Eight most common fish diseases control techniques in aquaculture

Common fish disease prevention technology

1、 Prevention of fish disease

1. Do a good job in disinfection

(1) Fish can be disinfected at a temperature above 15 ℃ by soaking in potassium permanganate solution with a concentration of 15-20mg/L for 15-20min; When the water temperature is below 15 ℃, it is advisable to consider using drugs with low irritation such as povidone iodine to disinfect the fish. Specific disinfection methods should be determined based on the microscopic examination results and pathogen types of the fish.

(2) Feed disinfection The fresh and live bait collected from the field generally contains pathogens, and is disinfected with 3% salt water for 3-5 minutes.

(3) Tool disinfection All tools shall be put into the tool disinfection tank for disinfection after use. Use 600mg/L bleaching powder solution as disinfectant, and wash the tools with clean water before use.

2. Strict quarantine system

The fish body shall be regularly sampled for inspection to understand and control the quantity of pathogens, and fish diseases, especially infectious diseases, shall be isolated, observed and treated in time to prevent the spread of diseases; New fish species can be mixed with fish in the original pond only after confirming their health.

3. Scientific management

Pay attention to the quality of feed. Long-term addition of microbial additives such as lactobacillus, bacillus subtilis and yeast in feed can improve the intestinal environment of fish; According to the niche of the cultured fish, the micro-ecological agent for improving the bottom, mainly Bacillus subtilis, should be used in time to improve the bottom quality; Micro-ecological agents such as EM bacteria, photosynthetic bacteria and enterococcus faecalis can be used for water quality improvement; Avoid fish body injury and infection caused by careless operation and transportation, and timely treat the fish body injury if any; Do not spray pesticides and other toxic substances near the fish pond to avoid damaging the fish body; The stocking density should be appropriate; Frequently patrol the pond and carefully observe the performance of the fish body to grasp the changes in the pond and take measures to improve it in time.

4. Drug prevention

In the fish disease season, drugs can be regularly sprinkled into the water and added to the feed to prevent the occurrence of fish diseases.

2、 Diagnosis of fish disease

1. Site investigation

If the fish is sick or dies, it is necessary to understand the abnormal phenomena on the surface and in the body of the sick fish and in the fish pond; Whether there is fish disease or death caused by illegal operation; Understand the speed of disease onset, the species of death and the total number of deaths at one time, the time of death, the symptoms of the sick fish, whether they jump up and down sharply and swim wildly, whether the fish are floating on the surface or sinking under the water, and what is the color change of the body surface; Check whether the water quality is normal and whether it is polluted.

2. Visual inspection

Find out the various characteristics of the diseased site or some pathogenic organisms visible to the naked eye to provide a basis for the diagnosis of fish disease.

(1) On the body surface, put the diseased fish that has just died or not died on the anatomical plate, carefully observe the head, mouth, eyes, gill cover and fin of the fish body, and check whether the skin is congested, inflamed, festered, the amount of body surface mucus, whether the base of the fin is congested, and whether the edge is normal, to see whether there are large pathogenic organisms or special symptoms.

(2) The inspection of gills and gills focuses on gill filaments. First, pay attention to whether the gill cover is open, and then open the gill cover to observe whether the color of gills is normal, whether there is much mucus, and whether the gill filaments are swollen and ulcerated. Whether there is a skylight on the inner side of the gill cover, and whether there are parasites visible to the naked eye.

(3) The viscera cut the body cavity of the diseased fish. First, observe whether the shape and color of the intestine, liver, gallbladder, gonad, spleen, swim bladder, etc. are normal, whether there is hyperemia, inflammation and large parasitic parasites. Examination of viscera: The midgut is the key point of examination. The intestines of the diseased fish should be peeled off to see whether the intestines are congested, whether there is ascites, whether there are large parasites in the body cavity, and whether there is hyperemia, inflammation and ulceration.

3. Microscopic examination

(1) Microscopic examination: Scrape the gill mucus, body surface mucus, and internal organs of the diseased fish to make a slide specimen, and observe the parasitic condition of the pathogen under the microscope.

(2) If two or more pathogens are found during the inspection of fish diseases, it is necessary to compare and analyze the intensity of infection and the degree of harm to fish caused by various pathogens, as well as the symptoms of diseased fish, in order to identify the primary and secondary causes in order to take effective prevention and control measures.

3、 Common diseases and prevention methods

1. Method of administration

(1) The fish body immersion method is to prepare a high concentration of medicine in a certain container and soak the fish body in a short time to kill the pathogen; The length of immersion time is mainly determined by the water temperature and the drug resistance of fish. Generally, when the water temperature is high, the efficacy is fast, the toxicity is strong, and the soaking time should be short; When the sick fish is weak, the immersion time should be short. When using drugs with large toxic and side effects, the immersion time should not be extended at will. Generally, within the scope of drug safety, the longer the immersion time, the better the treatment effect.

During the immersion treatment, the operator should observe the activity of the fish body and the reaction to the drug at any time to avoid poisoning the fish body and hypoxia in the container. The soaking time shall be consistent strictly to avoid affecting the efficacy or causing drug damage due to the difference of soaking time. The drugs are mainly potassium permanganate and iodine preparations. This method is mainly for cage culture.

(2) The whole-pool sprinkling method uses the medicine that is safe and effective for the fish body to dilute and evenly sprinkle it into the aquaculture water body to kill the pathogens in the fish body and water body. In order to ensure the curative effect, the water volume of the pool should be accurately measured to ensure the correct concentration. In breeding management, necessary measures should be taken to ensure the treatment effect.

(3) Internal administration method

① Mix the therapeutic drugs with adhesive and feed them in the feed, and feed them immediately after mixing.

② The drug is mixed into the feed and processed into drug pellet feed with adhesive for feeding, which is used for routine prevention and auxiliary treatment.

③ The hanging bag method is mainly used for medicine in large areas of water. The medicine is hung around the food field where fish often move to form a local area with high concentration of medicine to disinfect and treat the fish. The main drugs are bleaching powder, copper sulfate, quicklime, etc.

2. Prevention and treatment of common diseases

(1) White skin disease

Pathogen: mainly Pseudomonas albuginosa, gram-negative. It is also caused by myxococcus or flexor columnaris. This disease is not a single pathogen.

Symptoms: usually a white lesion appears at the wound or tail handle, and the dry skin rapidly spreads forward and expands, so that the dorsal fin and the base of the gluteal fin are all white and ulcerated. For serious diseased fish, the head is generally downward, the tail fin is upward, nearly perpendicular to the water surface, and soon dies. The mortality rate is very high. This disease is the most serious in summer, and at the beginning of a large area of disease, at first a group of fish floats, and white spots appear on the tail fin, much like bubble disease. Once white spots appear on the body, it may lead to the result of "total annihilation".

Prevention methods: ① Keep the water fresh and feed more high-quality feed;

② During fishing, transportation and other operations, pay attention to avoid scratching the fish body.

Treatment methods: ① Use bromochlorohydrin in the whole pool, concentration: 0.3-0.4g/m3;

② Use Chinese gallnut (Chinese medicine) to sprinkle in the whole pool, with the concentration of 2-4g/m3.

(2) Edwards disease (red head disease, head burst disease)

Pathogens: Edwardia obtuse, Edwardia channel. It is worth noting that the redhead disease of Pelteobagrus fulvidraco, which occurs in the seedling stage, usually has the concurrent infection of ciliates such as Trichotrichus, Tracheides obliquus, and Hemipterus. Therefore, the diagnosis must be comprehensive and cannot be missed.

symptom:

① External symptoms: In the early stage of the disease, the sick fish lost their appetite and swam alone, but there were no obvious symptoms on the outside. With the development of the disease, hyperemia appeared on the top of the head of the diseased fish and continued to expand. Finally, a "saddle" shaped lesion was formed in the skull between the two eyes. In severe cases, the head was perforated, the skull was cracked, and even the brain tissue was exposed. Therefore, farmers are often referred to as "outbreak disease", "split head disease", "red head disease", etc. The sick fish lost its balance before death and hung in the water in the shape of "hanging water". When stimulated, it quickly turned or swam irregularly, and then died.

② Internal symptoms: dissected diseased fish, common muscle hyperemia, a large amount of pale yellow ascites in the abdominal cavity, no food in the stomach, intestinal hyperemia, inflammation, and the stomach cavity is full of gas and light yellow water-like liquid. Liver enlargement with bleeding spots, or liver yellowish brown, spleen necrosis, mold black spots on the kidneys, pale white gill filaments, and blood loss.

Prevention method:

① On the 7th to 8th day after the fish fry are lowered into the pond, whether there is rotifer or not, use the fish medicine to control ciliates to kill the insect once.

② When the fish fry were 37.5px and 250px, the feed was added with multi-dimension (vitamin K3 powder)+Sanhuang powder+Xianmin+Qinglian powder+Fangcao Juni+compound doxycycline+Dijincao for two courses. Each course of treatment is fed once a day for 5 days, and the occurrence of red head disease is basically controlled. At present, catfish such as Pelteobagrus fulvidraco mainly use this method for prevention.

③ Other internal drugs include florfenicol, ampicillin, sulfonamides, enrofloxacin and oxytetracycline hydrochloride, generally once a day for 3-5 days each time.

Treatment:

① Microscopically check whether there are ciliates, use external insecticides, add multi-dimensional (vitamin K3 powder)+Sanhuang powder+Fangcao Xianmin+Qinglian powder+Fangcao Junni+compound doxycycline+Dijincao in the feed, and feed it once a day for 5 days.

② First, use copper sulfate+ferrous sulfate 0.7g/m3 (5:2) to kill insects, and then use chlorine dioxide water with a concentration of 0.3g/m3 to disinfect and sterilize the next day. At the same time, add antibiotics to the feed for 14-19 days. The types of antibiotics are determined by drug sensitivity tests, and generally can be used as oxytetracycline hydrochloride, tetracycline, florfenicol, ampicillin, enrofloxacin, sulfonamides, etc. The addition amount is as described.

(3) Bacterial gill rot disease

Pathogen: Flexor cylindrica.

Symptoms: The gill filaments of the diseased fish are rotten, and the focus is white spots and lumps. The inner surface of the gill cap bone is sometimes congested and turbid into a slightly round transparent area, commonly known as "open skylight". Sometimes the tip of the gill filament tissue decays, resulting in the incomplete edge of the gill filament. Due to the damage of the gill filament, the diseased fish have difficulty breathing, and often swim near the water surface in a floating head shape. After the disease is controlled, the edge of the original focus can be seen to be gradually clear, the color of the healthy part recovers, and finally the necrotic part falls off, leaving the defective part in the gill flap, which can be partially healed after rehabilitation.

Prevention method: do a good job of disinfection, and use 2% salt water to soak the fish for 5min during stocking.

Treatment:

① Sprinkle chlorine dioxide or bromochlorohydrin in the whole pond to make the water body reach the drug concentration of 0.3-0.4g/m3, and use it continuously for 2 days.

② The whole pool of Chinese nutgall is sprinkled with water concentration of 2-4g/m3.

(4) Enteritis

Pathogen: Aeromonas punctatus.

Symptoms: The abdomen of the diseased fish is swollen, the body color turns black, the abdomen shows erythema, the anus protrudes, and is red and swollen. The abdomen is opened, and there is a lot of abdominal fluid. The sick fish lost their appetite, wandered slowly away from the group, and soon died.

Prevention methods:

① Properly dilute and change fresh water frequently.

② Thoroughly clean the pond and soak the fish seeds in 2% salt water.

③ Do not feed moldy food, immerse the fresh animal feed in 2-3% salt water or add 1% salt to the feed.

④ Periodically use drugs such as allicin, Sanhuang powder and microbial additives (the main microorganism is Bacillus subtilis) to mix bait and feed.

Treatment method: take orally and sprinkle the whole pool.

① The whole pool is sprayed with 0.3g/m3 of strong chlorine essence or chlorine dioxide or 0.5g/m3 of dibromohydrin.

② Garlicin or fresh garlic juice mixed with bait can be used for oral administration; You can also feed oxytetracycline bait at the dose of 0.05g oxytetracycline per kilogram of feed for 7-10 days.

(5) Hemorrhagic edematosis

Pathogen: bacterial, not classified yet.

Symptoms: The body color of the diseased fish is yellow, mucus is increased, the skin of the throat is damaged and congested into round holes, the abdomen is swollen, the anus is swollen and turned out, the head is congested, the base of the pectoral and abdominal fins is congested, the fin is ulcerated, bile is extravasated, a large amount of blood or yellow jelly is accumulated in the abdominal cavity, the gastrointestinal tract is anorexic, the liver is earthy yellow, the spleen is necrotic, and the kidney has mildew black spots.

Prevention method:

① Regularly flush the fish pond to maintain a normal water level to prevent water quality aging and sudden changes in water temperature.

② The fishing gear used should be disinfected in time to prevent cross infection.

③ Frequently disinfect water bodies to prevent the spread of pathogens.

④ Dead fish should be disposed of in a timely manner, and should not be thrown away at will.

Treatment:

① Water disinfection: in the early stage of the disease, the whole pool is sprayed with 15-20 g/m3 of quicklime once or 1-2 g/m3 of bleach powder.

② The medicine bath is especially serious for the sick. The pond should be cleaned thoroughly and the fish should be caught in the concentrated medicine bath. For example, using 3 mg/L methylene blue for 10-15 minutes, the effect is particularly significant.

③ Internal administration of baits: the baits can be continuously administered 2-6 days after the water body is disinfected. When feeding bait, the feeding amount can be reduced by half than usual, in order to ensure the complete feeding of fish and ensure effective drug concentration. Generally, 0.5g of morpholine guanidine hydrochloride plus 0.5g of berberine hydrochloride per kilogram of feed, or 0.25g of oxytetracycline plus 0.5g of cotrimoxazole per kilogram of feed have obvious curative effect.

④ Conventional water quality management: within 2-5 days after feeding the bait, 0.2 g/m3 of bleaching powder can be sprayed on the whole pool, or 0.3 g/m3 of trichloroisocyanuric acid can be sprayed. After 7-8 days, sprinkle 25 g/m3 of quicklime slurry on the entire tank to control the pH value of the water body.

(6) Water mildew (skin mildew, white disease)

Pathogens: water mold, cotton mold, microcystis, hyphomyces, Pythium, etc.

Symptoms: At the initial stage of infection of the fish body, no abnormality can be seen with the naked eye, and microscopic examination can see that the wound is covered with water mold. When the water temperature is below 22 ℃, the water mold propagates rapidly. After two or three days, a cluster of white filamentous colonies grow in the wound, which are slightly hard and have a pricking feeling. The mycelium extends out of the body quickly and spreads horizontally to the whole body. The sick fish are in low spirits and abnormal movement. They often flock to the surface of the water or swim slowly in the upper layer of the water. Their actions are slow and their reactions are sluggish. In the severe cases, the focus is bleeding and pus, muscle decay, and bacterial and parasitic diseases are complicated. After a period of time, a large number of diseased fish die.

Cause of disease: infection caused by body surface injury. The water temperature is below 22 ℃, especially in the low temperature range of 1-15 ℃; If the water temperature rises to above 22 ℃, the sick fish can easily recover. This disease is often caused by improper handling during netting and transportation.

Prevention method:

① Clean the pond thoroughly with quicklime.

② The operation shall be careful to avoid injury to the fish.

③ Moderately dilute.

④ Do not collect injured fish as parent fish.

Treatment:

① Immerse in 2-3% salt solution for 5min, or soak in 0.5-0.6% salt water for a long time.

② 400g/m3 table salt plus 400g/m3 baking soda or 0.2-0.3g/m3 methylene blue or 10-15g/m3 quicklime, one of the above drugs is used once every other day, three times in succession, or several times in rotation, with bait and the whole pond sprinkled with insecticides and disinfectants, and the cure rate can reach 96%.

③ Use thiofloxacin, dilute every 100ml of the original solution with 20kg of water, and sprinkle it evenly in the whole pool. For general conditions, 100ml/mu · m; If the disease is serious, it can be used continuously for 2 days.

(7) White spot disease

Pathogen: melon insect with many seeds.

Symptoms: After the larvae of the melon worm immerse into the skin or gill filament tissue of the fish body, they absorb the nutrition of the fish body, causing the tissue to secrete a large amount of mucus. The naked eye can see small white spots on the body surface of the diseased fish. At the beginning of the disease, the body surface and the base of the fins are slightly red. The diseased fish stagnate at the bottom of the pool or accumulate in the corners of the fish pool, and then white spots appear and gradually increase. In serious cases, a white film forms on the body surface, the skin becomes inflamed, and refuses to eat. Most of the diseased fish begin to decay from the edge of the fins, and finally cause death.

Prevention method:

① The suitable water temperature for the melon insect is 15-25 ℃, the development stops at<10 ℃ and>28 ℃, and the larvae are easy to die when the temperature is above 28 ℃. Therefore, raising the water temperature can prevent the melon insect disease. The larvae of Meloidogyne mellifera died when they could not find the host for 24 hours, but at present, white spot disease has been found in the water temperature above 28 ℃.

② Disinfect the fish pond and fish body.

③ Prevent excessive turbidity of pool water, which is an important cause of white spot disease.

④ 0.3-0.4g per 1kg of body weight (6.0-8.0g per 1kg of feed mixed with medicine based on 5% of bait), continuous use of 1-