Characteristics and preventive measures of stress hemorrhagic disease in fish

With the highly intensive development of aquaculture, farmed fish are faced with more and more stress factors, especially in recent years, a fish stress disease with bleeding as the main symptom has occurred in aquaculture, which brings serious economic losses to production. The main manifestation of the disease is that when cultured fish are stimulated by stress factors (such as net fishing, weather mutation and long-distance transportation, etc.), systemic surface and Gill bleeding can occur suddenly and quickly, resulting in mass death.

The etiology of fish stress hemorrhagic disease is complicated and it is difficult to prevent and cure. According to pathological analysis, the disease is a kind of non-communicable disease.

I. characteristics of the disease

The main results are as follows: 1. the disease is not seasonal and can occur all the year round. The peak period of the disease is from July to October, and the most serious is the heat in midsummer, the most serious when the water temperature is above 25 ℃, the most serious when the water temperature is 28-32 ℃, and rarely below 20 ℃. When the water temperature decreases gradually, the symptoms of the fish with stress bleeding will gradually alleviate or even disappear.

2. All kinds of farmed fish can occur, but carp is the most prominent, followed by grass carp, crucian carp, carp 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 the culture where the feed with high nutrient content such as protein and energy is fed, and the disease occurs under the stimulation of stress factors, such as fish pond division, pond rotation, box transfer, fishing and long-distance transportation during sale.

4. The disease is most common in high-density ponds and cages, but rarely occurs under the culture conditions of sparse density, low feed quality and high crude fiber content. Especially after excessive feeding with olaquindox, the incidence increased, and the disease will be more serious.

5. When fish ponds in the same area or cages in the same body of water are fed with several kinds of feed produced by different manufacturers, or fed with feed from the same factory, only some fish get sick, while others do not.

6. diseased fish generally grow faster than those without disease. even in the same diseased fish pond or cage, the fast-growing and hypertrophic fish are seriously ill, while the thin fish have less or no disease.

7. the treatment of diseased fish with antibiotics is ineffective or ineffective, and the use of vitamins C and E has a certain curative effect, but it is not ideal.

8. The attack is sudden. There is no abnormal phenomenon in the fish body before the onset of the disease, but when the fish are stimulated by stress factors, they often appear symptoms within a few minutes, ten minutes or dozens of minutes, and die quickly, showing that the anti-stress ability of fish is very poor.

Second, main symptoms

In most cases, the fish body is not obviously abnormal, but once the fish is dragged, fished and transported, the fish body is very sensitive, extremely restless, and beating violently. Within tens of seconds to a few minutes, the abdomen, head, corner of mouth, Gill cover, Gill filament, and the base of the fin are significantly congested and red. In severe cases, the Gill filament bleeds seriously, and a large amount of blood gushes out from under the Gill cover and dye the red water body. Diseased fish are particularly intolerant of long-distance transportation, and most of them die in the course of transportation. even if they do not die, they are in critical condition, turn pink all over the body, become hard, and eventually die or lose their commodity value.

Diseased fish body surface mucus secretion decreased, hands feel rough; muscle moisture increased, body surface edema; anus mild redness, intestinal congestion; liver swelling, brittle texture; gallbladder dilatation, bile filling; splenic congestion, purple-black; heart slightly enlarged, color lighter; how many yellowish ascites accumulated in the abdominal cavity.

III. Preventive measures

1. The formula of formula feed should be nutritionally balanced. Different proportions of feed should be fed in different growth periods of fish, especially the protein content should be just right and the proportion should be appropriate. Control the use of quinolinol growth hormone (50g / ton feed).

2. Properly match and feed natural bait, such as forage, snail, etc.

3. Do not abuse drugs with strong irritation, but should choose drugs with small irritation, good effect and wide range of adaptation, such as chlorine dioxide, dibromohydantoin, bromochlorohydantoin, Chinese herbal medicine and biological agents, so as to avoid long-term stimulation of fish, resulting in poor stress ability.

4. Avoid fishing and transportation in high temperature period. Fishing and transportation 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 regulation of water quality and the arrangement of increasing oxygen and cooling in fish ponds, so as to make early prediction and early prevention.

6. The stocking density should not be too high. Ecological culture should be adopted to improve the survival and growth environment of fish and improve the anti-stress ability of fish.