Causes and Prevention Methods of Common Fish Hemorrhage Symptoms

In recent years, with the increase in aquaculture density and the deterioration of water environments, the phenomenon of hemorrhage symptoms in commonly farmed fish has become more frequent, causing significant losses to farmers. There are many causes of hemorrhage symptoms in fish; some are caused by viral infections, some by bacteria, and others by feed and environmental stress factors. Because farmers cannot correctly diagnose and distinguish the causes, they often end up using the wrong medication, achieving poor results, and even causing serious consequences such as mass fish deaths. The following are several causes of fish hemorrhage and their prevention and treatment methods:

1. Viral Hemorrhagic Disease

1.1 Pathogen

Caused by respiratory arc virus; the virus particles are extremely small, granular in shape, and can only be seen under an electron microscope.

1.2 Diagnostic Key Points

1.2.1 Affected species: grass carp, black carp, stone moroko

1.2.2 Outbreak conditions: mainly prevalent in the provinces and cities of the Yangtze River basin and Pearl River basin, especially in the middle and lower reaches of the Yangtze River; in recent years it has also occurred in North China; mainly prevalent from July to September each year, with the second peak of outbreaks at the turn of summer and autumn most often attributed to this disease; water temperature 20-33°C, with the optimal epidemic water temperature being 27-30°C, but when water quality deteriorates, water temperature changes greatly, fish body resistance is low, and the number and virulence of the virus are high, outbreaks can also occur at water temperatures as low as 12°C and as high as 34.5°C; mainly harms 5-20cm grass carp fingerlings and black carp fingerlings of the current year, stone moroko can also be infected, and sometimes large grass carp over 2 years old also contract the disease. According to the speed of disease progression, grass carp hemorrhagic disease is divided into acute and chronic types. The acute type has a sudden onset, is fierce, and causes severe mortality, with mass deaths occurring within 3-5 days after onset, mostly in high-density grass carp intensive and monoculture ponds; the chronic type has a relatively mild onset, with few fish dying daily, no obvious mortality peak, but a longer disease course, mostly occurring in August in sparsely stocked large-size fingerling ponds and adult fish ponds.

1.2.3 Symptoms: The symptoms of this disease are complex, with a series of symptoms appearing both internally and externally, the most basic being congestion and hemorrhage of the relevant organs or tissues. From external symptoms, the diseased fish body color is generally dark black or slightly red. In smaller fingerlings, when viewed against sunlight or lamplight, subcutaneous muscle congestion and hemorrhage can be seen; the diseased fish has congestion in the oral cavity, upper and lower jaws, top of the head, around the eye sockets, operculum, gills, and fin bases, sometimes with exophthalmos; after removing the fish skin, muscle congestion and hemorrhage in dot or block form can be seen, and in severe cases the whole body muscle appears bright red, at which point the gills often appear as "white gills"; there are also cases where gill lamellae show bright red patchy congestion. From internal lesions, the most common is intestinal congestion, with the whole intestine or part of the intestinal wall appearing bright red due to congestion; in mild cases, bleeding points and annular hemorrhage of the intestinal wall may appear. However, the intestinal wall still retains toughness, with no food in the intestine; the mesentery, surrounding fat, swim bladder, gallbladder, liver, spleen, and kidney also have bleeding points or are covered with blood streaks; in individual cases, the swim bladder and gallbladder appear purplish red; when muscle hemorrhage is severe, the color of the liver, spleen, and kidney often becomes pale, appearing grayish white, or with localized hemorrhage.

In fact, the above symptoms do not all appear simultaneously. According to differences in symptom manifestation and pathological changes, they can be roughly divided into three types, which may appear simultaneously or alternately. (1) Red muscle type: the main symptom is obvious muscle hemorrhage, with the whole body muscle appearing bright red, and gill filaments appearing pale due to severe hemorrhage, mostly seen in 5-10cm small grass carp fingerlings; (2) Red fin and red operculum type: the main symptom is severe hemorrhage at the fin bases and operculum, with bleeding points on the top of the head, oral cavity, eye sockets, etc., mostly seen in grass carp fingerlings over 10cm; (3) Enteritis type: the main symptom is severe intestinal congestion, with the entire intestine or part of it appearing bright red, dotted hemorrhage in internal organs, and bleeding points also visible on the body surface, seen in grass carp fingerlings of all sizes.

1.3 Prevention and Treatment Key Points

1.3.1 Prevention: Thorough disinfection of the pond; fingerlings introduced into the pond should be bathed in 50-60ml/m3 of "Strong Effect Iodine" (main ingredient: povidone-iodine) for 20-30 minutes; where conditions permit, injection of hemorrhagic disease inactivated vaccine is the most effective approach; adhere to the "four fixed" principles in feeding and strengthen water quality management. In addition, production practice shows that the occurrence of grass carp hemorrhagic disease is related to stocking density and stocking method; generally, sparsely stocked ponds have a lower incidence rate than densely stocked ponds, and polyculture ponds have a lower incidence rate than monoculture ponds. Therefore, implementing sparse stocking and polyculture can reduce the severity of this disease.

1.3.2 Treatment

This virus parasitizes in fish tissue cells and has strong drug resistance, so it is difficult to treat with medication. Medication in the early stage of the disease has a certain effect; simultaneous external application and oral medication can enhance efficacy. (1) External medication: dissolve "Strong Effect Iodine", "San Mu Ling" or strong chlorinated isocyanurate in water and splash over the entire pond, once every other day, for 2 consecutive applications; (2) Oral medication: add 4-6 grams of "Virus Powder", 0.5-1 gram of enrofloxacin, 2-4 grams of VC, and 1 gram of VE per kilogram of feed, administered continuously for 6-7 days.

2. Explosive Hemorrhagic Disease (Bacterial Septicemia)

2.1 Pathogen

Aeromonas hydrophila, Aeromonas sobria, Yersinia ruckeri and other bacteria.

2.2 Diagnostic Key Points

2.2.1 Affected species: The pathogen has low host specificity; silver carp, bighead carp, crucian carp, bream, grass carp, common carp, mandarin fish and other commonly farmed species can all be infected and develop lesions.

2.2.2 Outbreak conditions: This disease has a long epidemic season, from the end of February to November, with outbreaks occurring at water temperatures between 9-36°C, and is especially severe when water temperature remains above 28°C and when water temperature remains above 25°C after the high-temperature season. If after consecutive rainy days it suddenly clears up, temperature rises sharply, and the water environment deteriorates, outbreaks of this disease are even more likely.

2.2.3 Symptoms: In the early stage of the disease, from external observation, the diseased fish shows mild congestion symptoms in the oral cavity, abdomen, operculum, eye sockets, fins, and both sides of the body. Upon opening the abdominal cavity, a small amount of food is still visible in the intestine. As the disease progresses, the above body surface congestion intensifies, muscles show hemorrhagic symptoms, congestion around the eye sockets, exophthalmos, abdominal distension, redness and swelling. Upon opening the abdominal cavity, it is clearly visible that due to damage to internal organs (liver, spleen, kidney, etc.), yellow or red ascites accumulates in the abdominal cavity, the liver, spleen, and kidney are enlarged, the intestinal wall is congested and inflated with no food. The gills appear grayish white indicating anemia, sometimes purple and swollen, and in severe cases, the tips of gill filaments rot. In March-April, the body surface inflammation and congestion symptoms appearing in diseased fish are: head, mouth, operculum, eye sockets and other areas as well as both sides of the body surface, especially below the pelvic fins and at the caudal peduncle; some diseased fish show exophthalmos, gill anemia, and internal organs with varying degrees of inflammation, and sometimes intestinal inflation and swelling can also be seen. After May, the symptoms of diseased fish are mostly congestion and inflammation at the lower edge of the operculum, fin bases, and internal organs, and sometimes the oral cavity and muscles also show simultaneous congestion and inflammation. Because the clinical symptoms of diseased fish at this stage are relatively complex, sometimes the body signs are not obvious and the fish dies, and the symptoms of each diseased fish are not completely identical, it is difficult to draw an absolute boundary.

2.3 Prevention and Treatment Key Points

2.3.1 Prevention: (1) Remove excess sludge and thoroughly disinfect the pond; (2) Regularly add water and disinfect to maintain fresh water quality and kill pathogens; (3) Strictly control feed quality to improve the disease resistance of fish; (4) Regularly carry out medication prophylaxis, orally administering medications for hemorrhagic disease such as Yuxue Kangning, Fukang, Sihuang Jiedu Powder, etc., approximately every 20 days; (5) Regularly disinfect water bodies with "San Mu Ling", "Bao Xue Ting" or quaternary ammonium salts; (6) When parasitic diseases, enteritis, gill rot, or body surface injuries are found, treat promptly to avoid secondary infections.

2.3.2 Treatment is divided into four steps. (1) On the first day, kill external parasites on the body surface; choose commercial fishery drugs such as "Chong Li Jing", "Shuang Sha Ling", "Yu Chong Mie" and splash over the entire pond according to the dosage on the instructions; (2) On the second day, kill pathogenic bacteria inside and outside the body; splash strong chlorinated isocyanurate over the entire pond at a concentration of 0.3-0.4ppm, once every 3 days. Alternatively, use drugs such as "Kang Bao Wei" that both kill parasites and bacteria in one application; (3) Oral medication: add 3-4 grams of "Yuxue Kangning" per kilogram of feed, administered continuously for 6 days, while adding 2-4 grams of VC and 1 gram of VE as auxiliary treatment for more obvious results. For severe cases, add 0.5 grams of enrofloxacin; (4) Regulate water quality: after the disease is cured, replace part of the pond water, then use quicklime at 10-15kg per mu at 1m depth, dissolve in water and splash over the entire pond once to regulate water quality while eliminating drug residues.

3. Nutritional Hemorrhagic Disease

3.1 Causes

3.1.1 Vitamin deficiency

Experiments have proven that insufficient vitamin supplementation in feed, or production process issues, or improper feed storage causing vitamin deficiency in feed, can cause hemorrhage in fish. When fish are deficient in vitamin C, blood vessel permeability increases, and under stress conditions, peripheral blood vessels develop non-rupture skin hemorrhage; vitamin K deficiency prolongs blood coagulation time. In addition, deficiency of vitamin E, vitamin B2, etc. in fish may also manifest hemorrhagic symptoms.

3.1.2 Addition of olaquindox and flavomycin

Olaquindox, as an antibacterial growth-promoting drug, has obvious growth-promoting effects and can play a hormone-like role. If used in large quantities or for a long time, it produces strong side effects, such as poor anti-stress ability, fish being prone to injury and hemorrhage, intolerance to seining, high mortality during transport, and decreased disease resistance. Moreover, olaquindox has cumulative toxicity; when young fish are fed feed containing olaquindox, its side effects only become apparent at the adult fish stage. The state has already banned the addition of olaquindox to aquatic feed. Although the Ministry of Agriculture permits the addition of appropriate amounts of flavomycin to feed, the phenomenon of decreased anti-stress ability can also occur, especially when used in combination with olaquindox, the toxicity is enhanced.

3.2 Prevention and Treatment Measures

(1) Purchase high-quality feed produced by reputable feed manufacturers; generally, large reputable manufacturers will not have vitamin deficiencies or add prohibited drugs, while small manufacturers may cause vitamin deficiencies due to poor additive management or production process issues; (2) Feed requirements should be nutritionally complete and of reliable quality; add multivitamins to the feed every 15 days, for 4-5 consecutive days.

4. Stress-Induced Hemorrhagic Disease

4.1 Causes

In summer when water temperature is relatively high and water quality is poor, fish are startled by seining operations and undergo intense movement, endocrine activity intensifies, and oxygen consumption increases; after seining, water quality deteriorates further, dissolved oxygen in the water becomes severely insufficient, and a strong stress response occurs. It is mainly caused by factors such as hypoxia and bacterial toxins that lead to nervous system regulatory dysfunction, increased capillary permeability, and red blood cells leaking out of blood vessels through the vessel walls. Blunt snout bream (Wuchang bream) has relatively poor resistance but strong activity, making it more prone to stress responses.

4.2 Prevention and Treatment Measures

(1) Generally, strengthening water quality regulation before seining, disinfecting the water body, and increasing the feeding of vitamin C can effectively prevent it; (2) When formulating feed, add anti-stress drugs for fish per ton of compound feed; (3) During the farming process, focus on water quality regulation and improve fish immunity through various means.