Prevention and treatment of common bacterial diseases of farmed fish

1 fulminant hemorrhagic disease

Bacterial septicemia, also known as bacterial septicemia, is an infectious disease with the largest number of species, the largest range, the widest epidemic area, the longest epidemic season and the greatest loss of fish in China. The disease is mainly caused by two pathogens: Aeromonas hydrophila and Aeromonas aeruginosa. After the disease, the body surface of the fish is congested, the anus is red and swollen, the abdomen is enlarged, there is a large amount of ascites and hemolysis in the abdominal cavity, and there is no food in the intestine. but there's a lot of mucus. The disease is sometimes accompanied by exophthalmos, scale upright, Gill filament end rot and so on.

The disease often occurs in fish ponds with deteriorating water, aging, low dissolved oxygen and high levels of harmful substances. If the breeding management is poor, coupled with the feeding of moldy low-quality feed, it is more likely to cause the occurrence and development of the disease.

For the prevention of fulminant hemorrhagic disease, first of all, we should strengthen the feeding management and feed according to the "Siding" feeding method. Regular use of drugs for comprehensive prevention, production can use dibromohydantoin, bromochlorohydantoin, natural plant extracts (Chinese herbal medicine extracts) and other disinfectants to disinfect the water body, and then purify the bad water quality by photosynthetic bacteria. Zeolite, nitrite and other degradants are used to absorb and degrade harmful physical and chemical factors such as ammonia nitrogen and nitrite in water, and immune enhancers are added to feed.

Active diagnosis and treatment should be taken after the occurrence of the disease. First of all, diagnose whether there are harmful parasites. If effective drugs should be taken to kill parasites, then use dibromohydantoin (0.2 mg/L) and bromochlorohydantoin (0.3 mg/L) to disinfect the water, and then use photosynthetic bacteria (5 mg/L) or Yubide (2 mg/L) to improve the water quality environment. If the nitrite content in the water is too high, it should be treated with nitrite degradation agent (0.8 mg/L) in time. At the same time of spraying disinfectant, the bait was fed with 1.5 g bioactive additive per kilogram of feed for 5 consecutive days. if the disease was serious, the bait should be given every 2 days and 3 days.

2 enteritis

The pathogen of the disease is intestinal type Aeromonas punctata, which is a conditional pathogen. This kind of bacteria exists in the intestinal tract of fish during the whole culture process. In healthy fish, this strain is not dominant and will not cause disease, but when affected by the deterioration of water quality, the decrease of dissolved oxygen, the feeding of deteriorated feed and improper bait, the resistance of the fish decreases, so that the pathogen is discharged into the water with the feces of the diseased fish to pollute the water quality and feed and spread to other fish by mouth. Therefore, this kind of disease may occur and develop in the whole culture cycle. When the water temperature in the pond is above 18 ℃, the disease can be prevalent, and generally occurs from April to September. The diseased fish generally have abdominal enlargement, erythema, anal redness and swelling, and gently squeeze the abdomen with yellow mucus flowing out of the anus; anatomy shows that the intestinal wall is congested and inflamed, there is no food in the intestine, only light yellow mucus, and the inner wall is rotten.

The preventive method of enteritis is basically the same as that of fulminant hemorrhagic disease, and the method of external elimination and internal administration should be taken in the treatment. Disinfectants such as bromochlorohydantoin (0.3 mg/L) or dibromohydantoin (0.2 mg/L) can be used to disinfect aquaculture waters, and immune polysaccharides Haizhenbao (0.2%) or Yubide (0.2% 0.4%) can be added to the feed to enhance the immunity of fish, and the disease can be basically controlled by continuous feeding.

3Gill rot disease

The pathogen is flex columnar bacilli. It is generally caused by direct contact between fish and pathogenic bacteria. Especially when the gills of fish are mechanically damaged, they are more likely to be infected. The disease can occur in the range of 15-30 ℃ water temperature, and the higher the water temperature is, the easier it is to break out. Diseased fish body color is black, loss of appetite, open the operculum of diseased fish to see the inner surface of the skin hyperemia and inflammation, the middle part is often rotten into a round transparent window, commonly known as "open skylight". The Gill filaments are red and swollen, the mucus is increased, the end is defective, and the fin edges of most diseased fish turn white and pale.

Prevention of Gill rot disease. Be brisk in operation to avoid injury to the fish, soak and disinfect the seedlings with potions. The pond was disinfected regularly in the process of culture, and the whole pond was sprinkled with fish must (2 mg/L) or dibromohydantoin (0.3 mg/L).

4. Red skin disease

The pathogen is often Pseudomonas fluorescens, which is a conditional pathogenic bacteria. when the fish is injured by manual operation, such as fishing, transportation, stocking, mechanical injury or parasitism, the pathogen takes advantage of the deficiency to cause the disease. The disease can occur throughout the year, especially after overwintering, the disease is most likely to break out in spring (about 3 ~ 5 months). The diseased fish are characterized by bleeding on the body surface, inflammation, scale exfoliation, congestion at the base of the fins, hyperemia or erosion of the fins, which are often called "fin decay", and are often accompanied by symptoms of rotten gills.

The prevention and control methods of red skin disease are basically the same as Gill rot disease. When catching and rearing, the action should be light to avoid fish injury. Before overwintering, disinfectants such as bromochlorohydantoin (0.3 mg/L) should be used to disinfect the pond water and deepen the water level. At the same time, the use of disposable disinfectants (dibromohydantoin or bromochlorohydantoin, etc.) to kill harmful pathogens in the water can have a preventive effect. After the occurrence of the disease, the combination of insecticides and disinfectants should be used in time to treat the water, and combined with internal administration of feed drugs, such as natural plant extracts for treatment, the specific operation can refer to the prevention and treatment of Gill rot disease.

To sum up, there are many bacterial diseases in conventional farmed fish, such as vertical scale disease, printing disease, white skin disease and so on. All pathogens have one thing in common: they are conditional pathogens. Only when the culture density is too high and improper management leads to the deterioration of water quality, injury of fish, decrease of immunity and so on, the pathogenic bacteria multiply in large numbers and invade the fish. Therefore, in the prevention of bacterial diseases, disinfectants should be used to disinfect the water quality, and then beneficial microbial preparations should be used to maintain a good water quality environment, and at the same time, active additives of biological enzymes and polysaccharides should be used together with a series of comprehensive methods to improve the self-immunity of fish and bring effective economic benefits to culture.