Silver carp is a kind of fish culture, and it is in a subordinate position in the ponds where carp, crucian carp, grass carp and bream are mainly raised. The pond selection is completely consistent with the main fish culture types applied for certification above.
Water quality requirements
The water quality requirements of silver carp are completely consistent with those of the main carp that has applied for certification.
Seedling requirements
Before stocking, fry must go through inspection and quarantine, and select the ones with pure quality, health and good specifications. The stocking time is in the middle and late May. 1. Fish feeding
Fish fry stocking: In the middle and late May, when the water temperature in the pond is stable above 18℃, it is the suitable time for stocking. Put silver carp and mullet at a density of 3-5 strips per square meter. Feeding management: After the fry enter the pond, they mainly feed on zooplankton and crumbs.
Adult fish culture: specification and density of fish species. The specification of overwintering fish species is100-200g/fish, and the stocking density is 0.4-0.5 fish/㎡.
Silver carp is a kind of fish culture, which is based on the time when carp leave the pond.
2. Overwintering management
Overwintering density: The overwintering density of adult fish and fingerlings in pressure tanks is generally 0.3-0.6㎏/㎡. Can be adjusted according to the situation of the pond.
Requirements for overwintering fish: the fish should be free from disease and injury, fat and strong.
Overwintering method: The overwintering pool should be relatively clean, with good water retention, and the water depth under ice should be kept at about 1.5m, and ponds should be merged according to different specifications: before freezing, the whole pool should be sprayed with 90% crystal trichlorfon 1.5-3.0kg/ ha, and the phytoplankton quantity should be kept at 25-50 mg/L. In order to keep the water surface transparent, it should be timely.
2. Fish fry and fingerlings enter Tang Qian and are soaked in 2.0% saline for 5- 10 minute for disinfection;
3. In high temperature season, the food market is disinfected by hanging bags with bleaching powder or a mixture of copper sulfate and ferrous sulfate every month.
4. Regularly use microbial agents to adjust water quality and improve fish immunity; 5. The dead fish should be fished out in time and buried deeply.
6. Fish disease treatment.
Common diseases
Pathogenic gill mold
Symptoms: the sick fish does not eat, swims slowly, the gills are congested and bleeding, and the gills are a little congested, losing their normal bright red and turning pink or pale. In severe cases, gill filament necrosis affects respiratory function and leads to the death of sick fish.
Prevention and control methods:
1. Thoroughly clean and disinfect the pond, keep the water quality clean and prevent the water quality from deteriorating.
2. The culture water quality requires the application of fermented and decomposed organic fertilizer, which is not suitable for raw application. 3. The sick pond should be quickly filled with clean water to improve the water quality, or the sick fish should be transferred to a pond with fresh and clean water quality.
Spraying 4.20-30 mg/L quicklime in the whole pond can reduce the organic matter content in the water and improve the water quality.
Spotted subspecies
Pathogens: Aeromonas hydrophila and aeromonas sobria.
Symptoms: A round erythema appeared on the back of the dorsal fin of the diseased fish, and the scales at the focus fell off, eventually forming an ulcer or even exposing bones or internal organs.
Prevention and control methods:
1. Because the excrement of herbivores (such as cattle and sheep) is the breeding ground of single bacteria, when applying quicklime in fish ponds, it must be mixed and fully fermented, and it can only be used after rotting to prevent pathogens from entering.
2. Fish can be soaked in 2% salt solution for 5- 10 minutes when crossing the pond, which can effectively prevent the disease.
3. Use disinfectant for external use when you are sick. External disinfection: 0.5ppm of bacterial toxin or 0.3ppm of dibromohydantoin overflowed from the whole pool.
Dactylogyriasis
Pathogen: Dactylogyrus
Symptoms: When the disease is serious, the gill filaments of the diseased fish swell, mucus increases, and breathing is difficult, which can lead to a large number of fry deaths.
Prevention and control methods:
1.90% crystal trichlorfon 0.3-0.7ppm overflowed from the whole pool.
2. Sweep insects in the whole pool according to 130ml- 170ml/ mu/m, and use it again every other day when the condition is serious.
Diphtheria of silver carp
Diptera belongs to Diptera, Schizocephalidae. The first intermediate host is copepods, the second intermediate host is fish, and the last host is fish-eating birds. In the past, there were occasional crucian carp and wild miscellaneous fish in some large and medium-sized reservoirs, and they were often concentrated and infected, and there was a spreading trend. It mainly causes great harm to the first-year-old silver carp species, and the highest infection rate in the pond can reach 92%. When the infection intensity is the highest, there are 13 sparganoids in the body cavity of each silver carp. The highest mortality rate of sick fish in winter is 84%. However, the infection situation varies from year to year, which is mainly related to the change of water environment (the decrease of water area caused by drought) and the activities of waterfowl. This paper analyzes the causes of the disease and puts forward the prevention and control countermeasures.
First of all, the symptoms of sick fish
From the outside, the abdomen of the diseased silver carp is swollen and swollen locally. After thawing in early spring, its physique was obviously emaciated, its abdomen expanded more obviously, and its abdominal muscles were extremely thin. Squeeze the abdomen hard, and the sparganum can be drilled from the pectoral fin. Most sick fish died during transportation, and only a few survived. The susceptible host of Diptera is mainly silver carp, and the main infection of carp is the coelacanth.
Second, the etiology analysis
1. Ponds near reservoirs and swamps, or ponds with open water surface, secluded environment and few people, often have many waterfowl such as herons, red-billed gulls and kingfishers inhabiting here from spring to autumn and swimming between reservoirs and fish ponds. The infection rate of sparganum mostly occurs in large wintering ponds. Every spring, when the ice surface of these ponds melts, sick or weak fish often swim on the water surface, attracting a large number of waterfowl to prey, and feces with eggs are discharged into the water, causing infection.
2. Some ponds sell out spring seedlings, and then water is injected to raise spilled seedlings, because time is tight and there is no time to clean the pond. Some ponds (shallow ponds with water) are frozen thoroughly in winter, thinking that they can clear the ponds, and summer flowers and fry will be released soon after water injection. Adults, the first intermediate host of Diptera (copepods), can overwinter as eggs, and the number of dormant bodies can reach hundreds to millions per square meter, which is often highly concentrated in a small area. It is precisely because copepods have this adult dormancy adaptability that a considerable number of mature copepods with eggs will appear soon after fresh water is injected into fish ponds without medical cleaning. In early spring, the ice and snow just melted, and a large number of copepods with eggs were seen in some shallow water pits in winter, which also shows that copepods can resist the harsh environment. To sum up, in some ponds, a large number of copepods are hidden in the water because the ponds are not cleaned with drugs, which has laid a hidden danger for the infection of Diptera.
3. According to the biological characteristics of fry, the feeding habits of splash fry will change from rotifer to larger zooplankton when they enter summer flowering period. Some fish farmers consciously cultivate some cladocera and copepods for the summer flower fry in the lower pond. However, if there is no artificial control, copepods are likely to become the dominant population. Because copepods are specific for swallowing hookworm, if there are water birds with pathogens near the pond, summer flower fry are very susceptible to Diptera infection. 4. Some fish farmers buy summer flower fry infected with sparganum from areas with high incidence of Diptera. Even if there is no condition for taeniasis in the local area, the fry have swallowed the copepods infected with protocercaria, developed into sparganum in the fish body cavity, and excreted at the same time, resulting in a large number of Diptera infections in the fry pond.
Third, prevention and control countermeasures
First of all, we should raise the fry well. If the fry are shipped from other places, we should first investigate whether the fry supplier has a history of tapeworm. If summer flower fry are raised by ourselves, there is a history of tapeworms in the local area, or there are waterfowl activities, then the first intermediate host and copepods should be killed before the splashed fry enter the pond. Copepods in the pond should also be removed. In addition, it is necessary to enhance the awareness of bird protection, study effective methods that do not harm the life of the ultimate host, and drive away waterfowl. In areas with frequent taeniasis, we must insist on cleaning ponds with quicklime.
Commonly used drugs
Jia Chongqing
Main ingredients and content: rhubarb
Description: yellow-brown powder, fragrant smell.
Function and use: sterilization and insecticidal. It is mainly used for ciliates such as rotifers and oblique tube worms.
Usage and dosage: sprinkle it on the whole pond at the ratio of100-200g/mu/m, and use it 1-2 times.
Withdrawal period: 30 days
Insect cleaning
Main composition and content: 2.5% dithiocyanomethyl alkane.
Description: Brown liquid.
Function and use: sterilization and insecticidal. Mainly used for fish parasites such as ciliates and worms.
Usage and dosage: At onset, add 130ml- 170ml/ mu/m water and sprinkle it all over the pool. You can use it every other day when the condition is serious.
Note: Do not use other pesticides or fungicides for four days before and after use.
Withdrawal period: 30 days bacterial toxin.
Main composition and content: sodium chlorite, 80%.
Properties: white powder or granules.
Function and use: sterilization and insecticidal. Mainly used for hemorrhagic disease, gill rot, enteritis, vertical scale disease, water mold and so on.
Usage and dosage: Spray 0.37-0.5ppm water on the whole pool when the disease occurs. You can use it every other day when the condition is serious.
Precautions: A and B are mixed in the open air and are ready to use.
Withdrawal period: 10 days.
Bromine-rich hydantoin
Main ingredients and content: dibromohydantoin, 30%.
Description: White powder
Function and use: sterilizer. Mainly used for hemorrhagic disease, gill rot, enteritis, vertical scale disease, water mold and so on.
Usage and dosage: spray 0.3ppm water on the whole pool at onset. When the condition is serious, double use or continuous use for 2 days.
Withdrawal period: before fishing 10 day.
Yi Shui Sheng su
Main components and contents: Bacillus, photosynthetic bacteria, nitrifying bacteria, nitrogen-fixing bacteria, etc. Number of viable bacteria >; 70 billion/gram.
Description: taupe powder
Functions and uses: Water quality improvement drugs. Remove organic pollutants, ammonia nitrogen, nitrite and other harmful substances in aquaculture water, increase dissolved oxygen in water and adjust PH value.
Usage and dosage: according to the deterioration of water quality, soak each mu with 200-300g of water 1 m, and then splash it all over the pool.
Precautions: Do not mix with disinfectants or pesticides when using; Disinfectant shall not be used within 3 days before and after application. Soak in water for 1-2 hours.