Causes and prevention of bleeding symptoms in conventional fish

In recent years, with the increase of aquaculture density and the deterioration of water environment, there are more bleeding symptoms of conventional farmed fish, which has caused great losses to farmers. There are many causes of bleeding in fish, some are caused by viruses, some are caused by bacteria, and some are caused by feed and environmental stress. Farmers can not correctly diagnose the difference, often resulting in incorrect medicine, poor efficacy, and even a large number of dead fish serious consequences. The etiology, prevention and treatment of fish bleeding are as follows:

1. Viral hemorrhagic disease

1.1 pathogen

Caused by respiratory arc virus, the individual of the virus is very small and granular and can only be seen under an electron microscope.

1.2 main points of diagnosis

1.2.1 Ctenopharyngodon idellus, herring and wheat ear fish

1.2.2 the epidemic conditions are mainly prevalent in the provinces and cities of the Yangtze River Basin and the Pearl River Basin, especially in the middle and lower reaches of the Yangtze River, and also in North China in recent years. It is mainly prevalent in July and September every year, and the second peak at the turn of summer and autumn is the disease. The water temperature is 20 ℃ 33 ℃, and the most suitable popular water temperature is 27 ℃, but when the water quality deteriorates, the water temperature changes greatly, the fish body resistance is low, and the number of viruses is high and virulent, the disease also occurs when the water temperature is as low as 12 ℃ and as high as 34. 5 ℃. Grass carp and green carp, which are mainly harmful to fish in that year, can also be infected, and sometimes large grass carps over 2 years old also get sick. According to the speed of disease development, grass carp hemorrhagic disease can be divided into acute type and chronic type. The acute type developed rapidly, came fiercely, and died seriously. a large number of deaths occurred within 5 days after the onset, mostly in high-density grass carp intensive culture and monoculture ponds; the chronic type began to ease, with a small number of dead fish per day, and the peak of death was not obvious, but the course of the disease was longer, mostly in large-size fish ponds and adult ponds in August.

1.2.3 the symptoms of the disease are complex, and a series of symptoms can occur both in vivo and in vitro. The most basic symptoms are congestion and bleeding of related organs or tissues. In terms of physical symptoms, the body color of diseased fish is generally dark black or reddish. Small fish species in the sun or light perspective, you can see subcutaneous muscle congestion, bleeding; diseased fish's mouth, upper and lower jaw, top of the head, around the orbit, Gill cover, Gill and fin base hyperemia, sometimes exophthalmos; peel off the fish's skin, it can be seen that the muscle is punctate or massive hyperemia, bleeding, when the whole body muscle is bright red, when the Gill often shows "white Gill"; there are also Gill patches of scarlet hyperemia. From the perspective of internal lesions, the most common intestinal congestion, the whole intestine or part of the intestinal wall is bright red because of congestion, mild can show blood spots and intestinal wall ring bleeding. But the intestinal wall is still tenacious, there is no food in the intestine, the mesentery, the surrounding fat, swim bladder, gallbladder, liver, spleen and kidney also have bleeding spots or are covered with blood filaments. In some cases, the swim bladder and gallbladder are purplish red. When the muscle bleeding is serious, the color of liver, spleen and kidney often becomes pale and gray, or there may be local bleeding.

In fact, not all of these symptoms occur at the same time. According to the difference of symptoms and pathological changes, it can be divided into three types, which can occur at the same time or alternately. ① red muscle type: the main symptoms are obvious muscle bleeding, the whole body muscle is bright red, and the Gill filaments are pale due to severe bleeding, which are more common in 5-10cm grass carp species; ② red fin red Gill cover type: the main symptoms are severe bleeding in the fin base and operculum, with bleeding spots at the top of the head, mouth and orbit, mostly in large grass carp species above 10cm. ③ enteritis type: the main symptoms are severe intestinal congestion, all or part of the intestinal tract is bright red, visceral punctate bleeding, bleeding spots can also be seen on the body surface, can be seen in various specifications of grass carp.

1.3 main points of prevention and control

1.3.1 prevent the thorough disinfection of the pond; the fish in the lower pond should be bathed with 50-60ml/m3 "strong iodine" (mainly povidone iodine) for 20-30 minutes and conditionally injected with inactivated vaccine against hemorrhagic disease, which is the most effective way; adhere to the "four determinations" and strengthen the management of water quality. In addition, the production practice shows that the occurrence of grass carp hemorrhagic disease is related to stocking density and stocking mode. The incidence of grass carp hemorrhagic disease in sparse culture ponds is lower than that in dense ponds, and that in mixed ponds is lower than that in monoculture ponds. Therefore, the implementation of sparse culture and mixed culture can reduce the harm degree of the disease.

1.3.2 treatment

The virus is parasitic in fish tissues and cells and has strong drug resistance, so it is difficult to treat with drugs. The use of drugs has a certain effect in the early stage of the disease, and the use of external and internal drugs at the same time can enhance the curative effect. ① drugs for external use were sprinkled with "potent iodine", "Sanmu Ling" or strong chlorine in the whole pool, once every other day, twice continuously; ② was given orally, adding 4-6 grams of virus powder, 0.5-1 grams of enrofloxacin, 4 grams of VC2-4 grams and VE 1 grams per kilogram of feed for 6-7 days.

2. Fulminant hemorrhagic disease (bacterial septicemia)

2.1 pathogen

Aeromonas hydrophila, Aeromonas aeruginosa, Yersinia Luke and other bacteria.

2.2 main points of diagnosis

2.2.1 the specificity of pathogen to host is not strong, silver carp, bighead carp, crucian carp, carp, grass carp, common carp, mandarin and other conventional farmed species will be infected and pathological changes will occur.

2.2.2 the epidemic season of the disease is long. From the end of February to November, the water temperature is between 9-36 ℃, especially when the water temperature is above 28 ℃ and the water temperature is still above 25 ℃ after the high temperature season. If it suddenly clears up after a continuous rainy day, the temperature rises sharply and the water environment worsens, the disease is more likely to break out.

2.2.3 in the early stage of the disease, from the appearance observation, the mouth, abdomen, operculum, orbit, fin and both sides of the fish showed mild hyperemia. When the abdominal cavity was opened, a small amount of food was still found in the intestines. With the development of the disease, the above-mentioned body surface congestion intensified, muscles showed bleeding symptoms, orbital congestion, exophthalmos, abdominal swelling, redness and swelling. Abdominal incision is obvious, due to damage to internal organs (liver, spleen, kidney, etc.), resulting in accumulation of yellow or red ascites in the abdominal cavity, enlargement of liver, spleen and kidney, intestinal wall congestion, inflation and lack of food. Gill gray shows anemia, sometimes purple and swollen, and in severe cases, the ends of the Gill filaments rot. From March to April, the symptoms of inflammation and congestion on the body surface of diseased fish are as follows: head, mouth, operculum, orbit and both sides of body surface, especially under ventral fin and caudal stalk. Exophthalmos, Gill anemia, internal organs with varying degrees of inflammation can be seen in some diseased fish, and sometimes inflatable swelling can be seen in the intestines. The symptom of diseased fish after 5 months is that the body surface is inflamed by congestion of the lower margin of the operculum, fin base and viscera, and sometimes the mouth and muscles are also inflamed at the same time. At this stage, the clinical symptoms of diseased fish are more complex, sometimes the physical symptoms are not obvious, the fish die, and the symptoms of each diseased fish are not exactly the same, so it is difficult to have an absolute boundary.

2.3 points of prevention and control

2.3.1 prevent ① from dredging excessive silt and thoroughly clear the pond for disinfection; ② regularly inject water and disinfect the water to keep the water quality fresh and kill pathogens; ③ strictly controls the feed quality to improve the disease resistance of fish; ④ carries out regular drug prophylaxis, taking some drugs to treat hemorrhagic disease every 20 days or so, such as Yuxue Kangning, Fukang, Sihuang detoxification powder, etc. ⑤ regularly disinfects water with "Sanmuling", "Xueting" or quaternary ammonium salts; when ⑥ finds parasitic diseases, enteritis, rotten gills and body surface injuries, it should be treated in time to avoid secondary infection.

2.3.2 treatment is divided into four steps. On the first day of ①, to kill body surface parasites, commercial fishing drugs such as "Chong Lijing", "double killing order" and "killing fish and insect pests" can be sprinkled in the whole pool according to the instruction; on the second day of ②, kill pathogenic bacteria both in vivo and in vitro, sprinkle in the whole pool with strong chlorine, and the pool water is 0.3~0.4ppm, once every 3 days. Can also be used "anti-violence" and other insecticidal and germicidal drugs can be completed at one time; ③ internal administration, each kilogram of feed added "Yuxue Kangning" 3-4 grams for 6 days, while adding VC2-4 grams, VE1g adjuvant treatment, the effect is more obvious. If the condition is serious, enrofloxacin 0.5g can be added; ④ adjusts the water quality, after recovering from the disease, after replacing part of the pool water, use quicklime 1 meter deep 10~15kg per mu, sprinkle the whole pool once after dissolving water to regulate the water quality and eliminate drug residues at the same time.

3. Nutritional hemorrhagic disease

3.1 etiology

3.1.1 Vitamin deficiency

It is proved by experiments that insufficient addition of vitamins in feed, or production process problems, or improper storage of feed and other reasons lead to insufficient vitamins in feed, which will cause fish bleeding. When the fish body lacks vitamin C, the vascular permeability increases, and the end of the blood vessel is slightly in the stress state, resulting in non-destructive skin bleeding; vitamin K deficiency will prolong the clotting time of the blood. In addition, fish lack of vitamin E, vitamin B2 and so on may also show bleeding symptoms.

3.1.2 addition of olaquindox and flavomycin

As an antibacterial and growth-promoting drug, olaquindox has obvious growth-promoting effect and can play a role similar to hormone. If it is used in large quantities or for a long time, it will produce strong side effects, such as poor anti-stress ability, easy injury and bleeding of fish, intolerance to pulling nets, high transportation mortality and decreased disease resistance. Moreover, quinolinol has cumulative toxicity, and the side effects of quinolinol can not be seen until the adult stage when the young fish are fed with the feed containing quinolinol. The state has banned the addition of olaquindox to aquatic feed. Although the Ministry of Agriculture allows the addition of an appropriate amount of flavomycin to feed, there will also be a decline in anti-stress ability, especially in combination with olaquindox, its toxicity will be enhanced.

3.2 Prevention and control measures

① to buy high-quality feed produced by regular feed manufacturers, generally regular large factories will not have vitamin deficiency and the addition of prohibited drugs, small factories due to poor management of additives or production technology and other reasons, resulting in vitamin deficiency; ② feed requires comprehensive nutrition, reliable quality, adding multivitamins in the feed every 15 days for 4-5 days.

4 stress hemorrhagic disease

4.1 etiology

In summer, when the water temperature is high and the water quality is poor, the fish do strenuous exercise because of the shock, the endocrine is strengthened and the oxygen consumption increases, while the water quality worsens and the dissolved oxygen in the water is seriously insufficient and there is a strong stress reaction. It is mainly caused by hypoxia, bacterial toxins and other factors that cause the dysfunction of nervous system regulation, the increase of capillary permeability and the leakage of blood vessels through the wall of red blood cells. Megalobrama amblycephala has poor resistance and strong activity, so it is more prone to stress reaction.

4.2 Prevention and control measures

① generally strengthens the water quality regulation before pulling the net, carries on the water body disinfection, adds the amount to feed the vitamin C, and so on, can be well prevented; ② in the feed compatibility every ton of formula feed adds fish anti-stress drugs; ③ culture process, pay attention to the regulation of water quality, through various ways to improve the immunity of fish.