Feed for aquaculture fish, breeding method, and intestinal epithelium protective agent

Abstract

To provide a feed for improving feeding volume and survival rate associated with seawater acclimation in marine aquaculture.SOLUTION: It has been discovered that incorporating lactic acid bacteria, particularly Lactococcus lactis subsp. lactis strain BF3, into a feed administered after seawater acclimation results in improvement of feeding volume and survival rate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a feed for cultured fish, a breeding method, and an intestinal epithelium protective agent. In particular, the present invention relates to a feed for cultured fish, a breeding method, and an intestinal epithelium protective agent that improve the feed amount and survival rate reduction during seawater acclimation in marine culture. [Background technology]

[0002] Seafood farming has become increasingly popular in recent years because there are few individual differences in size or taste, and because production can be done according to demand, making it possible to achieve a stable supply. In particular, in the case of complete aquaculture, where eggs are raised to produce parents, and then eggs are obtained from the parents, it is possible to select better individuals, making it possible to raise high-quality strains, which has led to branding. Furthermore, because aquaculture does not affect the ecosystem through overfishing or bycatch, demand for aquaculture is also increasing from the perspective of the SDGs.

[0003] Among farmed fish, salmonids are actively farmed in various regions. Salmonids spawn and grow in freshwater, and some species migrate to the sea, grow there, and then return to rivers to spawn. Rainbow trout farmed as trout salmon are born in freshwater, raised in freshwater until they reach a certain size, and then raised in seawater. Rainbow trout farmed in seawater are strains that are highly adaptable to seawater, but problems with marine aquaculture have been pointed out, such as a decrease in feed intake and a decrease in survival rate during acclimation to seawater.

[0004] In order to suppress the decrease in feed amount and survival rate during seawater acclimation and to perform efficient aquaculture, various efforts have been made (Patent Documents 1 and 2). Patent Document 1 discloses a seawater acclimation device for increasing the success rate of seawater acclimation of juvenile fish (smolts) that have demonstrated seawater adaptability. Patent Document 2 discloses fish feed containing sanguinarine or its derivatives as the main ingredient.

[0005] However, the seawater acclimation device described in Patent Document 1 is large-scale, so it cannot be easily installed and is costly. As disclosed in Patent Document 2, adding sanguinarine to feed to increase the success rate of seawater acclimation is a practical method in aquaculture. However, sanguinarine added to the feed in Patent Document 2 is a toxic polycyclic ammonium ion, so it is difficult to handle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2023-70394 A [Patent Document 2] JP 2016-163558 A [Patent Document 3] JP 2006-265181 A [Patent Document 4] Patent No. 5697788 [Patent Document 5] Patent No. 6152231 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to develop a feed that increases the success rate of seawater acclimation without using complex equipment or potentially toxic substances. Lactic acid bacteria are known to be effective in enhancing immune function in various animals. A feed that is effective in preventing disease by blending microorganisms such as lactic acid bacteria into feed for carp, a freshwater fish, has been disclosed (Patent Document 3), but the effect of lactic acid bacteria on the decrease in feed amount and survival rate immediately after acclimation to seawater has not yet been analyzed. The present invention aims to provide a feed that reduces stress on fish during acclimation to seawater and suppresses the decrease in feed amount and survival rate during acclimation to seawater by adding lactic acid bacteria. [Means for solving the problem]

[0008] The present invention relates to the following feed for farmed fish, a farming method, and an intestinal epithelium protective agent. (1) A feed for fish farming, characterized in that lactic acid bacteria are contained in a basic feed. By including lactic acid bacteria in the basic feed, it is possible to increase the daily feeding rate and reduce the mortality rate.

[0009] (2) The feed according to (1), which increases survival rate and feed intake. Analysis revealed that the intestinal epithelium was protected by the lactobacillus-supplemented feed. The increase in survival rate and feed intake was probably due to the intestinal epithelium being maintained in a near-normal state by the lactobacillus-containing feed.

[0010] (3) The feed according to (1), wherein the fish is a salmonid and the lactic acid bacterium is Lactococcus lactis subsp. lactis BF3 strain. Lactococcus lactis subsp. lactis BF3, a lactic acid bacterium isolated from chum salmon, is thought to be effective against salmonids.

[0011] (4) The feed according to (3), which is a feed for marine aquaculture. It has been shown that this feed is particularly effective for marine aquaculture of salmonids, as it increases the daily feeding rate and reduces mortality.

[0012] (5) The feed according to (4), which is given after acclimation to seawater. Since lactic acid bacteria are known to improve the balance of the intestinal flora, feed containing lactic acid bacteria may be given daily as a basic feed for aquaculture, but better effects can be obtained by giving it to the fish after acclimation to seawater.

[0013] (6) The feed according to any one of (1) to (5), wherein the lactic acid bacteria is contained in the feed at a ratio of 0.5% to 5% by weight. As shown in the examples, sufficient effects were observed even when 1% of the basic feed was added. Therefore, feed containing 0.5% or more of lactic acid bacteria can be expected to protect the intestinal epithelium. In addition, since it is lactic acid bacteria, there is no need to specify an upper limit, but since the intake of basic feed, which is related to the rate of weight gain, is thought to decrease relatively, it is desirable to set the upper limit of the amount of lactic acid bacteria added at 5%.

[0014] (7) A method for raising salmonid fish in marine aquaculture, comprising raising the fish using the feed according to (6) after acclimation to seawater in order to improve the feeding amount and survival rate during acclimation to seawater. As mentioned above, the decline in feeding amount and survival rate after seawater acclimation is a problem in marine aquaculture. This problem can be solved by feeding the fish with feed containing lactic acid bacteria, especially the BF3 strain.

[0015] (8) An intestinal epithelium protective agent for salmonid fish containing Lactococcus lactis subsp. lactis BF3 strain as an active ingredient. The analysis revealed that feeding the fish with the BF3 strain protected the intestinal epithelium and maintained a nearly normal state. Therefore, the composition containing the BF3 strain as an active ingredient functions as an agent for protecting the intestinal epithelium of salmonid fish.

[0016] (9) The intestinal epithelium protective agent according to (8), which is administered after acclimation to seawater. It has been revealed that after acclimation to seawater, the intestinal epithelium is destroyed when fed a normal diet. The intestinal epithelium protective agent of the present invention can protect this. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 shows the daily feeding rate for each experimental group. FIG. 2 shows the daily feeding rate for each experimental group at the end of the experiment. [Diagram 2] Graph showing the mortality rate in each experimental group. [Diagram 3]The figures show images of the digestive tract tissue of rainbow trout reared in each experimental group after three weeks of rearing. For comparison, images of the digestive tract tissue of rainbow trout that had been continuously reared in freshwater are shown. The bars in each microscopic image indicate 50 μm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Lactic acid bacteria is a general term for microorganisms that produce lactic acid from sugar through fermentation, and have traditionally been used in the production of fermented foods such as yogurt, cheese, pickles, and sake. It is said that lactic acid bacteria suppress the proliferation of so-called bad bacteria in the intestines and play a role in balancing the intestinal flora. However, the name lactic acid bacteria does not refer to a specific taxonomic species of bacteria, but rather to their properties, and the properties vary greatly depending on the species.

[0019] Lactic acid bacteria live not only in fermented foods but also in various places. By isolating lactic acid bacteria from a conventionally unused source, it is expected that lactic acid bacteria with new properties will be isolated. The present inventor has already isolated the lactic acid bacteria Lactococcus lactis subsp. lactis BF3 strain from the intestinal contents of male chum salmon (standard Japanese name: salmon) from Rausu, Hokkaido (Patent Document 4). The Lactococcus lactis subsp. lactis BF3 strain was deposited by the present applicant at the National Institute of Technology and Evaluation Patent Microorganisms Depositary Center under the accession number NITE P-01919 on August 21, 2014.

[0020] The BF3 strain isolated from the intestinal contents of chum salmon is different from strains isolated from dairy products, and has bile resistance, acid resistance, and salt resistance compared to the type strain Lactococcus lactis subsp. lactis NBRC100933. It has also been discovered and disclosed that it can ferment and solidify soy milk (Patent Document 5).

[0021] The present inventors have found that lactic acid bacteria, particularly Lactococcus lactis subsp. lactis BF3 strain, improve the decrease in feed intake and survival rate associated with seawater acclimation, and have completed the present invention. Here, rainbow trout is used for the analysis, but the feed shown below can be applied to fish that are aquacultured in seawater by acclimation. In particular, for salmonid fish, the lactic acid bacteria used below are isolated from chum salmon, so they can be used preferably. In addition, the lactic acid bacteria used are killed, but live bacteria may be mixed with the feed. From the viewpoint of the preservation of the feed, killed bacteria can be preferably used.

[0022] In addition, although the Lactococcus lactis subsp. lactis BF3 strain is used here, the present invention is not limited to this strain, and lactic acid bacteria isolated from the intestines of marine fish such as salmon can also be used. Alternatively, several lactic acid bacteria can be used in combination. However, since the product is administered to salmonid fish, it is preferable to use lactic acid bacteria isolated from salmonid fish, and it is particularly preferable to use the Lactococcus lactis subsp. lactis BF3 strain, the effectiveness of which has been demonstrated in the following examples.

[0023] In the following experiments, a basic feed containing 1% lactobacillus was used, but sufficient effects were observed in daily feeding rate and survival rate, so a smaller amount, 0.5% or more, of lactobacillus can be expected to be sufficient. Furthermore, when lactobacillus is used, especially killed bacteria, there is no need to set an upper limit, since there is no need to worry about side effects such as extreme imbalance of the intestinal flora. However, since there is a possibility that the amount of nutrients required for weight gain will be relatively reduced, it is preferable to use a content of 5% or less when rearing in seawater.

[0024] In addition, although the lactic acid bacteria are attached to the feed here, it goes without saying that the lactic acid bacteria may be mixed with other materials during the production of the feed. The feed used as the basic feed may be the feed normally used in aquaculture, and when the feed is produced by mixing the lactic acid bacteria, the feed may be produced by adding the lactic acid bacteria to the same composition as the basic feed.

[0025] The present invention will be described below with reference to practical data. [Experimental animals] Two-year-old rainbow trout (Oncorhynchus mykiss) were used in the experiment. They were randomly divided into a lactobacillus group fed the lactobacillus feed shown below and a control group fed a control feed.

[0026] [Experimental diet] Flounder EP-F6 (Nisshin Marubeni Feed) was used as the basic feed. Sterilized powder of lactic acid bacteria Lactococcus lactis subsp. lactis BF3 strain (hereinafter referred to as BF3 strain) was added to the basic feed at a ratio of 1% to prepare the lactic acid bacteria feed. For addition, a 2% gelatin solution was used at a ratio of 5% to the basic feed. Similarly, a 2% gelatin solution at a ratio of 5% to the basic feed was mixed with the basic feed without adding the BF3 strain, and used as the control feed. There was one experimental group and one tank, and the experimental group given a 0% feed that did not contain lactic acid bacteria was the control group, and the experimental group given a 1% BF3 strain feed was the lactic acid bacteria group.

[0027] [Seawater acclimation and rearing] Ten 2-year-old rainbow trout were placed in each 500L circular tank filled with fresh water. Seawater was poured in 24 hours after placement, and the fish were allowed to acclimate to seawater for 7 days. During the seawater acclimation period, the fish were not fed and were kept in still water. After the seawater acclimation period, the tank was switched to a flowing system, and the fish were continued to be kept in seawater.

[0028] After acclimation to seawater, the fish were fed satiation five days a week for three weeks. Body size (standard body length and body weight) was measured every seven days, and two fish from each experimental group were subjected to intestinal tissue observation. At the end of the experiment, five fish from each experimental group were taken, their body size was measured, and they were dissected and subjected to intestinal tissue observation. For tissue specimens, the intestines were fixed in Bouin's solution, and tissue sections made from the fixed intestines were stained with HE. Daily feeding rate and growth rate were calculated from the amount of food fed and body size.

[0029] [result] 1. Daily feeding rate after seawater acclimation The daily feeding rate at the end of the experiment is shown in Figure 1. Although no significant differences were observed, the daily feeding rate tended to be higher in the lactic acid bacteria group than in the control group. The daily feeding rate at the end of the experiment was 0.03% in the control group and 0.37% in the lactic acid bacteria group. Rainbow trout have poor feeding habits after acclimation to seawater, but it was shown that feeding was improved by feeding with marine lactic acid bacteria-added feed. Because feeding was improved by adding lactic acid bacteria, favorable effects on growth, such as weight gain, can be expected not only after acclimation to seawater, but also when used as regular feed for aquaculture.

[0030] 2. Mortality Rate The decline in survival rate after acclimation to seawater is also cited as a major problem in marine aquaculture. The effect of feed supplemented with lactic acid bacteria on mortality was analyzed (Figure 2). At the end of the experiment, the mortality rate was 50% in the control group, while it was 30% in the lactic acid bacteria group. It was clear that the mortality rate was lower in the lactic acid bacteria group than in the control group.

[0031] 3. Results of intestinal tissue observation The individuals from the control and lactobacillus groups were dissected and images of the intestinal tissue were observed by HE staining. For comparison, rainbow trout that had been continuously reared in freshwater were also dissected and images of the intestinal tissue were observed in the same manner. Figure 3 shows HE stained images of the intestinal epithelium from the control and lactobacillus groups after three weeks of rearing.

[0032] The epithelial tissue of the control group was broken down, and the animals were unable to absorb the digested nutrients (Fig. 3, control group). On the other hand, the intestinal epithelial tissue of the rainbow trout in the lactic acid bacteria group fed on feed containing the BF3 strain of lactic acid bacteria (Fig. 3, lactic acid bacteria group) showed more tissue breakdown than the individuals reared in freshwater (Fig. 3, freshwater rearing), but the degree of breakdown was less than in the control group. It is thought that adding lactic acid bacteria to the feed probably changed the intestinal flora to a more favorable state and accelerated the repair of the intestinal epithelial tissue. It is thought that the daily feeding rate increased and showed higher values ​​than in the control group due to the assistance of digestive function by the enzymes contained in the BF3 strain of lactic acid bacteria.

[0033] As described above, it has been clarified that the daily feeding rate and survival rate are increased by feeding the lactic acid bacteria-added feed in the feed and rearing method of the present invention. It has also been confirmed that the feed containing the lactic acid bacteria BF3 strain inhibits the destruction of the intestinal epithelium and is also effective as an intestinal epithelium protective agent. Therefore, it is considered that the feed protects the intestinal epithelium and contributes to the increase in the daily feeding rate and the increase in the survival rate.

Claims

1. A feed for fish farming, comprising: A feed characterized by containing lactic acid bacteria in a basic feed.

2. The feed according to claim 1, which increases survival rate and feed intake.

3. the fish is a salmonid, 2. The feed according to claim 1, wherein the lactic acid bacterium is Lactococcus lactis subsp. lactis BF3 strain.

4. The feed according to claim 3, which is a feed for marine aquaculture.

5. 5. The feed according to claim 4, which is given after acclimation to seawater.

6. The lactic acid bacteria is The feed according to any one of claims 1 to 5, characterized in that the feed contains the ingredient in an amount of 0.5% or more and 5% or less by weight.

7. A method for raising salmonid fish by using the feed according to claim 6 after acclimation to seawater in order to improve the amount of food to be fed and the survival rate during acclimation to seawater in marine culture of salmonid fish.

8. An intestinal epithelium protective agent for salmonid fish, containing Lactococcus lactis subsp. lactis BF3 strain as an active ingredient.

9. The intestinal epithelium protective agent according to claim 8, which is administered after acclimation to seawater.

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