What are the prevention and treatment methods for the "new three diseases" of grass carp?
With the increase in farming density and the deterioration of the farming environment, grass carp farming diseases have developed from the traditional "old three diseases" (red skin disease, gill rot, enteritis, etc.) into the "new three diseases" of grass carp, namely bacterial complications (complications of red skin disease, gill rot and enteritis), viral hemorrhagic disease, and hepatobiliary syndrome. The "new three diseases" of grass carp bring greater harm to farming production, causing massive deaths of grass carp after onset.
Bacterial complications (complications of red skin disease, gill rot and enteritis)
[Causes and symptoms] The pathogens of this disease are caused by a variety of bacteria, including Aeromonas punctata f. intestinalis, Myxococcus piscicola, Pseudomonas fluorescens, etc. Fish suffering from this disease show symptoms of all three conditions at once: red skin disease, gill rot and enteritis:
The diseased fish has a darkened body color and darkened head, and swims alone away from the school; it responds slowly, the abdomen is distended, red spots are often present on both sides, there is obvious "fin erosion", the anus is red and swollen and protrudes, turning purplish red, and when the abdomen is gently pressed, yellow mucus and bloody pus flow out. When the abdomen is cut open, fluid accumulation in the abdominal cavity is visible, the intestinal wall is congested and inflamed, especially the hindgut, and the intestinal mucosal cells often ulcerate and slough off, mixing with blood to form bloody filth that fills the intestinal tract; the liver also often has red spots of congestion; the gill filaments of the diseased fish show punctate congestion, with rotting ends and exposed cartilage, causing the edges to turn white, and the gill filaments carry mucus and silt. In severe cases, the epidermis of the operculum is congested, inflamed and rotting, and the middle part is often corroded into a round transparent small window, commonly known as "open skylight"; the body surface is locally inflamed, the scales are loose and fall off, most obviously on both sides of the abdomen, the fin bases are congested, the ends rot, and water mold often parasitizes where scales have fallen off or fin rays have rotted. This disease can occur throughout the year, and is most severe especially from May to September.
[Prevention and treatment methods] Thoroughly clear and disinfect the pond, implement the "four disinfections" and "four fixings", do not directly apply unfermented animal manure, do not feed spoiled and deteriorated feed, and soak and disinfect fingerlings in 3% salt water before stocking.
[Treatment methods] Use 0.2 ppm chlorine dioxide or 0.3 ppm bromochlorohydantoin or 0.4 ppm strong chlorine powder and other disinfectants to splash over the whole pond at regular intervals; use 100 g allicin per 40 kg feed, mix with feed and feed continuously for 7 days; use 100 g enrofloxacin per 40 kg feed, mix with feed and feed continuously for 3 to 5 days, with the dosage doubled on the first day.
Hepatobiliary syndrome
[Causes and symptoms] Grass carp hepatobiliary syndrome is a common disease in grass carp farming. In the early stage of the disease, diseased fish in the pond drift and swim along the pond edge, respond slowly, and reduce their food intake. No obvious symptoms are visible on the body surface by eye, and only a small number of fish have reddened eyeballs and eye sockets and swollen gill filaments, with no parasites found under microscopic examination; dissection reveals no food in the intestinal tract, and the liver is swollen and appears white, green or yellow. These are all symptoms of hepatobiliary syndrome. In severe cases, the liver is pulpy and adheres to the intestinal mucosa and fat, filling the thoracic cavity, and the gallbladder is sometimes enlarged and blackened, sometimes absent, with severe ascites. After the disease has been present for some time, the number of dead fish surges; the causes of this disease are relatively complex. Feeding deteriorated feed, feed with excessive fat content, or long-term feeding of feed containing olaquindox, as well as pollution of the fish-rearing water body by copper, ammonia and other substances, can all trigger liver disease.
[Prevention and treatment methods] Pay attention to reasonable stocking density, do not feed spoiled and deteriorated feed, do not directly apply unfermented animal manure, frequently add fresh water or use biological agents to improve water quality, frequently remove feed residues, establish an inspection system for fish feed, keep feed fresh, and prevent the oxidation of protein and fat in feed.
[Treatment methods] Use 0.2 ppm chlorine dioxide or 0.3 ppm bromochlorohydantoin or 0.4 ppm strong chlorine powder and other disinfectants to splash over the whole pond at regular intervals; use 100 g Gandanning + 100 g allicin mixed with 40 kg feed to make medicated bait, and feed continuously for 5 to 7 days.
Viral hemorrhagic disease
[Causes and symptoms] In the early stage of the disease, observed from the outside, the diseased fish shows mild congestion in the oral cavity, abdomen, operculum, eye sockets, fin rays and both sides of the body. When the abdominal cavity is cut open, a small amount of food is still seen in the intestinal tract. As the disease progresses, the above-mentioned body surface congestion worsens, the flesh shows hemorrhagic symptoms, the area around the eye sockets is congested, the eyeballs protrude, and the abdomen is distended and red and swollen. When the abdominal cavity is cut open, because the internal organs are damaged, yellow or red ascites accumulates in the abdominal cavity, the liver, spleen and kidney are enlarged, and the intestinal wall is congested, inflated and contains no food. The gills are grayish white, showing anemia, and are sometimes purple and swollen, and in severe cases the ends of the gill filaments rot.
[Epidemiology] From March to April, the symptoms of inflamed and congested body surface appearing in diseased fish are most severe on the head, mouth, operculum, eye sockets, both sides of the body surface, below the pelvic fins and the caudal peduncle, etc. Some diseased fish show exophthalmos, anemic gills, and internal organs with varying degrees of inflammation, and sometimes the intestinal tract is also seen to be inflated and distended. After May, the symptoms of diseased fish are mostly congestion and inflammation under the lower edge of the operculum, at the fin bases and in the internal organs, and sometimes the flesh of the oral cavity is also congested and inflamed at the same time. This disease is widely prevalent in grass carp farming. It can occur at water temperatures between 9 and 36°C, and is most severe at 28°C, often causing enormous economic losses. Therefore, this is an epidemic disease with the widest prevalence, the longest season and the greatest harm.
[Prevention and treatment methods] Thoroughly clear and disinfect the pond, implement the "four disinfections" and "four fixings", and frequently add fresh water or use biological agents to improve water quality.
Treatment methods: Use 0.2 ppm chlorine dioxide or 0.3 ppm bromochlorohydantoin or 0.4 ppm strong chlorine powder and other disinfectants to splash over the whole pond at regular intervals; orally administer 100 g 10% enrofloxacin + 200 g Sanhuang powder mixed with 40 kg feed, and feed continuously for 5 to 7 days.