Prevention and treatment of bacterial diseases in conventionally cultured fish

In recent years, due to the impact of drug residues on the export of aquatic products in China, the government has carried out a large-scale rectification of the entire fishery drug market, and has announced a large number of banned aquatic drugs, such as chloramphenicol, furazolidone, malachite green, pentachlorophenol sodium, etc. Special aquatic products because of its high economic value and a larger export market, so in all aspects of the joint efforts. The use of banned substances is well controlled. In the process of conventional fish culture, bacterial diseases occur more frequently and occur in a larger area. However, limited by its commodity value and export market, farmers often choose some old methods to prevent and control diseases, and even use some prohibited drugs, such as malachite green, furazolidone, chloramphenicol and so on. Such a control method not only seriously affects the quality of aquatic products, but also produces strong drug resistance due to long-term use of drugs, and the discharged aquaculture wastewater directly or indirectly pollutes the nature-environment, bringing serious negative effects to the sustainable development of society. Therefore, it is very necessary to explore and popularize some new methods and new drugs in the prevention and control of conventional fish diseases.

I. Fulminant haemorrhagic disease

Also known as bacterial septicemia, it is an infectious disease with the most kinds, the largest scope, the widest epidemic area, the longest epidemic season and the largest loss in China. The disease is mainly caused by two kinds of pathogenic bacteria, hygrophiles and Aeromonas milda. After the onset of the fish body surface congestion, anal redness, abdominal swelling, abdominal product has a large number of ascites and hemolysis phenomenon; intestinal no food, but there are a lot of mucus. Sick. Sometimes accompanied by exophthalmos, raised scales, gills-filament end rot and other phenomena.

This disease often occurs in fish pond water, sediment deterioration, aging, low dissolved oxygen, harmful substances in the pond. If the breeding management is not good, and then feeding moldy inferior feed, it is more likely to cause the occurrence and development of this disease.

The prevention of fulminant hemorrhagic disease should first strengthen the feeding management of breeding, feed according to the "four fixed" feeding method, and regularly use drugs for comprehensive prevention. In production, disinfectants such as dibromohydantoin, bromochlorohydantoin and natural plant extracts (Chinese herbal extracts) can be used to disinfect the water body, and then photosynthetic bacteria and other beneficial bacteria can be used to purify the bad water quality. Feed bait added immune enhancers, such as natural plant extracts without drug residues feed additives. Use boiling stone powder and nitrite degradation agent to adsorb and degrade harmful physical and chemical factors such as ammonia nitrogen and nitrite in water.

After the disease occurs, active diagnosis and treatment should be taken, first of all, whether there is parasite parasitism. If so, effective drugs should be used to kill parasites, followed by dibromohydantoin (dosage o.2ppm), bromochlorohydantoin (0.3-ppm) for disinfection of water body; secondly, photosynthetic bacteria (dosage 5ppm) or fish must (dosage 2ppm) for improvement of water quality environment; if nitrite content in water body is detected to be too high, nitrite degradation agent (0-.8 ppm) should be sprinkled at the same time for treatment; thirdly, bait is fed at the same time of sprinkling disinfectant, and 15 g of bioactive additive is added to each kilogram of feed for continuous feeding for 5 days. If the disease is more serious, should be separated by 2 days and then feeding 3 days bait can be-.

Second, enteritis

The pathogen of the disease is Aeromonas punctata, which is a conditional pathogen. This kind of pathogen exists in the intestinal tract of fish during the whole breeding process. In healthy fish, this strain is not dominant and will not cause disease, but when affected by deterioration of water quality environment, reduction of dissolved oxygen, feeding deteriorated feed, and feeding timing and quantity, the resistance of fish will decrease, so that pathogenic bacteria will be discharged into water with the feces of sick fish to pollute water quality and feed, and will be transmitted to other fish and fish species through mouth. Therefore, such diseases may occur and develop throughout the breeding cycle. When the pond water temperature is above 18℃, the disease can be epidemic, generally occurs in April to September, the sick fish generally abdominal enlargement and red-spot, anal redness, gently squeeze the abdomen that yellow mucus flows out from the anus, anatomy can be seen intestinal wall congestion inflammation, no food in the intestinal tract, only light yellow mucus, inner wall erosion.

The prevention method of enteritis is basically consistent with fulminant hemorrhagic disease, and the treatment should be combined with external elimination and internal administration. Disinfectants such as bromochlorohydantoin (0.3ppm) or dibromohydantoin (0.2ppm) can be used to disinfect aquaculture waters, and immune polysaccharides such as sea treasures (0.2%) or fish must be added to feeds (0.2). 0.4%) to enhance the immunity of fish body, continuous feeding, the disease can be basically controlled.

III. Rot gills

The pathogen was Crotacter columnaris. It is generally caused by direct contact between fish and pathogens, especially after the gills of fish are mechanically damaged. The disease can occur in the water temperature range of 15~30℃, and the higher the water temperature, the easier it is to break out. The body color of the sick fish is black, the appetite is reduced, the skin congestion and inflammation on the inner surface of the operculum can be seen when the operculum of the sick fish is opened, and the middle part is often eroded into a circular transparent small window, commonly known as "open skylight." Gills swollen, mucus increased, terminal deformity-damage. The fin edges of most of the diseased fish are pale and pale.

Prevention methods of rotten gill disease: in the operation to avoid injury to the fish body; put seedlings to be soaked in water disinfection. The pond is disinfected regularly in the breeding process, and the fish must be 2ppm or dibromohydantoin 0.3ppm-the whole pond can be sprinkled after the disease occurs.

IV. Red skin disease

The pathogen is Pseudomonas fluorescens, which is a conditional pathogen. When the fish body is injured by artificial operation such as fishing, transportation, stocking, etc. or mechanical injury, frostbite or parasitism by parasites, the pathogen takes advantage of the weakness and causes disease. The disease can be prevalent and occur all year round. Especially in spring after overwintering, it is most likely to break out (about March to May). Disease fish performance for the surface bleeding inflammation, scale shedding, fin base congestion, fin congestion or erosion was broom-like, often called "worm-fin"-, but also often accompanied by gills rot symptoms.

The control method of red skin disease is basically the same as that of rotten gill disease. The action should be light when catching and stocking, so as to avoid fish injury. Before overwintering, bromochlorohydantoin (0.3ppm) and other disinfectants should be used to disinfect the pool water and deepen the pool water to ensure that the fish body is not frostbitten. In the spring of next year, eat as early as possible to improve the immunity of fish. When using a disinfectant (dibromohydantoin or bromochlorohydantoin, etc.), kill harmful pathogens in the water, you can play a preventive effect. After the disease occurs, the method of combining pesticides with disinfectants should be adopted in time to treat the water body, and combined with internal feed drugs such as natural plant extracts for treatment. Specific operation can refer to the control method of rotten gill disease.

5. Tilapia festering disease

The pathogenic bacteria is hygrophilic bacteria, which is a conditional pathogen. It exists widely in the whole culture period and water area, but only under the condition of high density culture and improper feeding management can it cause tilapia disease. Body surface of diseased fish-congestion, loose and shedding surrounding scales. And gradually fester into a blood-red mottled depression. The focus has no specific location, and may occur in all parts of the body such as the head and trunk. Dissection of the diseased fish revealed brown liver and ink-green swollen gallbladder.

Prevention methods of tilapia festering disease: to adopt appropriate breeding density, timely enter the greenhouse to prevent frostbite, regularly use dibromohydantoin, bromochlorohydantoin and other disinfectants for disinfection, and combined with feeding fish, sea treasures and other feed bait, feed to feed some green feed, improve the immunity of fish. After the disease occurs, fish out in time and move into good water quality for temporary cultivation. At the same time, bromochlorohydantoin 0.3ppm or fish must be sprayed in the pond to disinfect the water body, and strong irritant drugs should not be used as far as possible to avoid further stimulating the focus. When the external medicine is used, it can be combined with the oral medicine bait of Zhongyunikao (o.15%) for 5~7 days.

To sum up, there are many bacterial diseases of conventional cultured fish, such as vertical scale disease, print disease, white skin disease and so on. But all pathogens have one thing in common: they are conditional pathogens. Only when the breeding density is too high, improper management causes water deterioration, fish body injury, immunity decline and so on, pathogenic bacteria multiply in large quantities and invade fish body and cause disease. Therefore, when preventing bacterial diseases, disinfectants should be used to disinfect water bodies, and then beneficial microbial preparations should be used to maintain a good water quality environment. At the same time, a series of comprehensive methods, such as using biological enzymes and polysaccharide active additives to improve the autoimmunity of fish bodies, bring higher economic benefits to culture.