There is a kind of harmful bacteria called Vibrio, which is a headache for farmers in aquaculture, and Vibrio can cause early liver and pancreatic necrosis, jejunal and empty stomach, stealing death and other terminal diseases in the process of shrimp farming. In the hot summer, the amount of feeding is large, the water quality is easy to deteriorate, and it is easy to induce vibriosis.
Classification of Vibrio bacteria that shrimp are susceptible to infection
Vibrio is an anaerobic bacterium with a short body, curved into an arc, and a flagella on the tail. The main bacteria of shrimp are: Vibrio algae, Vibrio parahaemolyticus, Vibrio Harvey's, Vibrio cholerae, etc.
1. Vibrio algae:
Gram-negative bacteria, tolerable pH range of 6-8.5, salinity range of 5 ‰-50 ‰, 0% fresh water does not grow, can use monosaccharides or oligosaccharides, in the TCBS medium to form more than 2-3 mm yellow colonies.
Presenting symptoms: ulcers, rotten gills; complete appearance, generalized redness, gastrointestinal emptiness, slight swelling of the liver and pancreas but normal color, head and chest nails are easy to peel off.
2. Vibrio parahaemolyticus:
Gram-negative bacteria, the most suitable temperature of 30-37 °C, tolerated pH range of 6-8.5, salt-loving bacteria 20 ‰-30 ‰ breed faster, below 5 ‰ stop growing, can use sucrose and lactose, in TCBS medium to form more than 2-3 mm of blue-green colonies.
Symptoms: the body color of the shrimp is white and turbid and reddish, most of the liver and pancreas are enlarged, the texture is soft, the color is pale white or yellowish, and the liver and pancreas of some diseased shrimp are obviously atrophied. During the onset of shrimp disease, they usually swim slowly on the surface of the pond or lie on the slope of the pond, lose their appetite, and have an empty stomach.
3. Non-01 group Vibrio cholerae:
Gram-negative bacteria, which can tolerate pH values of 6-8.5, can grow and multiply in fresh water and high salinity, and can use monosaccharides or oligosaccharides to form yellow colonies of more than 2-3 mm in TCBS medium.
Symptoms: sluggish movement, sometimes floating head or tumbling on the surface of the water; swelling of the eyeball, from black to dark to ulcerated only the stalk of the eye, as the disease worsens the whole body muscles whitish, generally within a week of death.
4. Vibrio Harvey's:
Gram-negative bacteria, the most suitable temperature of 37 °C, can tolerate pH range of 5-9.5 salinity range of 20 ‰-30 ‰, 0% of fresh water does not grow, can use monosaccharides or oligosaccharides, in TCBS medium to form more than 1-2 mm yellow colonies.
Symptoms: in the early stage of the disease, the shrimp activity ability decreases, sinks to the bottom, mostly tumbles with the current of water, does not feed or eat less, does not emit light in the early stage of the disease, and will fluoresce when dying or after death.
Causes of Vibrio shrimp
In fact, there are very few pathogenic Vibrio, and the vast majority of Vibrio are beneficial bacteria. Fewer Vibrio bacteria cause disease in aquatic organisms. Vibrio is a conditional pathogenic bacterium. Vibrio has always been present in natural water bodies, and under normal circumstances, even healthy shrimp bodies may carry Vibrio, but they will not develop disease. Only under certain conditions will shrimp show obvious symptoms and even outbreaks.
1. The water quality is unstable, deteriorating and deteriorating.
The quality of the water in the pond directly affects the survival of the shrimp, and under the condition of excellent water quality, the shrimp is not prone to vibriosis.
2. Temperature is a factor that must be paid attention to in the growth of shrimp.
Shrimp growth has the most suitable temperature for growth, maximum temperature, minimum temperature, and the same Vibrio pathogenesis is also closely related to temperature. Studies have shown that at water temperatures of 24 to 30 °C, the number of shrimp dying from Harvey's vibrio disease increases due to the increase in temperature. At temperatures greater than 32°C or below 28°C, the growth rate of Vibrio Harvey's will slow down, and the mortality rate of shrimp dying from Vibrio disease will decrease. Temperature not only affects vibrio's ability to "adhere" to shrimp, but also affects its ability to produce toxins, which shows how important temperature is in the shrimp farming process.
3. Salinity.
Salinity is an important indicator that must be paid attention to in the growth of Penaeus vannamei, and as shrimp farming continues to develop inland, freshwater shrimp farming is no longer a new thing. However, shrimp farmers in freshwater shrimp farming or areas with high salinity need to pay attention to the salinity, and salinity can also become an important condition for the growth of Vibrio. Once the salinity changes too quickly, bringing stress to shrimp, the pathogenicity of Vibrio is also enhanced.
Therefore, in the process of desalining shrimp fry or in the process of breeding, it is not advisable to let the salinity of the pond change too quickly.
4. The pH value changes too much.
Shrimp farmers know that every pond is photosynthetic every day due to algae, the pH value in the morning and evening is not the same, and the best change floats within 1 as the normal value. If the pH value changes too much in the morning and evening, it will cause stress to the shrimp, and the pathogenicity of the arc rate will also be enhanced.
5. Decreased physique.
The decline in the physique of shrimp and the mutation of the external environment are the main reasons for the death of shrimp due to Vibrio. When the physique of shrimp declines, then the Vibrio bacteria in the water body and the shrimp body will multiply rapidly, which will induce various shrimp diseases and cause death.
Prevention and control of vibriosis of shrimp
1. Drug prevention and treatment
Western medicine: At present, the main treatment of gram-negative bacteria of broad-spectrum drugs such as "Nolikang", "blood stop", etc., these drugs have a strong inhibitory effect on Vibrio, but it is easy to produce resistance, while these drugs themselves will increase the load of the digestive system of farmed organisms, easy to cause shrimp feeding slowdown, liver and intestine disease.
Plant extracts: Plant extracts belong to natural medicines, with bacteriostatic and bactericidal effects, and no drug resistance, while also improving the body's immunity, improving disease resistance, in recent years by aquatic farmers respected. It was found that Vibrio algae, Vibrio hash, Vibrio parahaemolyticus, and Vibrio fluvices have sensitivity to "Eucalyptus essential oil" and "Huanglian extract", and at the same time have good bacteriostatic and bactericidal effects on four pathogenic Vibrio such as Vibrio eel, Vibrio parahaemolyticus, Vibrio estuaria and Vibrio cholerae.
2. Immune prevention and treatment
The use of immunostimulants, such as "bile acids" and "multi-dimensional", has the effect of activating the phenol oxidase system, while the combination of bile acids and multi-dimensional, effectively protects the shrimp liver and pancreas, and promotes the development of the liver and pancreas. Improves the phagocytosis of blood cells and the ability to digest and kill invading foreign microorganisms, thereby improving the immunity of shrimp.
3. Add fresh water in time to gradually reduce salinity
The current outbreak of Vibrio parahaemolyticus is Seawater Vibrio, also known as salt-loving bacteria, and the lower the salinity, the slower its growth and reproduction rate. In the past two years, many freshwater pond shrimp cultures have a high success rate, which fully explains the biological characteristics of Vibrio parahaemolyticus. Therefore, after the release of seedlings, conditional shrimp ponds can gradually add clean fresh water and reduce the salinity of pond water to inhibit the growth and reproduction of Vibrio parahaemolyticus, so as to achieve the purpose of preventing and controlling shrimp early death syndrome.
4. Irregular application of microbial preparations
Microbial agents have unique advantages for vibrio pathogenic bacteria in water and water quality control. Photosynthetic bacteria, EM bacteria, bacillus, nitrifying bacteria, etc. are used together to have a beneficial impact on farmed organisms in terms of changing the population structure of water and sedimentary microorganisms, eliminating or reducing the number of pathogenic microorganisms, and improving water quality.
The article comes from the frontier of shrimp farming!