure 3 is a photograph showing an example of an observation image of the larval feed of Comparative Example 1 using a stereomicroscope. As shown in the photograph in Figure 3, it was confirmed that no gelatin film was formed in the larval feed of Comparative Example 1.

[0054] [Feeding Ability Evaluation 1] Feeding ability was evaluated using the larval feeds prepared in Example 1 and Comparative Example 1. Specifically, approximately 100 27-day-old bluefin tuna larvae (total length approximately 20 mm) hatched at the Oita Marine Research Center were housed in a 1-ton tank and fed the larval feed of Example 1 or Comparative Example 1, and the swallowing ratio (= number of swallowed tails / number of spit out tails) during feeding was measured. For the measurement, the larval feed of Example 1 and the larval feed of Comparative Example 1 (approximately 1 g) were fed alternately 11 times, and the number of swallowed tails and the number of spit out tails were counted visually.

[0055] The results are shown in Table 1. As shown in Table 1, by providing a coating portion containing gelatin (gelatin film), the swallowing ratio increased by about 5.5 times.

[0056]

[0057] [Evaluation of Changes in Feeding Rate 1] Changes in feeding rate were evaluated using the larval fish feeds of Examples 1 and 2 and Comparative Example 1 and bluefin tuna larvae hatched at the Oita Marine Research Center. In the following evaluation, the water supply was three rotations per day. In addition to the compound feeds of each Example and Comparative Example, S-type rotifers enriched with Hypergloss (Marine Tech Co., Ltd.) and North American Artemia enriched with Super Marine Gross (Marine Tech Co., Ltd.) were used as feed. To maintain the aquarium environment and provide food for the S-type rotifers, a total of 60 mL / day of Marine Fresh (Marine Tech Co., Ltd.) and High-Grade Raw Chlorella V-12 (Chlorella Kogyo Co., Ltd.) were added in 5 to 6 doses.

[0058] Coating area A (two 1-ton black polycarbonate tanks), coating area B (one 1-ton black polycarbonate tank), and control area (two 1-ton black polycarbonate tanks) were prepared. Approximately 1,500 12-day-old bluefin tuna larvae (average total length: approximately 7.5 mm) were placed in each tank.

[0059] The larval feed of Example 1 was administered to the tanks in the coating area A using a spoon, approximately 10 times per day, approximately every hour starting in the morning, at a rate of approximately 3 g per administration. After the start of administration, 20 bluefin tuna larvae were sampled from each tank every other day, dissected under a stereomicroscope, and the presence or absence of larval feed in their stomachs was observed. The percentage of individuals with larval feed remaining in their stomachs was then calculated as the feeding rate (%). The results were 2.3% at 14 days of age, 7.5% at 18 days of age, and 23.0% at 20 days of age.

[0060] The aquaria in the coating area B and the control area were also evaluated in the same manner as the aquaria in the coating area A, using the larval feeds of Example 2 and Comparative Example 1, respectively. In the coating area B (Example 2), the values ​​were 0% at 14 days old, 8.3% at 16 days old, 20.0% at 18 days old, and 42.9% at 20 days old. In the control area (Comparative Example 1), the values ​​were 0% at 14 days old, 0% at 16 days old, 0% at 18 days old, and 19.7% at 20 days old.

[0061] The age at which feeding of the larval feed was first confirmed was 20 days in Comparative Example 1, 14 days in Example 1, and 16 days in Example 2. Furthermore, a feeding rate of around 10% was observed at 20 days in Comparative Example 1, 18 days in Example 1, and 16 days in Example 2. In Example 2, the feeding rate continued to increase steadily thereafter, exceeding 40% at 20 days of age, the highest feeding rate observed.

[0062] [Evaluation of changes in survival rate] When "Evaluation 1 of changes in feeding rate" was performed above, the changes in survival rate were also evaluated. Specifically, the number of dead fish collected when cleaning the bottom of each tank every morning was counted to determine the number of surviving fish, and the survival rate was calculated using the following formula. The survival rates for the coated groups A and B and the control group were as shown in Table 2. Survival rate (%) = (number of surviving fish each day) / (number of surviving fish at 12 days old - cumulative number of sampled fish) x 100 In the above formula, "cumulative number of sampled fish" is the cumulative number of larvae sampled in "Evaluation 1 of changes in feeding rate" above.

[0063]

[0064] During the feeding period with the compound feed from 13 to 16 days of age, the mortality rate was lower in Examples 1 and 2 than in Comparative Example 1, and a significant difference in survival rate was observed. From 17 days of age onwards, the survival rate tended to decrease due to factors such as cannibalism or collisions with the tank wall.

[0065] [Preparation of Larval Feed 2] (Example 3) A gelatin solution was sprayed twice in the same manner as in Example 1 onto a compound feed (crumble feed) of the same size as the tuna hearts used in Example 1, to prepare larval feed with a coating (gelatin film) containing gelatin. The weight of the prepared larval feed was approximately 2 to 3% greater than that of the compound feed before the gelatin was attached (compound feed before gelatin coating). This was used as the larval feed of Example 3.

[0066] (Comparative Example 2) A compound feed (control feed) was prepared in the same manner as in Example 3, except that spraying of the gelatin solution was not performed. This compound feed was used as the larval feed of Comparative Example 2. In other words, the larval feed of Comparative Example 2 did not have a coating portion containing gelatin.

[0067] (Comparative Example 3) A mixture containing the raw materials of the compound feed used in Example 3 and gelatin was used to prepare a compound feed containing gelatin having a size similar to that of the compound feed for tuna heart used in Example 1. The gelatin content in the compound feed was 2 to 3 wt %. This compound feed was used as the larval feed of Comparative Example 3. This larval feed did not have a coating containing gelatin.

[0068] [Feeding Ability Evaluation 2] This evaluation used yellowtail larvae hatched at the Oita Marine Research Center. The yellowtail larvae used were 52 days old and approximately 20 mm in total length. Using these yellowtail larvae, a gelatin-coated area, a control area, and a gelatin-mixed area were prepared. Approximately 1,000 yellowtail larvae were housed in a 1-ton tank in each area, and feeding ability was evaluated. Specifically, the gelatin-coated area was fed the larvae feed of Example 3, the control area was fed the larvae feed of Comparative Example 2, and the gelatin-mixed area was fed the larvae feed of Comparative Example 3. The swallowing ratio (= number of swallowed tails / number of spit-out tails) during feeding was measured. Larvae feed (approximately 1 g) was fed 10 times in each area, and the number of swallowed tails and spit-out tails were visually counted. The results are shown in Table 3.

[0069] As shown in Table 3, the swallowing ratio of the gelatin-coated group (Example 3) was approximately 2.8 times and approximately 2.4 times the swallowing ratios of the control group (Comparative Example 2) and the gelatin-mixed group (Comparative Example 3), respectively.

[0070]

[0071] Larvae Feed Preparation 3 (Example 4) Commercially available agar powder (Wako Pure Chemical Industries, Ltd.) was mixed with distilled water to an agar concentration of 10 wt % to prepare an agar solution in which the agar was dissolved in water. Larvae feed with a coating was prepared in the same manner as in Example 1, except that tuna hearts (manufactured by Nisshin Marubeni Feed Co., Ltd.) with the same size but different color and components as those in Example 1 were used as the compound feed, and agar solution was used instead of gelatin solution. The weight of this larvae feed with a coating made of agar was approximately 2.5 wt % heavier than the compound feed before being coated with the agar solution. This was designated the larvae feed of Example 4.

[0072] Example 5 Commercially available fish-derived gelatin (product name: Jellyace Gelatin Fine Mesh F, Yasu Chemical Industry Co., Ltd.) was mixed with distilled water to a gelatin concentration of 10% by weight, and the mixture was heated in a microwave oven until the granules were no longer visible, producing a gelatin solution in which the gelatin was dissolved in water. Larval feed having a coating was prepared in the same manner as in Example 4, except that this gelatin solution was used instead of the agar solution. The weight of this larval feed having a coating made of gelatin was approximately 10% greater by weight than the compound feed before being coated with the gelatin solution. This was designated the larval feed of Example 5.

[0073] [Evaluation of Changes in Feeding Rate 2] An agar area (one 1-ton black polycarbonate tank) and a gelatin area (one 1-ton black polycarbonate tank) were prepared. Approximately 1,500 12-day-old bluefin tuna larvae (average total length: approximately 7.5 mm) were placed in each tank.

[0074] The larval feed of Example 4 was administered to the agar tanks using a spoon, approximately 10 times per day, approximately every hour starting in the morning, at a rate of approximately 6 g per feeding. At a predetermined age, 20 or 40 bluefin tuna larvae were sampled from each tank and dissected under a stereomicroscope to observe the presence or absence of larval feed in their stomachs (16- and 22-day olds: 40 fish each, 26-day old: 20 fish each). The proportion of individuals with larval feed remaining in their stomachs was then calculated as the feeding rate (%).

[0075] As a result, the feed intake rate in the agar group (Example 4) was 9.5% at 16 days of age, 7.3% at 22 days of age, and 30.0% at 26 days of age. The feed intake rate in the gelatin group (Example 5) was 8.0% at 16 days of age and 14.1% at 22 days of age. Thus, when a coating containing agar was provided, the feed intake rate was increased similarly to when a coating containing gelatin was provided.

[0076] The present invention provides a method for raising fish larvae that can improve the survival rate of the larvae and promote their growth, as well as a method for producing the same.

[0077] 10...Main body portion, 20...Covering portion, 40...Food for larvae.

Claims

1. A feed for larval fish comprising a main body made of a compound containing fish-derived ingredients and a gel-like covering that covers the main body.

2. The feed for larvae according to claim 1, wherein the diameter of the main body when converted into a sphere of the same volume is 0.25 to 5 mm.

3. Larval feed according to claim 1 or 2, which contains a feeding promoter.

4. The feed for larvae according to claim 1 or 2, which has a sedimentation velocity in seawater of less than 3.5 cm / sec.

5. Larval feed according to claim 1 or 2, wherein the salinity of the water contained in the main body is lower than that of seawater.

6. The feed for larvae according to claim 1 or 2, wherein the larvae belong to the order Perciformes.

7. Larval feed according to claim 1 or 2, wherein the weight ratio of the covering portion to the main body portion is 1 to 20% by weight.

8. A method for raising fish, comprising: a first step of feeding live feed to larvae; and a second step of feeding the larvae feed according to claim 1 or 2 to the larvae, wherein the second step is started after the first step is started.

9. The method for raising fish according to claim 8, wherein the second step is started after the first step is completed.

10. A method for raising fish according to claim 8 or 9, in which the hatched larvae are not fed.

11. The method for raising fish according to claim 8 or 9, wherein the second step is initiated when the larvae are between 10 and 30 days old.

12. A method for producing feed for larval fish, comprising the steps of attaching a gel-like component to the surface of a main body made of a compound containing fish-derived components, and coating the surface of the main body with a gel-like coating.

13. A method for using feed for raising larval fish, the feed comprising a main body made of a compound containing fish-derived ingredients and a gel-like covering covering the main body.

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