Microorganism and application thereof in improving crab quality

Abstract

The invention discloses a microorganism and an application thereof in improving crab quality, the issatchenkia orientalis ZT-C2, lactobacillus acidophilus MD-7 and a combination thereof can significantly improve the weight gain of crabs, the content of edible part, the content of edible part protein, the content of edible part amino acid and the content of edible part fatty acid; the content of ammonia nitrogen and nitrite in the water body can be obviously reduced, and the water quality is improved.

Description

Technical Field

[0001] The invention belongs to the field of agricultural microorganisms, and in particular relates to microorganisms and applications thereof in improving crab quality. Background Art

[0002] Crabs belong to crustaceans and are an important aquatic economic crab. They are loved by the public because they are rich in protein and trace elements. Crabs contain more vitamin A, which helps the keratinization of the skin. Crabs also have anti-tuberculosis effects, and eating crabs is very beneficial for the recovery of tuberculosis, so the crab market is now in short supply. However, in the process of crab farming, bacterial diseases cause a sharp decline in production. In order to improve the quality and disease resistance of crabs, antibiotics or hormones are usually added to improve the resistance of crabs and shorten the growth cycle. However, the crab roe and crab paste content of crabs farmed in this way will be greatly reduced, and it is also harmful to human health.

[0003] In the current crab market where supply exceeds demand, farmers are trying to gain greater economic benefits, resulting in uneven crab quality. A green way is needed to improve the quality of crabs. Summary of the invention:

[0004] The purpose of the present invention is to provide a yeast and lactic acid bacteria and a combination of the two for the crab breeding environment, which not only improves the living environment of crabs but also improves the quality of crabs.

[0005] The first aspect of the present invention provides an oriental yeast strain ZT-C2, which was deposited in the General Microbiological Center of the China Microbiological Culture Collection Administration on June 25, 2018, with a strain deposit number of CGMCCNO.16008, and is classified and named as: Oriental yeast (Issatchenkia orientalis), and the address is: No. 3, No. 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, Postal Code: 100101. Patent 201910008806.8 has been disclosed.

[0006] The oriental yeast ZT-C2 strain of the present invention presents a typical Pichia kluyveri colony morphology, with large, thick, moist colonies, a smooth surface, opaque, viscous, monotonous colony color, and milky white yeast. It grows on the surface of a solid culture medium and is easy to pick up with a needle. The colony has a uniform texture, and the colors of the front and back sides and the center and the edge are consistent. The colony is relatively flat, and the surface and the edge are rough.

[0007] The second aspect of the present invention provides a Lactobacillus acidophilus MD-7, which has been deposited in the General Microbiology Center of the China Microbiological Culture Collection Administration on March 6, 2023, and is classified and named: Lactobacillus acidophilus (Lactobacillus acidophilus), with a deposit number of CGMCC NO.26750, and an address of: No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, Postal Code: 100101.

[0008] The Lactobacillus acidophilus MD-7 strain of the present invention presents a typical Lactobacillus acidophilus colony morphology, which is relatively small and presents a net shape, with a convex and rough colony surface and curled edges.

[0009] The present invention also provides a bacterial agent formed by the oriental yeast ZT-C2 or the Lactobacillus acidophilus MD-7, which can be cultured and prepared according to conventional methods in the art. Usually, the bacterial amount of the bacterial agent is 10 7 ~10 9 CFU / mL.

[0010] A third aspect of the present invention provides a composite bacterial agent comprising Issatchengensis ZT-C2 and Lactobacillus acidophilus MD-7.

[0011] The oriental yeast ZT-C2 provided by the present invention can grow to the maximum concentration on the PDA medium after 12 hours, can grow normally under the conditions of 20 to 45 degrees Celsius and pH 4 to 8, has high bacterial vigor and strong adaptability. The Lactobacillus acidophilus MD-7 can grow to the maximum concentration on the MRS medium after 24 hours, can grow normally under the conditions of 20 to 45 degrees Celsius and pH 4 to 8, has high bacterial vigor and strong adaptability.

[0012] In some embodiments, the mass ratio of Issaffron orientalis ZT-C2 to Lactobacillus acidophilus MD-7 is 1: (0.8-1.2), preferably 1: 1. The inventors found that this combination has strong adaptability. In some embodiments, the total bacterial count of the bacterial agent is 10 7 ~10 9 CFU / mL.

[0013] The fourth aspect of the present invention also provides the use of the oriental yeast strain ZT-C2, Lactobacillus acidophilus MD-7 or a single bacterial agent or a composite bacterial agent formed by them in promoting the growth of crabs; preferably, the use is to increase the weight and growth rate of crabs. In some embodiments, the specific method of the application is to directly sprinkle the oriental yeast strain ZT-C2, Lactobacillus acidophilus MD-7 or a single bacterial agent or a composite bacterial agent formed by them in the crab pond or add it to the feed eaten by the crabs, and the amount of the sprinkled can be adaptively selected according to the breeding area and the amount of crabs.

[0014] The fifth aspect of the present invention also provides the use of the oriental yeast strain ZT-C2, Lactobacillus acidophilus MD-7 or a single bacterial agent or a composite bacterial agent formed by them in improving the quality of crabs, preferably in increasing the content of edible protein, edible amino acids and edible fatty acids in the crabs. In some embodiments, the specific method of the application is to directly sprinkle the oriental yeast strain ZT-C2, Lactobacillus acidophilus MD-7 or a single bacterial agent or a composite bacterial agent formed by them in the crab pond or add it to the feed eaten by the crabs, and the amount of the sprinkled can be adaptively selected according to the breeding area and the amount of crabs.

[0015] The sixth aspect of the present invention also provides the use of the composite bacterial agent of the present invention in improving crab aquaculture water, preferably, in reducing the content of ammonia nitrogen and nitrite in aquaculture water. In some embodiments, the specific method of the application is to directly sprinkle the composite bacterial agent into the crab pond or add it to the feed eaten by the crabs.

[0016] The seventh aspect of the present invention also provides a method for increasing the growth rate of crabs, which is to directly sprinkle the oriental yeast strain ZT-C2, Lactobacillus acidophilus MD-7 or a single bacterial agent or a composite bacterial agent formed by them into the crab pond or add them to the feed eaten by the crabs.

[0017] The eighth aspect of the present invention also provides a method for increasing the growth rate or improving the quality of crabs, which is to directly sprinkle the oriental Issatchengen strain ZT-C2, Lactobacillus acidophilus MD-7, or a single bacterial agent or a composite bacterial agent formed by them into a crab pond or add them to the feed eaten by crabs.

[0018] The amount of the present invention can be spread according to the conventional method in the art, for example, a total inoculum amount of 10-13 kg per mu is added to the crab breeding water.

[0019] Beneficial effects of the present invention:

[0020] (1) The Issatchengensis ZT-C2 and Lactobacillus acidophilus MD-7 and their combination described in the present invention can grow to the maximum concentration on PDA medium and MRS medium respectively after 24 hours, and can grow normally under the conditions of 25-45 degrees Celsius, pH 5-9 and 25-45 degrees Celsius, pH 4-8, respectively, indicating that the combined bacteria have high vitality and strong adaptability, and can maintain their activity in natural water bodies.

[0021] (2) The oriental yeast ZT-C2 and Lactobacillus acidophilus MD-7 and their combination described in the present invention have been tested and shown that the bacterial combination can significantly improve the weight gain, edible part, edible part protein, edible part amino acid and edible part fatty acid content of crabs within a 48-day crab growth cycle under the conditions of a laboratory water tank.

[0022] (3) The oriental yeast ZT-C2 and Lactobacillus acidophilus MD-7 and their combination described in the present invention have been tested and found that the bacterial combination can significantly increase the weight of crabs under the conditions of an actual crab breeding base within a 120-day crab growth cycle, and significantly increase the edible part, edible part protein, and edible part amino acids of the crabs. This further indicates that the bacterial combination has a good effect on improving the quality of crabs.

[0023] (4) The combination of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 described in the present invention can also significantly reduce the content of ammonia nitrogen and nitrite in water bodies, thereby improving water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The colony morphology of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 for improving crab quality provided by the present invention;

[0025] Figure 2 The optimal culture temperature of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7;

[0026] Figure 3 The optimal culture temperature of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7;

[0027] Figure 4 Improvement of aquaculture water by Issaffron orientalis ZT-C2 and Lactobacillus acidophilus MD-7 in water tanks;

[0028] Figure 5 The effect of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 on the growth rate of crabs in water tanks;

[0029] Figure 6 Improvement of aquaculture water by Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 in water tanks;

[0030] Figure 7 Improvement of aquaculture water quality by Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 in actual crab aquaculture ponds;

[0033] Figure 8The effects of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 on the weight gain of edible crab parts, protein content, amino acid content and fatty acid content in actual crab farming ponds;

[0034] Fig. 9 Effects of Issatchenia orientalis ZT-C2 and Lactobacillus acidophilus MD-7 on ammonia nitrogen and nitrite contents in crab culture ponds. DETAILED DESCRIPTION

[0035] The present invention is described below with reference to the following examples, but the present invention is not limited to the following examples. The experimental methods in the following examples are conventional methods unless otherwise specified. The test materials used in the following examples are purchased from conventional biochemical reagent stores, such as sterile water, Tianzi Tianping, etc., which can be purchased through public channels.

[0036] The equipment and instruments used in the processes of the following examples are common equipment in the art, and other reagents and equipment well known in the art can be applied to the implementation of the following embodiments of the present invention.

[0037] The following examples further illustrate the content of the present invention, but should not be construed as limiting the present invention. Without departing from the spirit and substance of the present invention, modifications or substitutions made to the methods, steps or conditions of the present invention all fall within the scope of the present invention.

[0038] This study used single strains and strain combinations to evaluate crab weight gain rate, edible part weight gain, edible part protein weight gain, edible part amino acid content and edible part fatty acid content as evaluation criteria for crab quality. Ammonia nitrogen content and nitrite content in aquaculture water were used as evaluation criteria for aquaculture water.

[0039] If not otherwise specified, the culture medium used in the present invention is formulated as follows:

[0040] PDA medium: Potato dextrose agar medium (PDA): 20.0 g glucose, 200.0 g potatoes (cook and filter, keep the filtrate), 15.0 g agar powder, add distilled water to 1000 mL, natural pH, sterilize at 115°C for 30 min.

[0041] MRS medium: peptone 10g, yeast extract 5g, beef extract 10g, glucose 20g, sodium acetate 5g, diammonium citrate 2g, Tween 80mL, magnesium sulfate heptahydrate (MgSO4·7H2O) 0.58g, manganese sulfate tetrahydrate (MnSO4·4H2O) 0.05g, potassium dihydrogen phosphate (K2HPO4) 2g, agar powder 12g, deionized water 1000mL, 121℃, 1×105Pa sterilization for 20min. pH 6.12-6.2.

[0042] Example 1 Screening and Identification of Issatchenia orientalis and Lactobacillus acidophilus

[0043] 1. Initial screening of yeast

[0044] ① Collect 200 ml of aquaculture water from different places and depths and pour it into a 500 ml conical flask.

[0045] ② Oscillate on a constant temperature oscillator at 30℃ and 180r / min for 40 minutes to enrich the dominant bacteria.

[0046] ③ Take 3 ml of each sample and dilute it with a vortex oscillator and sterile water, i.e. dilute it to 10 -4 After the gradient, take 10 -4， , 10 -3 , 10 -2 , 10 -1 , and 100 μl of each of the original solutions were spread on PDA culture medium containing 1% potassium dichromate (because the breeding water contains a certain amount of mold, potassium dichromate can inhibit the growth of mold), and then inverted in a 28°C incubator to wait for single colonies to grow.

[0047] ④ The single colonies of different types were purified at least 3 times to obtain purified strains, and a strain of Issatchenkia orientalis ZT-C2 was obtained, which was deposited in the General Microbiological Center of China Microbiological Culture Collection on June 25, 2018, with the strain deposit number of CGMCC NO.16008, and the classification name is: Issatchenkia orientalis, the address is: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, Postal Code: 100101. Colony morphology is as follows Figure 1 Shown in the middle left picture.

[0048] 2. Preliminary screening of lactic acid bacteria

[0049] The same method as the initial screening of yeast is the enrichment method.

[0050] ① Collect 200 ml of aquaculture water from different places and depths and pour it into a 500 ml conical flask.

[0051] ② Oscillate on a constant temperature oscillator at 30℃ and 180r / min for 40 minutes to enrich the dominant bacteria.

[0052] ③ Take 3 ml of each sample and dilute it with a vortex oscillator and sterile water, i.e. dilute it to 10 -4 After the gradient, take 10 -4， , 10 -3 , 10 -2 , 10 -1, and 100 μl of each of the original solution were spread on MRS medium, which was then inverted in a 37°C incubator to wait for single colonies to grow.

[0053] ④ Purify the grown single colonies of different types at least 3 times to obtain purified strains, and obtain a strain of Lactobacillus acidophilus MD-7, which has been deposited in the General Microbiology Center of the China Microbiological Culture Collection Administration on March 6, 2023, and is classified and named: Lactobacillus acidophilus (Lactobacillus acidophilus), with a deposit number of CGMCC NO.26750, and the address is: No. 3, No. 1 Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences, Postal Code: 100101. Colony morphology is as follows Figure 1 As shown in the middle right picture.

[0054] Example 2 Determination of Suitable pH and Suitable Temperature of I. orientalis ZT-C2

[0055] ① Pick a single colony of Issatchenia orientalis ZT-C2 obtained in Example 1 and place it in a PDA liquid culture medium, and culture it with shaking at 28° C. for 12 hours to obtain a fresh seed solution.

[0056] ② Use a pH meter to adjust the pH of the PDA liquid culture medium to 4, 5, 6, 7, 8, 9, and 10. Take 5 ml of the bacterial solution and inoculate it into 50 ml of PDA liquid culture medium at pH 4-10, and repeat it 3 times for each group. Take 5 ml of the bacterial solution and inoculate it into 50 ml of PDA culture medium at normal pH as a control, and repeat it 3 times. Add 5 ml of sterile water to the blank group as a control, and repeat it 3 times. After 8 hours, measure its OD 600 The absorbance value at Figure 3 As shown in Figure 2, the strain can grow well at a pH value between 5 and 9.

[0057] ③ Pick a single colony of the oriental yeast ZT-C2 obtained in Example 1 and place it in a PDA liquid culture medium, and culture it at 28° C. for 12 hours to obtain a fresh seed solution.

[0058] ④ Take 15 test tubes with 5 ml of liquid PDA culture medium, and repeat in groups of three, for a total of 5 groups. Place them in a shaker at 20℃, 25℃, 30℃, 35℃, and 45℃, respectively, and shake and culture at 180r / min. After 12 hours, measure the OD 600 The blank group was used as the blank control. Figure 2 As shown in Figure 2, the strain can grow well at temperatures between 25°C and 45°C.

[0059] The above results show that the oriental yeast ZT-C2 described in the present invention can be applied to various acidic and alkaline water quality environments and has strong adaptability to temperature, and the strain has a wide range of application.

[0060] Example 3 Determination of the Optimal pH and Optimal Temperature of Lactobacillus acidophilus MD-7

[0061] ① Pick a single colony of Lactobacillus acidophilus MD-7 obtained in Example 1 and place it in MRS liquid culture medium, and culture it at 28° C. with shaking for 24 hours to obtain fresh seed liquid.

[0062] ② Use a pH meter to adjust the pH of the MRS liquid culture medium to 4, 5, 6, 7, 8, 9, and 10. Take 5 ml of the bacterial solution and inoculate it into 50 ml of MRS liquid culture medium at pH 4-10, and repeat it 3 times for each group. Take 5 ml of the bacterial solution and inoculate it into 50 ml of MRS culture medium at normal pH as a control, and repeat it 3 times. Add 55 ml of sterile water to the blank group as a control, and repeat it 3 times. After 12 hours, measure its OD 600 The absorbance value at Figure 3 As shown in Figure 2, the strain can grow well at a pH range of 4-8.

[0063] ③ Pick a single colony of Lactobacillus acidophilus MD-7 obtained in Example 1 and place it in MRS liquid culture medium, and culture it at 28° C. for 24 hours to obtain fresh seed liquid.

[0064] ④ Take 15 test tubes with 5 ml of liquid MRS medium, and repeat in groups of three, for a total of 5 groups. Place them in a shaker at 20℃, 25℃, 30℃, 35℃, and 45℃, respectively, and shake and culture at 180r / min. After 12 hours, measure the OD 600 The blank group was used as the blank control. Figure 2 As shown in Figure 2, the strain can grow well at temperatures between 25°C and 45°C.

[0065] The above results show that the Lactobacillus acidophilus MD-7 described in the present invention can be applied to various acidic and alkaline water quality environments and has strong adaptability to temperature, and the strain has a wide range of application.

[0066] Example 4 Test microbial strains and preparation methods thereof

[0067] Oriental yeast ZT-C2 and Lactobacillus acidophilus MD-7 were inoculated into PDA medium and MRS medium respectively, and cultured at 160 rpm and 28 °C for 24 h. The bacterial solution was collected and centrifuged at 6000 rpm for 10 min. The supernatant was removed and resuspended with sterile water. The above steps were repeated 5 times. The final bacterial solution concentration was adjusted to 1.0 × 10 8 CFU / mL, for later use. Oriental yeast ZT-C2 and Lactobacillus acidophilus MD-7 were combined in a weight ratio of 1:1 to form a composite bacterial agent for subsequent experiments.

[0068] Example 5 Effect of the composite bacterial agent on the physiological indicators of crabs under laboratory aquarium conditions

[0069] The yeast and lactic acid bacteria obtained in Example 4 were used as single strains and in combination to measure their actual effects on crab quality and water quality for crab farming.

[0070] ① Clean the aquarium: Because the actual simulation used in the experiment is carried out in an aquarium, first use tap water to carefully clean the aquarium, clean up the scale and garbage from the previous breeding, and dry it for 12 hours after cleaning. Add pond breeding water to the aquarium, and put in oxygenation and heating equipment.

[0071] ② The crabs used were crab seedlings provided by the Lishui crab breeding base. The average weight of the crab seedlings was (8g±5g). The vitality and health of the crab seedlings were almost the same. Each group treated 20 crabs. The experimental cycle was 12 days per cycle, four cycles, a total of 48 days. The bacterial agent was added once every 12 days. The bacterial agent was added in the form of a single bacterial agent directly at an inoculation rate of 0.3% (volume ratio of bacterial solution: water). The composite bacterial agent was mixed at a bacterial number ratio of 1:1 before being sprinkled and then sprinkled at an inoculation rate of 0.3% (volume ratio of composite bacterial agent: water). The CK group sprinkled an equal volume of culture medium as a control.

[0072] ③During the whole experiment, the following related indicators were measured: the content of ammonia nitrogen and nitrite in the breeding water of each group, and the growth rate of crabs in each group.

[0073] The growth rate of crabs was measured every 6 days: growth rate = (body weight on that day - initial body weight) / number of days.

[0074] After the 48-day experiment, the mortality of each group was observed, and 20 crabs in each group were dissected to determine the weight of the edible part, the protein content of the edible part, the amino acid content of the edible part, the fatty acid content of the edible part, and the ammonia nitrogen and nitrite content in the breeding water of each group. Among them:

[0075]

[0076] W: weight of the edible part in the centrifuge tube; Z: weight of the remaining crab shell + weight of the edible part in the centrifuge tube

[0077] Amino acid content of edible part = (amino acid content × volume of extract) / (weight of sample × sample volume)

[0078] Edible protein content = (protein content × volume of extract) / (sample weight × sample volume)

[0079] Fatty acid content of edible part = (fatty acid content x volume of extract) / (weight of sample x sample volume)

[0080] Table 1 Effects of water tank on crab growth rate, edible part, protein content, amino acid content and fatty acid content

[0081]

[0082] The results are shown in Table 1. Figure 4 , Figure 5 and Figure 6 As shown, the growth rates of ZT-C2+MD-7, ZT-C2 and MD-7 were significantly higher than those of the control group CK, and the crab quality-related indicators ZT-C2+MD-7, ZT-C2 and MD-7 were significantly higher than those of the control group CK. Among them, the test in the aquarium ZT-C2+MD-7 had the best effect on improving the crab quality. In addition, the ammonia nitrogen and nitrite content of ZT-C2+MD-7 were lower than those of the control group CK, indicating that ZT-C2+MD-7 can not only improve the growth rate and quality of crabs, but also has a very obvious effect on the removal of ammonia nitrogen and nitrite in the aquaculture water.

[0083] Example 6 Effects of strain combinations on physiological parameters of crabs under actual pond conditions in aquaculture centers

[0084] The experiment was conducted in Lishui, with a pond area of ​​2 mu in the Lishui crab breeding base. Three ponds of the same size, similar crab species and crab size were used for the experiment. Pond No. 16 and Pond No. 18 were the experimental groups, and Pond No. 17 was the control group. Each experimental group was added with 25 liters of ZT-C2+MD-7 mixed bacterial agent by spreading. The experimental groups added the bacterial agent once on June 24, August 8, August 29, September 16 and October 10 respectively.

[0085] Before adding the bacterial agent each time, the growth rate of the crabs was measured: growth rate = (body weight on the day - initial body weight) / number of days. The ammonia nitrogen and nitrite content in the aquaculture water was measured, and the calculation method was the same as in Example 5.

[0086] After 120 days, 20 crabs in each group were dissected to measure the weight of the edible part, the protein content of the edible part, the amino acid content of the edible part and the fatty acid content of the edible part, and the calculation method was the same as that in Example 5.

[0087] Table 2 Effects of actual crab pond culture on crab growth rate, edible part, protein content, amino acid content and fatty acid content, as well as ammonia nitrogen content and nitrite content in aquaculture water

[0088]

[0089] The results are shown in Table 2. Figure 7 , Figure 8 and Fig. 9As shown, the growth rate of the experimental group No. 16 and No. 18 ponds was significantly higher than that of the control group No. 17 pond (p < 0.05), and the experimental group was about 18% higher than the control group. This shows that the microbial agent ZT-C2 + MD-7 can increase the growth rate of crabs in actual crab ponds. In addition, compared with the control group CK, the quality of crabs in ponds No. 16 and No. 18 was significantly improved. And compared with the control, the content of ammonia nitrogen and nitrite in the experimental group was reduced by 50% and 80%, respectively. These results show that ZT-C2 + MD-7 not only improves the growth rate and quality of crabs, but also improves the water quality of aquaculture water.

Claims

1. An Issatchenkia orientalis strain ZT-C2, classified and named as Issatchenkia orientalis, with a deposit number of CGMCC NO.16008.

2. A Lactobacillus acidophilus MD-7, classified and named as: Lactobacillus acidophilus acidophilus), with the deposit number being CGMCC NO.26750.

3. The bacterial agent formed by the oriental yeast ZT-C2 according to claim 1 or the Lactobacillus acidophilus MD-7 according to claim 2; preferably, the bacterial amount of the bacterial agent is 10 7 ~10 9 CFU / mL.

4. A composite bacterial agent, characterized in that: The bacterial agent is a mixture of the oriental yeast strain ZT-C2 described in claim 1 and the Lactobacillus acidophilus MD-7 described in claim 2; preferably, the mass ratio of the mixed bacteria is 1:(0.8-1.2), preferably 1:

1.

5. The composite bacterial agent according to claim 4, characterized in that: The total bacterial count of the bacterial agent is 10 7 ~10 9 CFU / mL.

6. Use of the oriental Issatchengen strain ZT-C2 according to claim 1, the Lactobacillus acidophilus MD-7 according to claim 2, the bacterial agent according to claim 3, or the composite bacterial agent according to claim 4 or 5 in promoting the growth of crabs; preferably, use in increasing the weight and growth rate of crabs; preferably, specifically directly sprinkling the oriental Isatchengen strain ZT-C2 according to claim 1, the Lactobacillus acidophilus MD-7 according to claim 2, the bacterial agent according to claim 3, or the composite bacterial agent according to claim 4 or 5 into a crab pond or adding it to the feed eaten by crabs.

7. The use of the oriental Isatch yeast strain ZT-C2 according to claim 1, the Lactobacillus acidophilus MD-7 according to claim 2, the bacterial agent according to claim 3, or the composite bacterial agent according to claim 4 or 5 in improving the quality of crabs, preferably in increasing the content of edible protein, edible amino acids, and edible fatty acids in the crab's edible part; preferably, the oriental Isatch yeast strain ZT-C2 according to claim 1, the Lactobacillus acidophilus MD-7 according to claim 2, the bacterial agent according to claim 3, or the composite bacterial agent according to claim 4 or 5 is directly sprinkled in a crab pond or added to the feed eaten by crabs.

8. The use of the composite bacterial agent according to claim 4 or 5 in improving aquaculture water quality, preferably in reducing the content of ammonia nitrogen and nitrite in aquaculture water; preferably, specifically according to claim 4 or 5 The composite bacterial agent is directly sprinkled into the crab pond or added into the feed eaten by the crabs.

9. A method for increasing the growth rate of crabs, characterized in that: The oriental Issatchen yeast strain ZT-C2 described in claim 1, the Lactobacillus acidophilus MD-7 described in claim 2, the bacterial agent described in claim 3, or the composite bacterial agent described in claim 4 or 5 is directly sprinkled into the crab pond or added into the feed eaten by the crabs.

10. A method for improving the quality of crabs, characterized in that: The oriental Issatchen yeast strain ZT-C2 described in claim 1, the Lactobacillus acidophilus MD-7 described in claim 2, the bacterial agent described in claim 3, or the composite bacterial agent described in claim 4 or 5 is directly sprinkled into the crab pond or added into the feed eaten by the crabs.

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