JP6468998B2 - Spawning induction method for marine fish-eating fish - Google Patents

Description

  The present invention relates to a method for inducing spawning of marine fish-eating fish.

In recent years, artificial breeding of large fish has become important in an industry called an animal handling business, especially in fish farming, aquariums, and ornamental fish sales. At the same time, it may be necessary to produce high-value-added lines by breeding, etc., or in the case of fish species where young fish are collected for aquaculture. Reproduction in Japan is also an important issue. In order to reproduce fish under artificial breeding, it is necessary not only to give proper feed to promote growth but also to give appropriate environmental stimuli to promote sexual maturation and egg-laying behavior. Fish sexual maturation and egg-laying behavior are stimulated through the regulation of various endogenous factors including sex hormones under various environmental stimuli. The effects of these maturation factors and environmental stimuli on how sexual maturity and egg laying occur vary from fish species to fish species, and the mechanism needs to be investigated for each target species.
On the other hand, fish belonging to natural mackerel, which are marine fish-eating fish, spawn from spring to summer while migrating. At this time, it is not well understood what environmental stimuli cause the spawning. For example, in bluefin tuna, larvae have been confirmed in a wide temperature range from around 20 ° C to around 30 ° C in the natural sea area, but in observation under artificial breeding, at least simply a simple mechanism of spawning at a specific water temperature There is a suggestion that it is important that the number of days from 23 ° C to 24 ° C is short. In addition, it has not been confirmed whether or not the eggs obtained in this way were eggs that could grow to hatched larvae (Non-Patent Document 1).

  It has become clear from studies using many species of fish, including salmonids, that fish sexual maturation is controlled by the function of various hormones in the hypothalamus-pituitary-gonad system. ing. First, 10-amino acid peptide GnRH (gonadotropic hormone-releasing hormone) is produced in the hypothalamus. Subsequently, GnRH acts on the pituitary gland to stimulate the secretion of gonadotropic hormone (GTH). In addition, GTH acts on the gonads, and in females the growth of oocytes through the production of egg yolk through the production of estradiol 17β (E2), followed by 17α, 20β-dihydroxy-pregnen-3-one (DHP) Promotes maturity and ovulation. In males, testicular development and sperm differentiation are promoted through 11-ketotestosterone (11KT) production, and defecation is promoted through DHP. And it is thought that this series of cascades function properly and sexual maturity progresses, resulting in spawning behavior. Using this principle, a sustained release agent that secretes GnRH can be surgically implanted in the muscle or abdominal cavity, or injected in the form of an aqueous solution dissolved in physiological saline. It is also possible to promote final maturation and spontaneous egg-laying behavior even in individuals who do not have egg-laying behavior.

GnRH is a peptide hormone consisting of 10 amino acid residues. The existence of three types of molecules in many fish, namely GnRH1, GnRH2, and GnRH3, is known. The physiological function of each molecule has been reported in various fish species, and GnRH1 is thought to be responsible for the control of sexual maturation via GTH secretion. However, many things are still unknown. The amino acid sequence of GnRH1 may differ little by little depending on the fish species, and GnRH2 and GnRH3 are often conserved throughout the fish species, but this is not the case. For example, in Indian murrel, two types of GnRH molecules having a unique amino acid sequence have been found, and GTH secretion-inducing ability is said to be superior to existing GnRH molecules (Patent Document 1). Furthermore, the titer of the maturation-inducing ability of each GnRH molecule does not necessarily match the physiological role in vivo. Thus, the relationship between the polymorphism of the amino acid sequence and the strength of the physiological function and maturation inducing ability in the living body has not been clarified in detail. In order to promote the maturation of fish, agonists such as [des-Gly ¹⁰ , D-, which are based on mammalian GnRH1 and are chemically modified to increase the effect by several tens to several hundreds of times. Ala ⁶ ] -LH-RH ethylamide acetate (Sigma-Aldrich) and the like are generally used.

In many fish species, an aqueous solution in which GnRH is dissolved in physiological saline or the like, or cholesterol pellets or biodegradable polymers that release GnRH slowly, are administered intramuscularly or intraperitoneally. By embedding in the body, it is possible to promote maturation and induce egg laying. However, it is known that its efficacy varies depending on the target fish species. In many cases, it has been used for individuals whose gonadal development has already progressed to some extent before administration of exogenous GnRH. Yes, exogenous GnRH is thought to mainly induce final maturation and ovulation. For example, it has been reported that in herring, southern flounder, and summer flounder, no induction of maturation is observed even when GnRH is administered to individuals in the early to middle stages of egg yolk accumulation. However, in Ayu, the effect of exogenous GnRH to promote the accumulation of egg yolk from a relatively early stage has been reported, and in red sea bream, it has succeeded in inducing the maturation of immature individuals in the non-laying stage and laying eggs. . In rainbow trout, the ability to promote maturation has been reported by administering sex steroid hormones and GnRH to immature individuals, whereas in striped bass, sex steroid hormones and GnRH are administered to immature individuals. There was no gonad development. These facts show that the effect of promoting maturation by administration of exogenous GnRH varies depending on the fish species.
In addition, it has been reported that maturation and egg-laying can be promoted by mixing GnRH with dietary feed and orally. It is thought that GnRH peptide in the feed is partly taken from the digestive tract without being decomposed, thereby promoting GTH production and promoting maturation and spawning. Examples of marine fish so far include examples in which egg laying was induced by oral administration of GnRH in omnivorous guindara and spotted seatrout (Non-patent Documents 2 and 3). However, even though they are marine, they are not fishy. Furthermore, gindara and spotted seatrout are fish species that can lay eggs even under artificial breeding by controlling the breeding environment such as day length and water temperature. For this reason, artificial spawning induction of these fish species is not as difficult, and the spawning induction ability of GnRH confirmed in these fish species cannot be applied to all fish species. Moreover, even in these fish species, not all the individuals that were administered spawned, suggesting the uncertainty of maturation induction by GnRH administration. In particular, in tuna, which are marine fish-eating fish, the intake of food is reduced during the spawning season, so far no induction of spawning has been attempted by such a technique (Non-patent Document 4).

JP 2009-292836 A

Bulletin of Fisheries Research Center Separate volume 4 (2006) 157-171 Aquaculture 80 (1989) p363-370 Fish Physiology and Biochemistry 8 (1990) p497-499 Aquaculture 249 (2005) p303-309

  It is an object of the present invention to induce spawning under artificial breeding, particularly spawning eggs with good egg quality, in marine fish-eating fish, in particular, in the subspecies fish.

  Reproductive hormone is orally administered to marine fish-eating fish.

The gist of the present invention is the following (1) to (7).
(1) A method for inducing spawning of marine fish-eating fish characterized by oral administration of reproductive hormones.
(2) The spawning induction method according to (1), wherein the marine fish-eating fish is a mackerel subfamily.
(3) The egg-laying induction method according to (1) or (2), wherein the mackerel subfamily is a mackerel fish.
(4) The spawning induction method according to any one of (1) to (3), wherein the marine fish-eating fish is a fish species having an adult body length of 30 cm or more.
(5) The method for inducing spawning according to claims 1 to 4, wherein the oral administration is performed by mixing with feed.
(6) The egg-laying induction method according to claim 5, wherein the feed has a protein content of 5% by weight or more and less than 90% by weight.
(7) The egg-laying induction method according to any one of claims (1) to (6), wherein the reproductive hormone is GNRH.
(8) The egg-laying induction method according to (7), which is artificially produced by GNRH.
(9) The egg-laying induction method according to (7) or (8), wherein GNRH is administered in an amount of 0.01 to 100 mg / kgBW / day.
(10) The egg-laying induction method according to (1) to (9), wherein hatched larvae can be obtained after egg-laying induction.
(11) The egg-laying induction method according to (10), wherein the hatched larvae are obtained at a hatching rate of 5% or more.
(12) The egg-laying induction method according to (1) to (11), wherein the water temperature is adjusted in addition to oral administration of reproductive hormones.
(13) The egg-laying induction method according to any one of (1) to (12), wherein the egg-laying induction is performed while rearing in an onshore water tank.
(14) The spawning induction method according to any one of (1) to (13), wherein the marine fish-eating fish is a fish species that does not spawn only by adjusting sunshine and water temperature while being raised in a land tank.
(15) Eggs, hatched larvae and adult fish obtained by the egg-laying induction method according to (1) to (14).

  According to one embodiment of the present invention, it is possible to induce spawning of marine fish-eating fishes, in particular, mackerel subfamily fish, and fish species having high migratory activity of mackerel fish. Moreover, according to another aspect, the spawning induction | guidance | derivation of marine fish-eating fish which is 30 cm or more in length of an adult fish can be carried out. Moreover, according to another aspect, an egg with good egg quality can be induced and an egg with a high hatching rate can be induced. Furthermore, according to another aspect, egg-laying can be induced while being raised in an onshore water tank.

FIG. 1 shows the number of eggs laid by sesame mackerel administered with reproductive hormone, accumulated daily. FIG. 2 is a bar graph showing the number of eggs laid in the reproductive hormone-administered suma and the number of hatching from the eggs for each day, and the water temperature at that time is shown by a line graph. FIG. 3 is a bar graph showing the number of eggs laid, the number of fertilized eggs and the number of hatched eggs, which were orally administered while adjusting the reproductive hormone water temperature.

  The marine fish of the present invention refers to fish that inhabit the sea, and is represented by teleost fish, especially true fish. Authentic fish include Persian fishes, and Persian fishes include Macaques. The fish of the fish-eating fish of the present invention refers to fish mainly containing fish, and is represented by mackerel fish. Fish-eating fish need to break down the protein of many fish that serve as food, and are regulated by enzyme activity, food gastrointestinal residence time, enteric bacteria, and the like.

  As fish belonging to the subfamily Sabaidae, in addition to mackerel fish, fish belonging to the marlin department, the swordfish family, and the licorice family are known, and examples thereof include marlin, swordfish, and redfish. Examples of the fish belonging to the mackerel family include tuna such as chub mackerel, sesame mackerel, guru bear, suma, sawara, hagatsuo, bonito, soda bonito, and bluefin tuna, Atlantic bluefin tuna, southern bluefin tuna, yellowfin, binnaga, bigeye, cochinaga, etc. For use in the present invention, mackerel sub-fishes with high fish-eating properties are preferred, and mackerel fishes with high migratory properties are more preferred. Examples of mackerel fish with high migratory activity include chub mackerel, sesame mackerel, skipjack, bluefin tuna, Atlantic bluefin tuna, and southern bluefin tuna. It is known that a highly migratory fish species has a large mouth and needs to swallow a large amount of seawater at the same time as the fish that feeds it and take in a large amount of dissolved oxygen.

  Induction of egg-laying in the present invention refers to promoting egg-laying in fish. Egg laying is performed through ovulation and egg release stages. Ovulation is a phenomenon in which an oocyte is formed in the female ovary of an adult fish and detaches from the follicular tissue of the ovary. Ovulation is a phenomenon that is released to the outside of the body. Oviposition that occurs spontaneously with mating or fertilization for next-generation reproduction is egg laying. In fish, eggs accumulated in the ovaries may be released outside the body due to some stimulus, but such spawning is also seen when eggs are not fully prepared for egg laying, fertilized properly and hatched larvae It is distinguished from laying eggs that can be obtained.

  In the present invention, an adult fish means a fish that has grown reproductively, and the body length (tail difference length) is 25 cm or more for chub mackerel or sesame, 40 cm or more for suma, 42 cm or more for skipjack, In the case of bluefin tuna, it means an individual of 115 cm or more, and in the case of swordfish, it is 140 cm or more. In terms of body weight, it is about 300 g or more for chub mackerel, sesame mackerel, about 1,400 g or more for suma, about 1,500 g or more for skipjack, about 30 kg or more for bluefin tuna, about 70 kg for swordfish It becomes the above individual.

The reproductive hormone in the present invention refers to a hormone related to reproductive activity, and includes any one that has an effect of inducing spawning in fish. Specifically, in addition to GnRH, LH and FSH, E2 and DHP may be used in the female.
In addition to the hypothalamus extract, pituitary gland extract, and purified products thereof containing a high concentration of the reproductive hormone, those artificially synthesized by chemical methods can be used. Any method may be used for artificial synthesis by a chemical method, but in the case of peptide hormones, it is preferable to use a peptide synthesizer from the viewpoint of convenience.

GnRH is a peptide hormone consisting of 10 amino acids, and its sequence is known to be HWSYLRPNHE in rainbow trout. In the present invention, it is preferable to use a peptide having this sequence.
When using artificially synthesized LHRHa instead of GnRH, HWSYaLRPNHE, which is less susceptible to degradation by endopeptidase by binding D-type alanine between Y and L, acylates the end of E and degrades by exopeptidase There are various types such as HWSYLRPNHEt that is less susceptible to degradation, and HWSYaLRPNHEt that is modified with both of these. Any of these may be used, but HWSYaLRPNHEt that is less susceptible to degradation from peptidases is particularly preferred.

  Since the life cycle of fish is approximately 24 hours a day, the dose of reproductive hormone is basically 24 hours a day. In addition, the action of reproductive hormone is usually proportional to blood concentration, and the blood volume is proportional to fish weight. For this reason, the dose of reproductive hormone is based on 1 kg fish weight (BW). According to the present invention, the dosage of reproductive hormone is preferably 0.01 mg / kg BW / day or more in order to promote egg laying in fish, and 0.1 mg / kg BW / day or more is required in order to obtain eggs with good egg quality and hatching. In order to induce more strongly, 1 mg / kg BW / day or more is particularly preferable. The upper limit is not particularly limited as long as the fish does not cause side effects. However, the higher the concentration, the higher the cost.

  According to the present invention, when a reproductive hormone is administered, a predetermined dose may be administered once a day or may be divided into several times a day. Since the fish meal cycle is once a day after sunrise or before sunset, or twice a day after sunrise and before sunset, it is preferably performed once or twice a day. If administration is performed for one day, egg-laying can be induced, but it may be performed every day. It is preferable to continue every day because more eggs are induced.

  For oral administration, reproductive hormones may be administered directly or mixed with feed. When peptide hormones are mixed with feed, it is preferable to mix them with feed having a low peptidase activity. The activity of peptidase in feed can be reduced by heat treatment, acid treatment, alkali treatment, drying treatment, pressure treatment and the like.

When reproductive hormone is administered to fish, spawning is promoted, but hatched larvae may not be obtained. This is understood to be a problem with egg quality. Egg quality refers to the biochemical composition of an egg, and is evaluated by the probability that the phenomenon of levitation, fertilization, embryogenesis, and hatching observed after egg laying is observed. Even if eggs are forcibly laid by reproductive hormone administration, eggs that do not have egg quality are ovulated. As a result, hatched larvae cannot be obtained, which is not meaningful. According to the present invention, it is possible to obtain an egg with high egg quality, which is evaluated by the ascent rate, fertilization rate, embryo formation rate, hatching rate, and the like. The ascent rate is based on the total number of eggs collected, with the eggs that have emerged within 5 minutes from the start of measurement in the seawater or similar osmotic pressure in which the fish are bred after collection of the released eggs. Defined as the percentage of floating eggs. The fertilization rate is defined as the ratio of the number of fertilized eggs to the total number of observed eggs, where the eggs that have been released are fertilized by sperm and the eggs that have been confirmed to be broken are fertilized eggs. For fertilization, fish may be reared in a mixed sex, and fertilized in a rearing environment after egg release and fertilized as it is. In addition, sperm collected from a male in advance after egg collection may be fertilized by placing it in an artificial breeding. Embryo formation rate is defined as the ratio of embryonated eggs to the total number of eggs observed, where embryos formed after cleavage are defined as embryonated eggs. Embryo formation is carried out with the naked eye or under a microscope, and is defined as the ratio of the number of embryonated eggs to the total number of eggs observed, with the embryo formed as a result of cleavage and formation of the head and tail. Embryo formation usually takes place between 1 and 3 days after fertilization. The hatching rate is defined as the number of hatched larvae relative to the total number of eggs observed, where hatched larvae are hatched larvae. Hatching usually takes place between 1 and 7 days after fertilization.
Considering the later use, the ascent rate is preferably 10% or more, particularly preferably 20% or more. The fertilization rate is preferably 30% or more, particularly preferably 50% or more. The embryogenesis rate is preferably 10% or more, particularly preferably 20% or more. The hatching rate is preferably 5% or more, particularly preferably 10% or more, and further preferably 15% or more.

  When reproductive hormone is administered orally, it is preferable to adjust the growth temperature as appropriate. The growth temperature varies depending on the fish species, but egg-laying is not easily induced by stress near the upper or lower limit of the temperature range in which it can grow. For this reason, it is preferable to induce around the median temperature at which growth is possible. The water temperature can be adjusted at the same time as oral administration of reproductive hormone, or prior to oral administration of reproductive hormone, 18 ° C to 21 ° C for spring spawning mackerel species such as sesame mackerel and chub mackerel. It is preferable to induce at 24-27 ° C. for spawning mackerel species, and 18-22 ° C. for summer spawning swordfish and marlins such as swordfish. The water temperature is preferably adjusted 1 day to 200 days before the spawning induction, and more preferably 3 days to 90 days. The water temperature can be adjusted by using a heater, a cooler, or a combination thereof. In the adjustment, the temperature may be adjusted within a range of ± 2 ° C from the set temperature, preferably within a range of ± 1 ° C, and more preferably within a range of ± 0.5 ° C. Although the set temperature can be changed in the vicinity of the median temperature at which growth is possible, in order to reduce environmental irritation to fish, it is preferable to continue breeding at the same temperature during oral administration of reproductive hormones.

  When reproductive hormones are mixed with feed and administered orally, feed nutrients should be provided without excess or deficiency. Preferably, a feed having a protein content of 5% by weight or more, more preferably 10% by weight or more, and particularly preferably 15% by weight or more may be given. Particularly, in the case of raw bait, it is preferable to give a bait having a protein content of 5% by weight or more, more preferably 10% by weight or more, and particularly preferably 15% by weight or more as a raw material. In addition, in the mixed feed, it is preferable to feed the whole feed with a protein content of 5% by weight or more, more preferably 15% by weight or more, particularly preferably 25% by weight or more, and most preferably 35% by weight or more. If the diet contains too little protein, orally administered reproductive hormones are susceptible to degradation by peptidases contained in the gastrointestinal tract, affecting the induction rate of spawning. Also, it causes poor growth and no egg-laying behavior is observed. On the other hand, when the protein content in the food is too high, the protein in the food induces peptidase in the digestive tract, and the reproductive hormone administered orally is easily degraded, affecting the induction rate of spawning. Moreover, calorie deficiency is relatively short, and egg-laying behavior is not seen. In order to avoid this, it is preferable to give a feed having a protein content of 90% by weight or less, preferably 80% by weight or less, more preferably 70% by weight or less, and particularly preferably 60% by weight or less.

Fish growth may be adjusted by administering both feed with and without reproductive hormones. In this case, it is preferable that each nutrient component such as protein, lipid, vitamin, etc. is given without excess or deficiency in the total of both feeds.
The protein in the present invention constitutes the body of a fish or consists of amino acids contained in feed. Protein contained in feed is measured by the official method of feed analysis standards established by the Ministry of Agriculture, Forestry and Fisheries.

  According to the present invention, egg-laying can be induced even when reared in an onshore water tank. The onshore water tank can be any type such as breeding water circulation type or pouring type, but it is preferable that the water temperature can be adjusted. The size is preferably about 10 t for suma, 0.5 t for sesame and mackerel, 10 t for skipjack, and about 70 t for bluefin tuna.

  According to the present invention, spawning can be induced even for fish species for which it is very difficult to induce spawning while raising a land tank. By the present invention, examples of fish species that can induce spawning in captive land tanks include suma, sesame mackerel, bonito, skipjack, bluefin tuna, yellowfin and cocinaga.

  Examples of the present invention will be described below, but the present invention is not limited thereto.

<Test Example 1> Spawning induction of sesame mackerel The experiment was performed three times, and each test was performed for 10 days. The sesame mackerel used individuals caught in Tateyama Bay, Chiba Prefecture. Table 1 shows the relationship between the time of each experiment, the water temperature, and the weight of the test fish used in the test. A total of 8 males and 4 males were housed in a 1-ton FRP water tank. The test plot is a mixed feed supplemented with LHRHa (Hayashi and Sangyo, White Breeding No. 6: crude protein 57.0% or more, crude ash content 19.0% or less, crude fat 8.0% or more, crude fiber 4.0% or less), fish weight 1 There were 4 oral administration zones (OA zones) in which 0.048, 0.24, 1.2, and 6.0 mg of LHRHa per kg were fed in a day.
Further, as a positive control, an implant section (imp section) in which a sustained release pellet added with LHRHa, which is a general administration method of LHRHa, was implanted into the abdominal cavity was provided. A method for producing sustained-release pellets is shown below. First, 5.9 mg of reagent LHRHa was dissolved in 3 ml of 70% ethanol. Subsequently, 3 ml of LHRHa solution was added to 3,750 mg of cholesterol, mixed, and dried at room temperature for 30 minutes. Further, 750 mg of cocoa butter was added and mixed, and dried overnight at room temperature. Using an acrylic pelletizer, 45 mg cholesterol pellets containing 50 μg of LHRHa per tablet were prepared from the powder obtained by the above operation.
The amount of LHRHa added to the pellet was adjusted to a dose of 0.1 mg / kg fish weight. Furthermore, a non-administration group in which LHRHa was not administered was established as a negative control group.
The drained pipe adjusted to the height of the breeding water surface was provided on the wall surface of the aquarium, and the laid eggs were collected by receiving the drainage from there through an egg-collecting net. The recovered eggs were suspended in 1 L seawater, 2 ml of which was transferred to a 12-well plate, and the number of eggs was counted. The total number of eggs was obtained by multiplying the average value measured three times by 500. Egg collection and measurement were performed daily during the experiment. The cumulative total number of eggs measured in this way is shown in Table 2 as the cumulative total number of eggs. Further, FIG. 1 shows a graph of the transition of the cumulative total number of eggs every day for each test section. Next, among the eggs in 2 ml used for measuring the total number of eggs, the number of eggs that floated on the surface of the water within 5 minutes is the number of floating eggs, and the eggs that have been confirmed to be broken by microscopic observation among the floating eggs Was the fertilized egg number, and the number of larvae hatched until 2 days later was measured as the number of hatched larvae. This is shown in Table 3. Furthermore, the floating egg rate (= floating egg number / total egg number x 100), fertilized egg rate (= fertilized egg number / total egg number x 100), and hatching rate (= hatched larvae number / total egg number) were obtained. . This is shown in Table 4. In the implant group, although the total number of eggs obtained was large, the floating egg rate, fertilized egg rate, and hatching rate were not so high.

<Comparative Example 1-1>
The experiment was conducted for 10 days from June 30 to July 9, 2011. The sesame mackerel used individuals caught in Sagami Bay, Kanagawa Prefecture and Tateyama Bay, Chiba Prefecture. The average body weight of the test fish was 430 ± 17 g (n = 25). For each test area, 5 fish were sampled in a 1-ton FRP tank. As a test plot, feed mixed with LHRHa aqueous solution (Hayashi Kan Sangyo, White Breeding No. 6: composition is the same as in Example 1), 3.0, 12, and 30 mg of LHRHa per kg of fish weight per day There were three oral administration groups that were fed. In addition, as a positive control, an implant section in which a sustained release pellet added with LHRHa, which is a general administration method of LHRHa, was implanted into the abdominal cavity was provided. The amount of LHRHa added to the pellet was adjusted to a dose of 0.1 mg / kg fish weight. As a negative control group, a non-administration group in which LHRHa was not administered was established. The number of total eggs, the number of floating eggs, the number of fertilized eggs, the number of hatched larvae, and the values of the floating egg rate, fertilization rate, and hatching rate were measured in the same manner as in Experimental Example 1. As a result, egg laying was observed on the 8th day only in the 3.0 mg group administered orally, and 800 eggs were collected, but neither floated nor fertilized, and no hatched larvae were obtained. The water temperature during the test period was 21.0 to 23.8 ° C (average 22.8 ° C).

<Comparative Example 1-2>
The experiment was conducted for 10 days from April 4th to April 13th, 2012. The sesame mackerel used individuals caught in Tateyama Bay, Chiba Prefecture. The average body weight of the test fish was 497 ± 12 g (n = 30). For each test area, 5 fish (3 females, 2 males) were housed in a 1 ton FRP water tank. As a test plot, LHRHa aqueous solution infused mixed feed (Hayashi and Sangyo, White Breeding No. 6: composition is the same as in Example 1), 0.048, 0.24, 1.2, 6.0 mg of LHRHa per kg of fish weight per day There were three oral administration groups that were fed for consumption. In addition, as a positive control, an implant section in which a sustained release pellet added with LHRHa, which is a general administration method of LHRHa, was implanted into the abdominal cavity was provided. The amount of LHRHa added to the pellet was adjusted to a dose of 0.1 mg / kg fish weight. As a negative control group, a non-administration group in which LHRHa was not administered was established. The number of total eggs, the number of floating eggs, the number of fertilized eggs, the number of hatched larvae, and the values of the floating egg rate, fertilization rate, and hatching rate were measured in the same manner as in Experimental Example 1. As a result, egg laying was observed on the 7th day only in the implant section. The total number of eggs, the number of floating eggs, and the number of fertilized eggs were 2167, 333, and 41, respectively. The floating egg rate and fertilization rate were 15.4% and 1.9%, respectively. No hatched larvae were obtained. The water temperature during the test period was 13.5 to 17.3 ° C (average 15.3 ° C).

<Test Example 2> Induction of spawning of suma Thirteen tails (average weight 3057 ± 113 g) cultivated in Kushimoto-cho, Wakayama Prefecture were placed in a 70-t concrete aquarium, and spawning induction by LHRHa administration was attempted. The test was conducted from August to October 2011. First, a sustained-release pellet implant supplemented with LHRHa was implanted on August 9, followed by a live diet supplemented with LHRHa from August 28 to October 2. The sustained-release pellet was prepared so that the dose of LHRHa was 0.1 mg per 1 kg of fish body weight. LHRHa-added raw food is Lango Ha (74.2%, protein 17.2%, lipid, 5.5%, ash 3.0%, carbohydrate 0.1%) added to LHRHa mg to give a dose of 6.0 mg LHRHa per kg fish weight Was fed. The egg production was measured every day after the LHRHa implant until the end of oral administration, and the fertilization rate and the number of hatched larvae of the obtained eggs were also measured. This is shown in Table 5 as the total number. In addition, the total number of eggs and the number of hatched eggs on each measurement day are shown as a bar graph, and the water temperature at this time is shown as a line graph in FIG. The total egg number and hatching number are shown on the left axis of the graph, and the water temperature is shown on the right axis of the graph.

<Test Example 3>
From April to May 2012, 4 individuals in the same lot as the Suma of Test Example 2 were housed in a 10 tFRP water tank, and an attempt was made to induce egg laying by oral administration of LHRHa. The administration method and dose were the same as in Test Example 2, and the LHRHa-added live food was fed in three periods from April 17 to 22, May 2 to 6, and May 12 to 18. The water temperature was adjusted to be around 27 ° C. using a seawater heating / cooling unit (Marine River, Inc., MR-1800HVS-TR), and the average water temperature during the period was 27.2 ° C. (26.7-27.5 ° C.). It was. From April 17 to May 25, when oral administration was started, the total number of eggs laid, the number of fertilized eggs, and the number of hatched larvae were measured. This is shown in Table 6 as the total number. FIG. 3 is a graph showing the total number of eggs, the number of fertilized eggs, and the number of hatched eggs on each measurement day.

Claims (8)

A method for inducing spawning of mackerel subspecies,
If it is a mackerel fish species of spring laying eggs such as sesame and mackerel, 18 ℃ ~ 21 ℃,
If it is a mackerel fish species of summer eggs such as suma, bonito, tuna, 24-27 ° C,
In the case of swordfish and swordfish of summer laying eggs such as swordfish, induce at 18-22 ° C,
A method comprising orally administering GnRH.   The egg-laying induction method according to claim 1, wherein the mackerel subfamily is a mackerel fish.   The spawning induction method according to claim 1 or 2, wherein the mackerel subfamily is an adult fish having a body length of 30 cm or more.   The egg-laying induction method according to any one of claims 1 to 3, wherein the oral administration is performed by mixing with feed.   The egg-laying induction method according to claim 4, wherein the feed has a protein content of 5 wt% or more and less than 90 wt%.   The egg-laying induction method according to any one of claims 1 to 5, wherein GnRH is artificially produced.   The egg-laying induction method according to any one of claims 1 to 6, wherein the water temperature is adjusted in addition to oral administration of reproductive hormones. The egg-laying induction method according to any one of claims 1 to 7, wherein the egg-laying induction is performed while rearing in an onshore water tank.

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