Plant extract composition for enhancing disease resistance of fry and application of plant extract composition

Abstract

The invention discloses a plant extract composition for enhancing disease resistance of fish fries and application of the plant extract composition, and belongs to the technical field of aquaculture. The plant extract composition for enhancing the disease resistance of the fry is prepared from the following raw materials in parts by mass: 10 to 20 parts of macleaya cordata extract, 15 to 25 parts of gallnut extract, 10 to 20 parts of red-knees herb extract, 5 to 15 parts of hawthorn fruit extract and 5 to 10 parts of liquorice root extract. According to the plant extract composition provided by the invention, five extracts of macleaya cordata, gallnut, red-knees herb, hawthorn and liquorice are scientifically compounded, so that a remarkable synergistic interaction effect is generated, the non-specific immune function of fry can be effectively regulated, and the disease resistance and stress resistance of the fry are improved. Especially for pelteobagrus fulvidraco fries, the composition can significantly repair and protect fragile intestinal tract and gill mucosa tissues of the pelteobagrus fulvidraco fries while efficiently preventing and controlling bacterial and parasite infection.

Description

Technical Field

[0001] This invention relates to the field of aquaculture technology, and in particular to a plant extract composition for enhancing the disease resistance of fish fry and its application. Background Technology

[0002] Aquaculture is a vital component of the global food supply chain, providing humans with a large amount of high-quality animal protein. Fish farming is the leading sector within aquaculture. However, with the widespread adoption of intensive, high-density farming methods, the farming environment is deteriorating, making it easy for various pathogens (such as bacteria, viruses, and parasites) to proliferate and spread, leading to frequent fish diseases and causing significant economic losses to the aquaculture industry. Among the various growth stages of fish, the fry stage is the most vulnerable and sensitive period in their life cycle. Fry have underdeveloped immune systems and immature organ functions, making them extremely susceptible to pathogens and with low tolerance to external environmental stimuli (including drugs). Therefore, the fry stage is a high-risk period for disease outbreaks; once an outbreak occurs, it often results in large-scale mortality within a short period, with a sharp decline in survival rates. Therefore, how to safely and effectively enhance the non-specific immunity of fish fry and improve their disease resistance is a pressing technical challenge in the aquaculture industry.

[0003] To address this challenge, the industry has long explored and applied various methods to enhance the disease resistance of fish fry. However, existing technologies have significant limitations, particularly in balancing disease resistance with safety. For example, in traditional aquaculture, farmers typically use chemical disinfectants or antibiotics for treatment and prevention to prevent fish diseases. While these substances can kill pathogens to some extent, they easily lead to drug residues and food safety issues. Antibiotics can remain in fish and be transmitted to humans through the food chain, posing a serious threat to public health. Furthermore, fish fry have immature metabolic organs such as the liver and kidneys, making them highly sensitive to drugs. Many antibiotics and chemical disinfectants have significant hepatotoxicity and nephrotoxicity, easily causing organ damage to fry even at conventional dosages, inhibiting their growth and development, and even directly leading to death, significantly reducing fry survival rates. In addition, while killing pathogens, chemical drugs also indiscriminately kill beneficial microorganisms in the water and fish intestines, disrupting the microecological balance upon which they depend for survival and further weakening the fry's own immunity. Long-term use of the same drug can create selective pressure on pathogens, leading to the emergence of drug-resistant bacteria and making fish disease treatment more difficult.

[0004] Given the various drawbacks of chemical drugs, some researchers have turned their attention to natural, green traditional Chinese medicine. Some plants with heat-clearing, detoxifying, and pathogen-fighting properties have been tested for use in aquaculture. However, the application of this technology also faces challenges. When these components are used on fish fry, their effectiveness in preventing and treating diseases is often poor, or they cannot be effectively absorbed, resulting in weak and unstable immune-enhancing effects, failing to provide sufficient protection under severe disease challenges. Furthermore, most current research focuses on the simple use of plant powders or decoctions. This extensive application method may lead to a complex variety of active ingredients, unstable content, and low bioavailability. Moreover, plant raw materials are complex in composition; in addition to the active ingredients, they may contain unknown components that have toxic side effects on fish fry. For example, some plants contain saponins and alkaloids, which may be harmless to normal fish at low doses, but when used on fish fry with fragile immune systems, improper formulation or slightly high concentrations can produce strong irritation, damaging the gills and intestinal mucosa, causing stress responses, suppressing the immune system, leading to decreased feed intake, stunted growth, or even death. This unpredictable toxicity risk greatly limits its widespread application in the critical stages of fish fry development. Summary of the Invention

[0005] The purpose of this invention is to provide a plant extract composition for enhancing the disease resistance of fish fry and its application, thereby addressing the aforementioned problems in the prior art. The plant extract composition provided by this invention, through the scientific compounding of five extracts—*Polygonum hydropiper*, *Gnaphalium affine*, *Polygonum hydropiper*, hawthorn, and licorice—produces a significant synergistic effect, effectively regulating the non-specific immune function of fish fry and enhancing their disease resistance and stress resistance. Particularly for yellow catfish fry, this composition can effectively prevent and control bacterial and parasitic infections while significantly repairing and protecting their fragile intestinal and gill mucosa.

[0006] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention: provides a plant extract composition for enhancing the disease resistance of fish fry, wherein the raw materials, by mass parts, include: 10-20 parts of *Gnaphalium affine* extract, 15-25 parts of *Gnaphalium affine* extract, 10-20 parts of *Polygonum hydropiper* extract, 5-15 parts of *Crataegus pinnatifida* extract, and 5-10 parts of *Glycyrrhiza uralensis* extract.

[0007] Preferably, the preparation method of the *Eupatorium fortunei* extract includes the following steps: Take *Gynostemma pentaphyllum* plants, crush them, enzymatically hydrolyze them in ethanol solution, then reflux extract them, concentrate the filtrate to obtain the *Gynostemma pentaphyllum* extract.

[0008] Preferably, the solvent is an ethanol solution when preparing gallnut extract; the solvent is an ethanol solution when preparing Polygonum hydropiper extract; the solvent is an ethanol solution when preparing hawthorn extract; and the solvent is an ethanol solution when preparing licorice extract.

[0009] Preferably, the preparation method of the gallnut extract includes the following steps: Take gallnuts, crush them, enzymatically hydrolyze them in ethanol solution, then reflux extract them, concentrate the filtrate to obtain the gallnut extract.

[0010] Preferably, the preparation method of the Polygonum hydropiper extract includes the following steps: Take the whole Polygonum hydropiper, crush it, enzymatically hydrolyze it in ethanol solution, then reflux extract it, concentrate the filtrate to obtain the Polygonum hydropiper extract.

[0011] Preferably, the preparation method of the hawthorn extract includes the following steps: Hawthorn fruit was crushed, enzymatically hydrolyzed in ethanol solution, then refluxed for extraction, and the filtrate was concentrated to obtain the extract of *Hedyotis diffusa*.

[0012] Preferably, the method for preparing the licorice extract includes the following steps: Take licorice root, crush it, enzymatically hydrolyze it in ethanol solution, then reflux extract it, concentrate the filtrate to obtain the licorice extract.

[0013] Preferably, the raw materials, by mass parts, are: 15 parts of *Gnaphalium affine* extract, 20 parts of *Gnaphalium affine* extract, 15 parts of *Polygonum hydropiper* extract, 10 parts of hawthorn extract, and 8 parts of licorice extract.

[0014] The second technical solution of the present invention provides a method for preparing the above-mentioned plant extract composition for enhancing the disease resistance of fish fry, comprising the following steps: The raw materials are mixed and spray-dried to obtain the plant extract composition.

[0015] The third technical solution of the present invention provides the application of the above-mentioned plant extract composition for enhancing the disease resistance of fish fry in the preparation of feed for enhancing the disease resistance of fish fry.

[0016] Preferably, the fish fry are yellow catfish fry.

[0017] The fourth technical solution of the present invention provides a method for enhancing the disease resistance of yellow catfish fry by incorporating the above-mentioned plant extract composition for enhancing the disease resistance of fry into the feed of yellow catfish fry.

[0018] Preferably, the amount of the plant extract composition for enhancing the disease resistance of fish fry added to the feed is 0.3-0.6 wt%.

[0019] The technical principle of this invention is as follows: This invention primarily focuses on experimental research into the disease resistance of yellow catfish fry. Due to their scaleless body surface and preference for bottom-dwelling behavior, yellow catfish are more susceptible to bacterial and parasitic infections, resulting in higher disease incidence and greater difficulty in disease control under conventional rearing methods. Furthermore, because yellow catfish are highly resistant to many common medications and have stringent water quality requirements, the types of drug ingredients must be strictly controlled.

[0020] The extract of *Gnaphalium affine* of this invention contains sanguinarine, a benzophenanthridine alkaloid with antibacterial, antiparasitic, and anti-inflammatory activities. It can disrupt the cell membrane structure of pathogenic microorganisms and inhibit their proliferation. Unlike traditional chemical drugs, the *Gnaphalium affine* extract added in this invention is less likely to induce drug resistance, and it is metabolized rapidly in vivo, resulting in a low risk of residue.

[0021] However, research revealed that *Polygonum hydropiper* alone is significantly irritating to the intestines of fish fry, and even when added as an extract, its impact on fry survival rates remains unaffected. This invention, by synergistically adding *Polygonum hydropiper* extract with *Galla chinensis* and *Polygonum hydropiper*, achieves anti-inflammatory and mucosal protective effects, helping to protect the intestines of yellow catfish and effectively neutralizing its potential irritation.

[0022] The Polygonum hydropiper extract added in this invention has good anti-inflammatory, analgesic and tissue repair effects, which can effectively reduce inflammation of gills, intestinal mucosa and other tissues caused by environmental stress or pathogen infection in fish fry and accelerate tissue repair.

[0023] Gallnut extract is rich in tannins, which have antibacterial, antiviral, and biofilm-forming effects. In fish fry, it can bind to intestinal mucosal proteins to form a protective film, reducing pathogen invasion. At the same time, tannins themselves have a direct inhibitory effect on a variety of aquatic pathogens (such as Aeromonas).

[0024] The potent antibacterial and intestinal protective effects of gallnut, combined with the antibacterial and antiparasitic effects of scutellaria barbata and the anti-inflammatory and repairing effects of Polygonum hydropiper, have a synergistic effect, making it especially suitable for enhancing the disease resistance of yellow catfish fry with no scales on their body surface and a fragile intestine.

[0025] In contrast, if the preferred Polygonum hydropiper extract and Galla chinensis extract of this invention are replaced with other ingredients, such as Eucommia ulmoides extract, the current protective effect of this invention cannot be achieved, or other negative effects may be introduced, leading to a decrease in the survival rate of fish fry.

[0026] Hawthorn extract can promote the secretion of digestive juices in fish fry, improve feed conversion rate, and enhance appetite. The stomach-strengthening effect of hawthorn can effectively counteract the potential side effects of tannins in gallnuts, such as slowed gastrointestinal motility, ensuring that fish fry receive intestinal protection without affecting their feeding and growth.

[0027] The added licorice extract has anti-stress and liver-protective effects, which can enhance the fish fry's tolerance to environmental changes (such as temperature differences and oxygen levels) and alleviate the slight toxic side effects that other ingredients may cause, thus significantly improving the overall safety of the composition.

[0028] Compared to other application methods, preparing *Gynostemma pentaphyllum* into a plant extract has a lower impact on the survival rate of fish fry. This is likely because preparing *Gynostemma pentaphyllum* into a plant extract reduces its toxicity to the fish fry. Furthermore, *Gynostemma pentaphyllum* itself is bitter, and the crushed herb powder has a rough texture and a strong herbal odor, which can easily lead to poor palatability and fish fry refusing to eat.

[0029] Existing methods of applying traditional Chinese medicine often involve simple grinding, resulting in complex components, uncontrollable toxicity, and poor palatability, which can easily lead to fish fry refusing to eat. However, the plant extract composition designed in this invention solves these problems through the optimization of raw material types and the improvement of preparation process, making it a fish feed additive with good application effects.

[0030] The amount of plant extract added in this invention is the result of comprehensive consideration. If the amount added is too high, it will also affect the survival rate of fish fry.

[0031] The beneficial technical effects of the present invention are as follows: The plant extract composition provided by this invention, through the scientific compounding of five extracts—Gynostemma pentaphyllum, Gallnut, Polygonum hydropiper, Crataegus pinnatifida, and Glycyrrhiza uralensis—produces a significant synergistic effect, effectively regulating the non-specific immune function of fish fry and enhancing their disease resistance and stress resistance. Specifically for yellow catfish fry, this composition can effectively prevent and control bacterial and parasitic infections while significantly repairing and protecting their fragile intestinal and gill mucosa. The components complement each other, providing potent antibacterial and anti-inflammatory effects while also harmonizing and detoxifying, ensuring good feeding and healthy growth for the fry. The composition of this invention is made from natural ingredients, without the use of any chemical antibiotics or drugs, has no toxic side effects, and leaves no harmful residues. It can fundamentally improve the survival rate of fish fry, providing a safe, efficient, and green solution for solving the problem of disease control in the fry stage.

[0032] The plant extract composition of the present invention can be administered to fish along with fish feed, which can enhance the fish’s resistance through internal factors, improve the survival rate of fish fry, and minimize the occurrence of diseases.

[0033] After applying the plant extract composition designed in this invention, yellow catfish can still have a good survival rate even at high stocking densities, thereby improving the economic benefits of aquaculture. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0035] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. It should be noted that any aspects of this invention not described in detail are conventional practices in the art and are not the focus of this invention.

[0037] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0038] Existing treatments for enhancing fish fry disease resistance still have certain drawbacks. On the one hand, while chemical drugs and antibiotics reduce disease incidence, their toxic side effects on fish fry, negative impacts on survival rates, and harm to the environment and food safety make them incompatible with modern healthy aquaculture concepts. On the other hand, while natural plant-based solutions have the potential to be green and safe, most currently suffer from problems such as poor efficacy, unstable components, or potential toxicity risks, and similarly cannot stably and efficiently enhance the disease resistance of fish fry while ensuring high survival rates. Based on this, the present invention designs a plant extract composition for enhancing the disease resistance of fish fry.

[0039] All raw materials used in the following embodiments and comparative examples of the present invention are commercially available products.

[0040] Example 1 A plant extract composition, wherein the raw materials, by mass parts, are: 15 parts of *Gnaphalium affine* extract, 20 parts of *Gnaphalium affine* extract, 15 parts of *Polygonum hydropiper* extract, 10 parts of hawthorn extract, and 8 parts of licorice extract.

[0041] The preparation method of the extract of *Eupatorium fortunei* used is as follows: Take the dried whole herb of *Boletus lucidum*, pulverize it, and pass it through a 20-mesh sieve. Weigh the powder, add 8 times its weight of 60 vol% ethanol solution, adjust the pH to 5.0 with dilute hydrochloric acid, add 1.0% of the raw material weight of a compound enzyme (cellulase:pectinase = 1:1), and enzymatically hydrolyze at 50℃ for 2 hours. After enzymatic hydrolysis, raise the temperature to 60℃ and reflux extract at an ultrasonic frequency of 30 kHz for 0.5 hours, then filter. Add 6 times its weight of 60 vol% ethanol to the residue and repeat the extraction once under the above conditions, combining the filtrates. Purify the filtrate by filtration through a ceramic membrane, and concentrate it under vacuum at 50℃ to a thick paste with a relative density of 1.15-1.20, thus obtaining the final product.

[0042] The preparation method of the Polygonum hydropiper extract used is as follows: Take dried whole Polygonum hydropiper, pulverize it, and pass it through a 20-mesh sieve. Weigh the powder, add 10 times its weight of 60 vol% ethanol solution, adjust the pH to 5.0 with dilute hydrochloric acid, add 1.0% of the raw material weight of a compound enzyme (cellulase:pectinase = 1:1), and enzymatically hydrolyze at 50℃ for 2 hours. After enzymatic hydrolysis, raise the temperature to 80℃ and reflux for 1.5 hours, then filter. Add 7 times its weight of 60 vol% ethanol to the residue and repeat the extraction once under the above conditions, combining the filtrates. Purify the filtrate by filtration through a ceramic membrane, and concentrate it under vacuum at 60℃ to a thick paste with a relative density of 1.10-1.15, thus obtaining the final product.

[0043] The preparation method of the gallnut extract used is as follows: Take dried gallnuts, pulverize them, and pass them through a 30-mesh sieve. Weigh the powder, add 10 times its weight of 50 vol% ethanol solution, adjust the pH to 6.0 with dilute hydrochloric acid, add 1.0% of the raw material weight of a compound enzyme (cellulase:pectinase = 1:1), and enzymatically hydrolyze at 45℃ for 1.5 hours. After enzymatic hydrolysis, raise the temperature to 70℃ and reflux for 2 hours, then filter. Add 7 times its weight of 50 vol% ethanol to the residue and repeat the extraction once under the above conditions, combining the filtrates. Purify the filtrate by filtration through a ceramic membrane, and concentrate it under vacuum at 55℃ to a thick paste with a relative density of 1.25-1.30, thus obtaining the final product.

[0044] The preparation method of the hawthorn extract used is as follows: Take dried hawthorn fruit, crush it, and pass it through a 40-mesh sieve. Weigh the powder, add 8 times its weight of 50 vol% ethanol solution, adjust the pH to 4.0 with dilute hydrochloric acid, add 1.0% of the raw material weight of a compound enzyme (cellulase:pectinase = 1:1), and enzymatically hydrolyze at 50℃ for 2 hours. After enzymatic hydrolysis, raise the temperature to 80℃ and reflux for 1 hour, then filter. Add 6 times its weight of 50 vol% ethanol to the residue and repeat the extraction once under the above conditions, combining the filtrates. Purify the filtrate by filtration through a ceramic membrane, and concentrate it under vacuum at 60℃ to a thick paste with a relative density of 1.15-1.20, thus obtaining the final product.

[0045] The preparation method of the licorice extract used is as follows: Take dried licorice root, pulverize it, and pass it through a 20-mesh sieve. Weigh the powder, add 10 times its weight of 60 vol% ethanol solution, adjust the pH to 7.5 with dilute hydrochloric acid, add 1.0% of the raw material weight of a compound enzyme (cellulase:pectinase = 1:1), and enzymatically hydrolyze at 50℃ for 2 hours. After enzymatic hydrolysis, raise the temperature to 85℃ and reflux for 2 hours, then filter. Add 8 times its weight of 60 vol% ethanol to the residue and repeat the extraction once under the above conditions, combining the filtrates. Purify the filtrate by filtration through a ceramic membrane, and concentrate it under vacuum at 60℃ to a thick paste with a relative density of 1.15-1.20, thus obtaining the final product.

[0046] The specific preparation steps are as follows: Mix all the raw materials evenly, and then spray dry to obtain this plant extract composition.

[0047] Example 2 The only difference from Example 1 is that it consists of the following parts by weight of raw materials: 18 parts of *Gnaphalium affine* extract, 14 parts of *Gnaphalium affine* extract, 17 parts of *Polygonum hydropiper* extract, 12 parts of *Crataegus pinnatifida* extract, and 7 parts of *Glycyrrhiza uralensis* extract.

[0048] Example 3 The only difference from Example 1 is that it consists of the following parts by weight of raw materials: 16 parts of *Gnaphalium affine* extract, 10 parts of *Gnaphalium affine* extract, 19 parts of *Polygonum hydropiper* extract, 10 parts of *Crataegus pinnatifida* extract, and 8 parts of licorice extract.

[0049] Comparative Example 1 The only difference from Example 1 is that the addition of the extract of *Botrytis cinerea* is omitted and an equal mass of *Botrytis cinerea* powder is added. The preparation method of *Botrytis cinerea* powder is as follows: take dried whole *Botrytis cinerea* herb and crush it to pass through a 120-mesh sieve (larger particles will affect the feeding of fish fry).

[0050] Comparative Example 2 The only difference from Example 1 is that the addition of gallnut extract is omitted and an equal mass of Eucommia ulmoides extract is added. The preparation method of Eucommia ulmoides extract is as follows: Take dried Eucommia ulmoides leaves, pulverize them, and pass them through a 20-mesh sieve. Weigh the powder, add 10 times its mass of 60 vol% ethanol solution, adjust the pH to 6.0 with dilute hydrochloric acid, add 1.0% of the raw material mass of a compound enzyme (cellulase: pectinase = 1:1), and enzymatically hydrolyze at 45°C for 1.5 hours. After enzymatic hydrolysis, raise the temperature to 70°C, reflux for 2 hours, and filter. Add 7 times its mass of 60 vol% ethanol to the residue, and repeat the extraction once under the above conditions, combining the filtrates. The filtrate is purified by filtration through a ceramic membrane and concentrated under vacuum at 55°C to a thick paste with a relative density of 1.15-1.20, thus obtaining the extract.

[0051] Comparative Example 3 (Galla chinensis extract and Polygonum hydropiper extract omitted) The only difference from Comparative Example 2 is that the addition of Polygonum hydropiper extract was omitted and an equal mass of Eucommia ulmoides extract was added.

[0052] Comparative Example 4 The only difference from Example 1 is that the addition of Polygonum hydropiper extract is omitted and an equal mass of Galla chinensis extract is added.

[0053] Comparative Example 5 The only difference from Example 1 is that the addition of hawthorn extract is omitted.

[0054] Comparative Example 6 The only difference from Example 1 is that the addition of licorice extract is omitted.

[0055] Effect verification Aquaculture trials were conducted under the following conditions: The stocking and rearing of yellow catfish fry were carried out in accordance with the "Technical Regulations for the Conservation and Breeding of Yellow Catfish (DB3404 / T16-2024)". Before stocking, pond cleaning, insecticide application (using bleaching powder and copper sulfate), detoxification, and rotifer cultivation were carried out according to local farming practices. Then, the fry were stocked (stocking density of 15,000-17,000 fry per mu, fry size of 0.8-1cm, all-male No. 1 variety). Feeding began 3 days after stocking. The feed met the standards of "Compound Feed for Yellow Catfish (NY / T3000-2016)" and included 0.5 wt% of the products from each example and comparative example. A blank control (CK group) was established with the treatment group without other components, and a positive control was established with the treatment group containing 0.1 wt% oxytetracycline + 0.1 wt% matrine. Other management methods were carried out according to local practices. After 30 days of rearing, the overall incidence rates of diseases such as saprolegniasis, bacterial septicemia, parasitic diseases, and ascites were statistically analyzed, and the survival rate and weight gain rate of the fry were calculated. The test results are shown in Table 1.

[0056] The formula for calculating the overall morbidity rate is: Overall morbidity rate (%) = Total number of diseased fish ÷ Total number of fish fry stocked × 100% The survival rate is calculated using the following formula: Survival rate (%) = Number of surviving fish ÷ Total number of fish fry released × 100% The formula for calculating the weight gain rate is: Weight gain rate (%) = (Fish weight in other treatment groups - Fish weight in the control group) ÷ Total fish weight in the control group × 100% Table 1 The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A plant extract composition for enhancing the disease resistance of fish fry, characterized in that, Raw materials, by mass parts, include: 10-20 parts of *Gnaphalium affine* extract, 15-25 parts of *Gnaphalium affine* extract, 10-20 parts of *Polygonum hydropiper* extract, 5-15 parts of *Crataegus pinnatifida* extract, and 5-10 parts of *Glycyrrhiza uralensis* extract.

2. The plant extract composition for enhancing disease resistance in fish fry according to claim 1, characterized in that, The preparation method of the extract of *Euphorbia lathyris* includes the following steps: Take *Gynostemma pentaphyllum* plants, crush them, enzymatically hydrolyze them in ethanol solution, then reflux extract them, concentrate the filtrate to obtain the *Gynostemma pentaphyllum* extract.

3. The plant extract composition for enhancing disease resistance in fish fry according to claim 1, characterized in that, The raw materials, by mass parts, are: 15 parts of *Gnaphalium affine* extract, 20 parts of *Gnaphalium affine* extract, 15 parts of *Polygonum hydropiper* extract, 10 parts of hawthorn extract, and 8 parts of licorice extract.

4. A method for preparing a plant extract composition for enhancing the disease resistance of fish fry according to any one of claims 1-3, characterized in that, Includes the following steps: The raw materials are mixed and spray-dried to obtain the plant extract composition.

5. The use of the plant extract composition for enhancing the disease resistance of fish fry according to any one of claims 1-3 in the preparation of feed for enhancing the disease resistance of fish fry.

6. The application according to claim 5, characterized in that, The fish fry mentioned are yellow catfish fry.

7. A method for enhancing the disease resistance of yellow catfish fry, characterized in that, The plant extract composition according to any one of claims 1-3 for enhancing the disease resistance of yellow catfish fry is incorporated into the feed.

8. The method according to claim 7, characterized in that, The plant extract composition used to enhance the disease resistance of fish fry is incorporated into the feed at a rate of 0.3-0.6 wt%.

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