How to prevent stress-induced hemorrhagic disease in fish? Detailed explanation of its incidence characteristics
Incidence characteristics and preventive measures of stress-induced hemorrhagic disease in fish
With the highly intensive development of the aquaculture industry, farmed fish are facing the influence of an increasing number of stress factors. In particular, in recent years a stress-related disease of fish with hemorrhage as the main symptom has emerged in aquaculture, bringing serious economic losses to production. The disease mainly manifests as follows: when farmed fish are stimulated by stress factors (such as seine netting and capture, sudden weather changes and long-distance transport, etc.), systemic body surface and gill hemorrhage can suddenly and rapidly occur, leading to mass mortality.
The causes of stress-induced hemorrhagic disease in fish are relatively complex, and prevention and treatment are difficult. According to pathological research and analysis, the disease is a non-infectious disease.
I. Incidence characteristics
1. There is no seasonality to its incidence; it can occur in all four seasons. The peak incidence period is from July to October, with the most severe cases occurring in the heat of midsummer; it mostly occurs when the water temperature is above 25°C, with the most severe cases at 28-32°C, and it rarely occurs below 20°C; in fish with stress-induced hemorrhage, as the water temperature gradually decreases, the symptoms gradually lessen or even disappear.
2. It can occur in various farmed fish, but it is most prominent in common carp, followed by grass carp, crucian carp, bream and silver carp and bighead carp. It can occur from the fingerling stage to the adult fish stage, but the incidence rate is generally high in adult fish.
3. This disease mostly occurs in aquaculture operations mainly feeding feeds with high nutritional content such as protein and energy, and it occurs under stimulation by stress factors, such as fish pond division, transfer between ponds, transfer between cages, and capture and long-distance transport during sales.
4. This disease is mostly seen in high-density culture ponds and cages, while it rarely occurs under culture conditions with lower density, lower feed quality and higher crude fiber content. In particular, after excessive feeding of feed supplemented with quinocetone, the incidence rate increases and the condition becomes more severe.
5. In fish ponds in the same area or cages in the same water body, when several feeds produced by different manufacturers are fed, or when feed from the same manufacturer is fed, only some fish develop the disease while others do not.
6. Affected fish generally grow faster than unaffected fish; even in the same affected fish pond or cage, the faster-growing, plump fish are more severely affected, while smaller, thinner fish are less affected or even unaffected.
7. Treatment of diseased fish with antibiotics is ineffective or only slightly effective; use of vitamin C, E and the like has some effect, but it is not ideal.
8. Onset is sudden. Before onset, the fish body shows no abnormal signs, but when the fish are stimulated by stress factors, symptoms often appear within a few minutes, a dozen minutes or a few tens of minutes, and death follows quickly, showing that the fish have extremely poor stress resistance.
II. Main symptoms
In most cases there is no obvious abnormality in the fish body, but once seine netting, capture or transport occurs, the fish body becomes very sensitive, extremely restless and jumps violently; within tens of seconds to a few minutes, the abdomen, head, corners of the mouth, operculum, gill filaments and bases of the fins of the fish body become noticeably congested, red and hemorrhagic. In severe cases, the gill filaments bleed severely, and large amounts of fresh blood gush out from under the operculum and redden the water body. Diseased fish are especially intolerant of long-distance transport, and most die during transport; even those that do not die appear critically ill, with the whole body turning peach-red and the fish body becoming stiff, ultimately dying or losing commercial value.
The body surface mucus secretion of diseased fish decreases, and it feels rough to the touch; muscle moisture increases, and the body surface appears edematous; the anus is mildly red and swollen, and the intestine is mildly congested; the liver is enlarged and brittle in texture; the gallbladder is distended and filled with bile; the spleen is congested and enlarged, appearing purplish-black; the heart is mildly enlarged and paler in color; and there is varying amounts of pale yellow ascites accumulated in the abdominal cavity.
III. Preventive measures
1. Compound feed formulas should be nutritionally balanced. Feed different proportions of feed during different growth stages of fish, especially with protein content just right and in appropriate proportion. Control the use of growth hormones of the quinocetone type (50 grams/ton of feed).
2. Appropriately supplement with natural bait, such as forage grass and snails.
3. Do not abuse highly irritating drugs; it is advisable to choose drugs with low irritation, good efficacy and a wide range of applicability, such as chlorine dioxide, dibromohydantoin, bromochlorohydantoin, and Chinese herbal preparations and biological preparations, so as to avoid long-term stimulation of the fish body that leads to poor stress resistance.
4. Avoid capture and transport during high-temperature periods. During capture and transport, movements should be slow and gentle, and soft nets and transport tools should be used.
5. When weather changes suddenly, make arrangements for water quality regulation, oxygenation and cooling in fish ponds, so as to predict early and prevent early.
6. Stocking density should not be too high; adopt ecological aquaculture methods to improve the environment for fish survival and growth and enhance the stress resistance of fish.
The causes of stress-induced hemorrhagic disease in fish are relatively complex, and prevention and treatment are difficult. According to pathological research and analysis, the disease is a non-infectious disease.
I. Incidence characteristics
1. There is no seasonality to its incidence; it can occur in all four seasons. The peak incidence period is from July to October, with the most severe cases occurring in the heat of midsummer; it mostly occurs when the water temperature is above 25°C, with the most severe cases at 28-32°C, and it rarely occurs below 20°C; in fish with stress-induced hemorrhage, as the water temperature gradually decreases, the symptoms gradually lessen or even disappear.
2. It can occur in various farmed fish, but it is most prominent in common carp, followed by grass carp, crucian carp, bream and silver carp and bighead carp. It can occur from the fingerling stage to the adult fish stage, but the incidence rate is generally high in adult fish.
3. This disease mostly occurs in aquaculture operations mainly feeding feeds with high nutritional content such as protein and energy, and it occurs under stimulation by stress factors, such as fish pond division, transfer between ponds, transfer between cages, and capture and long-distance transport during sales.
4. This disease is mostly seen in high-density culture ponds and cages, while it rarely occurs under culture conditions with lower density, lower feed quality and higher crude fiber content. In particular, after excessive feeding of feed supplemented with quinocetone, the incidence rate increases and the condition becomes more severe.
5. In fish ponds in the same area or cages in the same water body, when several feeds produced by different manufacturers are fed, or when feed from the same manufacturer is fed, only some fish develop the disease while others do not.
6. Affected fish generally grow faster than unaffected fish; even in the same affected fish pond or cage, the faster-growing, plump fish are more severely affected, while smaller, thinner fish are less affected or even unaffected.
7. Treatment of diseased fish with antibiotics is ineffective or only slightly effective; use of vitamin C, E and the like has some effect, but it is not ideal.
8. Onset is sudden. Before onset, the fish body shows no abnormal signs, but when the fish are stimulated by stress factors, symptoms often appear within a few minutes, a dozen minutes or a few tens of minutes, and death follows quickly, showing that the fish have extremely poor stress resistance.
II. Main symptoms
In most cases there is no obvious abnormality in the fish body, but once seine netting, capture or transport occurs, the fish body becomes very sensitive, extremely restless and jumps violently; within tens of seconds to a few minutes, the abdomen, head, corners of the mouth, operculum, gill filaments and bases of the fins of the fish body become noticeably congested, red and hemorrhagic. In severe cases, the gill filaments bleed severely, and large amounts of fresh blood gush out from under the operculum and redden the water body. Diseased fish are especially intolerant of long-distance transport, and most die during transport; even those that do not die appear critically ill, with the whole body turning peach-red and the fish body becoming stiff, ultimately dying or losing commercial value.
The body surface mucus secretion of diseased fish decreases, and it feels rough to the touch; muscle moisture increases, and the body surface appears edematous; the anus is mildly red and swollen, and the intestine is mildly congested; the liver is enlarged and brittle in texture; the gallbladder is distended and filled with bile; the spleen is congested and enlarged, appearing purplish-black; the heart is mildly enlarged and paler in color; and there is varying amounts of pale yellow ascites accumulated in the abdominal cavity.
III. Preventive measures
1. Compound feed formulas should be nutritionally balanced. Feed different proportions of feed during different growth stages of fish, especially with protein content just right and in appropriate proportion. Control the use of growth hormones of the quinocetone type (50 grams/ton of feed).
2. Appropriately supplement with natural bait, such as forage grass and snails.
3. Do not abuse highly irritating drugs; it is advisable to choose drugs with low irritation, good efficacy and a wide range of applicability, such as chlorine dioxide, dibromohydantoin, bromochlorohydantoin, and Chinese herbal preparations and biological preparations, so as to avoid long-term stimulation of the fish body that leads to poor stress resistance.
4. Avoid capture and transport during high-temperature periods. During capture and transport, movements should be slow and gentle, and soft nets and transport tools should be used.
5. When weather changes suddenly, make arrangements for water quality regulation, oxygenation and cooling in fish ponds, so as to predict early and prevent early.
6. Stocking density should not be too high; adopt ecological aquaculture methods to improve the environment for fish survival and growth and enhance the stress resistance of fish.