With the highly intensive development of aquaculture, farmed fish are facing more and more stress factors, especially in recent years, a fish with bleeding as the main symptom has occurred in aquaculture (silver carp most Obvious) stress disease, which brings serious economic losses to production.
The disease is mainly manifested as: when the farmed fish are stimulated by stress factors (such as pulling net fishing, weather changes and long-distance transportation, etc.), they can suddenly and quickly occur systemic surface and gill hemorrhage and die in large numbers.
The etiology of fish stress hemorrhage is complex, and the prevention and treatment is difficult. The disease is a non-infectious disease after pathological research and analysis.
Human factors: intensive farming, fishing, transfer, transportation, poor feed, etc.
Environmental factors: poor water quality, sudden changes in water temperature, sudden changes in climate, low pressure, etc.
Biological factors: bacteria, germs and parasites, etc.
2. Onset characteristics
(1) The incidence is not seasonal and can occur throughout the year. The peak period of incidence is from July to October, and the incidence is the most serious in the midsummer heat; the water temperature is more than 25 ℃, the most serious incidence is 28-32 ℃, and it rarely occurs below 20 ℃; the fish with stress bleeding will gradually decrease in the water temperature. Symptoms will gradually decrease or even disappear.
(2), all kinds of farmed fish can occur. However, silver carp and carp are the most prominent, followed by grass carp, crucian carp, bream, and silver carp. It can occur from fingerling to adult stage, but the incidence of adult fish is generally high.
(3) The disease mostly occurs in aquaculture which is mainly fed with feeds with high nutritional content such as protein and energy. And the disease occurs under the stimulation of stress factors, such as fishing and long-distance transportation when fish are divided into ponds, transferred to ponds, transferred to boxes, and sold.
(4) The disease is more common in high-density culture ponds and cages. However, it rarely occurs under the breeding conditions of thinner density, lower feed quality and higher crude fiber content. Especially after overfeeding the feed supplemented with olaquindox (growth hormone), the incidence rate will increase, and the disease will be more serious.
(5) In fish ponds in the same area or cages in the same water body, if fed several feeds produced by different manufacturers, or fed feeds from the same manufacturer, only some fish get sick, while others do not.
(6) The diseased fish generally grow faster than the unaffected fish. Even in the same infected fish pond or cage, fast-growing and fat fish were severely ill, while individual thin fish were less ill or even not ill.
(7) The use of antibiotics to treat diseased fish is ineffective or very ineffective. The use of vitamin C, E, etc. has a certain effect, but it is not ideal.
(8), sudden onset. There is no abnormality in the fish before the onset of the disease, but when the fish is stimulated by stress factors, symptoms often appear within a few minutes, ten minutes or dozens of minutes, and die soon, showing the anti-stress ability of the fish Very poor.
Before the onset of the disease, the fish had no obvious symptoms and had normal activities, but when they were stimulated by stress factors such as fishing and pulling nets, poor water quality, sudden changes in water temperature, and long-distance transportation, the fish showed very sensitive, extremely restless, and violent beating. Sudden, rapid occurrence of hyperemia and hemorrhage of the entire body surface and mass death.
Sometimes when exposed to stress factors, the abdomen, head, mouth corners, gill covers, gill filaments, and bases of fin rays are significantly congested, red, and bleeding within tens of seconds to a few minutes. Blood gushed from under the gill covers and stained the water.
Sick fish are particularly intolerant of long-distance transportation, and most of them die during transportation. Even if they are not dead, they are in critical condition.
The secretion of mucus on the body surface of the diseased fish decreases, and the hand feels rough; the muscle water increases, and the body surface feels swollen; the anus is slightly red and swollen, and the intestine is slightly congested; the liver is enlarged and the texture becomes brittle; the gallbladder is dilated, and the bile is full; Congestion was enlarged and was purple-black; the heart was slightly enlarged and the color became pale; the amount of pale ascites accumulated in the abdominal cavity.
4. Prevention and control measures
1. The formula of compound feed should be nutritionally balanced. Attention should be paid to nutritional balance when designing feed formulations, and energy and crude protein standards must be considered to keep them at a reasonable level. Feed different ratios of feeds in different growth periods of fish, especially the protein content should be just right and the proportion should be appropriate. Growth hormones that do not use olaquindox.
2. Appropriately match and feed natural bait or other feed. Such as grass carp feeding grass, herring, carp feeding snail and so on.
3. Do not abuse stimulant drugs. It is advisable to use drugs with low irritation, good effect and wide adaptability, such as chlorine dioxide, dibromohydantoin, bromochlorohydantoin, Chinese herbal medicine preparations, and biological preparations to avoid long-term stimulation of the fish body, resulting in poor stress ability .
4. Try to avoid fishing and transportation during high temperature periods (periods). When fishing and transporting, the action should be slow and light, and soft nets and means of transport should be used.
5. When the weather changes suddenly, do a good job in the water quality adjustment and oxygenation and cooling arrangements of the fish pond, so as to achieve early prediction and early prevention.
6. The stocking density should not be too large. The ecological breeding method is adopted to improve the environment for the survival and growth of fish and improve the anti-stress ability of fish.
7. Strengthen the feeding management, improve the water quality, and keep the water quality fresh. It is reported that regularly splashing the whole tank with quicklime slurry can not only improve the water quality, but also enhance the ability of the fish to resist stress.
8. If you want to carry out work such as binning, pond transfer, fishing and transportation in the near future, you should feed anti-stress drugs for a period of time in advance, such as adding darline, pantothenic acid, niacin, sodium succinate fumarate, traditional Chinese medicine astragalus, thorn. Wujia, etc. to enhance the anti-stress ability of the fish.
9. After the onset of the disease, in addition to immediately improving and adapting to the living environment of the fish, apply anti-stress and hemorrhagic drugs.