Practical Techniques for Fish Disease Prevention and Treatment and Scientific Medication Methods
Fish Disease Prevention and Treatment and Scientific Medication
With the continuous development of the aquaculture industry, the scale of farming has continued to expand, farming density has increased substantially, and the movement of fry and broodstock between regions has become more frequent, making the spread of diseases among farmed aquatic animals increasingly serious. Diseases of aquatic animals have become a serious problem threatening the aquaculture industry. In particular, the application of large amounts of antibiotics and the excessive and long-term use of the same insecticide have continuously strengthened the drug resistance of pathogens, causing the medications used for fish disease prevention and treatment to be constantly upgraded, which has caused considerable economic losses to farming units. To popularize fish disease prevention and treatment techniques, this article mainly introduces some basic knowledge on the use of fish medicines and general precautions for their use.
I. Correct Diagnosis and Timely Medication
In the process of diagnosing fish diseases, it is necessary to identify the causes of the disease and understand the conditions under which it occurs. The occurrence of any disease has a cause. There are three main causes of fish diseases: one is adverse external stimulation, including mechanical injury, physical or chemical irritation, and pathogen infection; the second is malnutrition of the body, lacking certain essential nutrients; and the third is defects in the body itself. The occurrence of any disease requires not only certain internal causes but also certain external conditions. These are what people often call the three factors of disease: the body itself, the pathogen, and the environment. Among them, the pathogen plays the main role in the occurrence of disease, because it determines the occurrence of the disease and its basic characteristics; conditions can affect the role of the pathogen, and although they cannot cause disease, they can promote or hinder its occurrence and development.
A correct understanding of the causes and conditions of disease can help us understand the essence of the disease and formulate effective treatment methods and preventive measures. Fish diseases must be diagnosed accurately. First, there must be a full understanding of the pond's ecological conditions, water quality, and feeding conditions in order to correctly grasp the external causes of the disease. For diseased fish, in addition to visual inspection, further examination is best carried out; only through dissection and microscopic examination, combined with the symptoms of the diseased fish, can a correct diagnosis of the fish disease be made. Generally speaking, different fish diseases show different symptoms, but some fish diseases have similar or identical symptoms. For example, vitamin C and vitamin B2 deficiency, explosive hemorrhagic disease, and severe fish liver disease all show hemorrhagic symptoms. Fish diseases with similar or closely related symptoms must be carefully differentiated, and only after a confirmed diagnosis can the right medicine be prescribed.
For ponds where disease has already occurred, medication should be given promptly after diagnosis, and delays must not be allowed. This is because fish live in water, and some of their activities are not easy for us to observe, and the same is true of their condition after illness. Once diseased fish are found, their appetite has often already declined, which adds a certain difficulty to treatment. If measures are not taken immediately to control the condition, the diseased fish may well die as the illness worsens, and pathogens will also take the opportunity to spread faster, possibly spreading through the entire pond in severe cases and producing serious consequences. Only in the early stage of the disease, when diseased fish still have some feeding ability, can timely feeding of medicated bait allow treatment within the fish body. Otherwise, relying solely on external medicines to disinfect the pond water will make the disease difficult to control. This is important not only for treating bacterial and viral fish diseases but also plays an important role in preventing secondary infections in invasive fish diseases.
II. Selecting the Right Medicine for the Disease and Using It Correctly
No single medicine can cure all diseases. If used improperly, it may not only fail to prevent and treat disease but may even worsen it and cause greater economic losses. Different fish medicines can only be effective against different fish diseases. Generally speaking, bacterial fish diseases should be treated with antibacterial drugs by oral administration plus external disinfection; parasitic diseases should be treated by selecting antiparasitic drugs for whole-pond splashing or medicated baths. When choosing fish medicines, care should be taken to avoid long-term use of the same medicine to prevent and treat a certain disease or category of disease, so as to prevent pathogens from developing drug resistance, which can lead to reduced or even ineffective efficacy. At the same time, attention should also be paid to the reliability and safety of the medicine. Some medicines have a strong bioaccumulation effect in organisms, such as hormones, antibiotics, mercurous nitrate, and formalin. The use of such medicines will directly affect the quality of fish products and human health, and special attention should be paid to them. When using such medicines, a reasonable withdrawal period should be arranged, or another medicine with smaller side effects and toxicity but slightly weaker efficacy should be chosen as a substitute. Therefore, when selecting medicines, attention should be paid to the feasibility of their use. In addition, when choosing medicines, attention should be paid to the adaptability of the farmed species to the medicine. For example, trichlorfon is often used for silver carp, bighead carp, grass carp, and common carp, but cannot be used for largemouth bass or freshwater pompano. In addition, different fish species at different growth stages also respond differently to the same medicine. For example, grass carp, silver carp, and similar fish are relatively sensitive to copper sulfate, and a concentration above 1 mg/L can be lethal, while freshwater pompano still shows no abnormal reaction when the concentration reaches 5 mg/L; the fry of grass carp, silver carp, and similar fish are more sensitive to copper sulfate and bleaching powder than adult fish, so caution is needed when disinfecting fry.
The future development direction of fish medicines is the "three effects": high efficiency, quick effect, and long-lasting effect; the "three smalls": low toxicity, small side effects, and small dosage; and no "three causes": teratogenicity, carcinogenicity, and mutagenicity; and Chinese herbal medicines. When conditions permit, new medicines should be selected, but this should proceed from local realities and take into account factors such as source, price, and actual effect. Blind purchasing should be avoided, and products from legitimate manufacturers should be chosen to avoid losses.
III. Combined Medication and Rational Compatibility
In most cases, when medicines are used in combination, that is, when two or more medicines are used at the same time, the action of one or two medicines is always affected. The synergistic effect produced can enhance efficacy, while antagonism reduces efficacy, and some combinations may also produce toxicity and harm the fish body. Therefore, when using medicines in combination, the synergistic effects among medicines should be utilized and incompatibilities avoided. Generally speaking, when many antibiotic drugs are used together, the above-mentioned synergistic or antagonistic effects also appear. Antibacterial drugs can be divided into two categories according to their mode of action: the first category is bactericidal antibiotics, including the penicillin series, cephalosporins, aminoglycosides, bacitracin, and polymyxins; the second category is bacteriostatic antibiotics, including chloramphenicol, tetracycline, erythromycin, oxytetracycline, and sulfonamides. When first-category antibiotics are used together, the bactericidal effect is enhanced or additive. When second-category antibiotics are used together, the bacteriostatic effect can be additive, but no enhanced bactericidal effect appears. When first-category and second-category antibiotics are used together, antagonism may occur. In addition, when antibiotic drugs are mixed with other drugs, interactions may also occur. For example, sulfonamides with trimethoprim (TMP), benzalkonium bromide with potassium permanganate, hydrogen peroxide with glacial acetic acid, and rhubarb with ammonia water can produce synergistic effects and increase efficacy; while tetracyclines with metal ions such as aluminum, magnesium, calcium, and iron in antacids can form chelates that make intestinal absorption difficult, thereby reducing the effect of the antibiotic. Special attention should be paid to this point.
Because fish medicines have their own unique characteristics in methods of use, the vast majority of external medicines are more or less affected by the water medium. When multiple medicines are used at the same time, the mutual effects are especially obvious. For example, commonly used quicklime not only has an antagonistic effect with copper sulfate, bleaching powder, and chlorine-rich preparations, but is also affected by phosphorus or ammonium nitrogen in the water. Likewise, phosphorus or ammonium nitrogen will also react with quicklime and reduce fertilizer efficiency, so in production their use should be separated by 5~7 days. When quicklime meets trichlorfon, however, it produces a synergistic drug effect and can turn part of the trichlorfon into the more toxic dichlorvos. This is the fundamental reason why the commonly used mixture of trichlorfon and sodium carbonate can increase efficacy.
The commonly used mixture of copper sulfate and ferrous sulfate also uses synergy among medicines to better exert efficacy, but copper sulfate in alkaline water quality or when meeting table salt will produce antagonism among medicines and affect efficacy. Therefore, when multiple medicines are used in comprehensive disease prevention and treatment, close attention must be paid to their antagonism and synergy, and the methods of use and increases or decreases in dosage must be determined according to specific conditions.
IV. Determination of Dosage and Rational Administration
Because aquaculture animals live in a complex water environment, the physical and chemical factors of the water body, such as temperature, salinity, pH, ammonia nitrogen, and organic matter (including dissolved and undissolved forms), as well as biological density (biomass), are all important factors affecting drug efficacy. It is generally believed that drug efficacy decreases with rising salinity and increases with rising temperature. Usually, for every 10°C increase in temperature, drug potency can increase by about 1 time. The pH of the water body also has different effects on different drugs. Acidic drugs, anionic surfactants, and drugs such as chloramphenicol, tetracycline, and furans have weakened effects in alkaline water environments; while alkaline drugs (such as kanamycin), cationic surfactants (such as benzalkonium bromide), and sulfonamides have effects that increase with rising water pH. For another example, in an alkaline environment, bleaching powder has a weakened effect because the hypochlorous acid produced easily dissociates into hypochlorite ions (OCl-). In addition to the above factors, the organic matter content and biological density in the water body also affect drug effects. The large presence of organic matter can usually weaken the antibacterial effects of many drugs, especially chemical disinfectants. Therefore, the dosage of medicines should take these issues into account.
Once the dosage is determined, when calculating the total amount of medicine used, it should be calculated separately according to different administration methods. Dosage is the guarantee of efficacy, so it must be calculated accurately.
External medicines should be calculated according to the volume of water, expressed as "mg/L" or "ppm". For example, 1 cubic meter of water containing 1 gram of medicine is 1 ppm, that is, 1 mg/L. For calculating whole-pond splashing medication, the pond water area must be measured accurately, and when calculating average water depth, the total number of measurement points should be no fewer than 10, and their average value should be taken. For calculating medicated bath medication, the water capacity of the medicated bath container should be used as the basis.
Oral medicines are generally calculated according to fish body weight, and the premise is to accurately grasp the standing stock of the treated fish. For example, 50 kg of fish are given 4.5~7.5 g of furazolidone orally; another method is to calculate according to the amount of medicine contained in the feed. For example, 100 kg of feed is supplemented with 300 g of furazolidone and fed according to the fish's feeding amount. If feeding at 3% of fish body weight, this is equivalent to feeding 4.5 g of furazolidone per 50 kg of fish; if feeding at 5%, this is equivalent to feeding 7.5 g of furazolidone per 50 kg of fish. When the disease is severe, the feeding amount of fish is greatly reduced. At this time, the medicine content in the feed should be increased according to the actual feeding rate to ensure that feeding fish can obtain sufficient therapeutic dosage. As for the number of treatment courses used, this should be determined by the severity of the disease and the urgency of its course. For diseases that are severe and last a long time, it is necessary to use two to three treatment courses; otherwise, treatment will not be thorough, recurrence will be easy, and pathogens will also develop drug resistance. When one medicine fails to cure the disease within one administration or one treatment course, it is best to switch to another medicine at the next treatment. Generally, better therapeutic results will be obtained.
As for administration methods, different methods should be adopted according to the type of fish disease and the properties of the medicine. External medicines generally mainly exert local effects, while internal medicines, except anthelmintics and drugs for treating enteritis, mainly exert absorptive effects. These are two different administration methods. To improve efficacy, the following points should be noted during administration:
When splashing medicines, feed first and then splash the medicine. The medicines used should be fully dissolved and, after dilution, evenly splashed over the whole pond. Medicines that do not dissolve easily should be fully stirred, and the residue should not be put into the fish pond, so as to avoid fish accidentally eating it and being poisoned. Splashing should begin from the upwind area and gradually proceed downwind, so as to increase the uniformity of the medicinal liquid. During splashing, attention should be paid to safety and to minimizing harm to the human body from the medicines. The timing of splashing should be flexibly controlled according to weather changes so as to produce the best efficacy. Generally, medicine should be used before 11 a.m. or after 3 p.m. on clear days, stopped on rainy days, and less effective on cloudy days. In high-temperature summer weather, the hot midday period should be avoided, and it can be done before 9 a.m. or in the evening. Note that medicine cannot be used at the time fish are floating at the surface in the early morning or just as surface floating ends, except of course for oxygen-increasing agents.
When making oral medicated bait, the medicine and feed should be mixed evenly, and attention should also be paid to interactions between the medicine and feed additives. The size of the processed pellets should be suitable for feeding. Before feeding, feeding should be stopped once or for one day, and then the medicated bait should be fed. After the diseased fish recover, the feeding amount should be gradually increased to the normal amount to avoid overeating after the fish recover from illness.
In addition, when multiple fish diseases occur at the same time, medicines should be used rationally according to the severity and urgency of the condition. Generally, the more harmful disease should be treated first; medicines may also be used in combination to increase efficacy and reduce costs.
I. Correct Diagnosis and Timely Medication
In the process of diagnosing fish diseases, it is necessary to identify the causes of the disease and understand the conditions under which it occurs. The occurrence of any disease has a cause. There are three main causes of fish diseases: one is adverse external stimulation, including mechanical injury, physical or chemical irritation, and pathogen infection; the second is malnutrition of the body, lacking certain essential nutrients; and the third is defects in the body itself. The occurrence of any disease requires not only certain internal causes but also certain external conditions. These are what people often call the three factors of disease: the body itself, the pathogen, and the environment. Among them, the pathogen plays the main role in the occurrence of disease, because it determines the occurrence of the disease and its basic characteristics; conditions can affect the role of the pathogen, and although they cannot cause disease, they can promote or hinder its occurrence and development.
A correct understanding of the causes and conditions of disease can help us understand the essence of the disease and formulate effective treatment methods and preventive measures. Fish diseases must be diagnosed accurately. First, there must be a full understanding of the pond's ecological conditions, water quality, and feeding conditions in order to correctly grasp the external causes of the disease. For diseased fish, in addition to visual inspection, further examination is best carried out; only through dissection and microscopic examination, combined with the symptoms of the diseased fish, can a correct diagnosis of the fish disease be made. Generally speaking, different fish diseases show different symptoms, but some fish diseases have similar or identical symptoms. For example, vitamin C and vitamin B2 deficiency, explosive hemorrhagic disease, and severe fish liver disease all show hemorrhagic symptoms. Fish diseases with similar or closely related symptoms must be carefully differentiated, and only after a confirmed diagnosis can the right medicine be prescribed.
For ponds where disease has already occurred, medication should be given promptly after diagnosis, and delays must not be allowed. This is because fish live in water, and some of their activities are not easy for us to observe, and the same is true of their condition after illness. Once diseased fish are found, their appetite has often already declined, which adds a certain difficulty to treatment. If measures are not taken immediately to control the condition, the diseased fish may well die as the illness worsens, and pathogens will also take the opportunity to spread faster, possibly spreading through the entire pond in severe cases and producing serious consequences. Only in the early stage of the disease, when diseased fish still have some feeding ability, can timely feeding of medicated bait allow treatment within the fish body. Otherwise, relying solely on external medicines to disinfect the pond water will make the disease difficult to control. This is important not only for treating bacterial and viral fish diseases but also plays an important role in preventing secondary infections in invasive fish diseases.
II. Selecting the Right Medicine for the Disease and Using It Correctly
No single medicine can cure all diseases. If used improperly, it may not only fail to prevent and treat disease but may even worsen it and cause greater economic losses. Different fish medicines can only be effective against different fish diseases. Generally speaking, bacterial fish diseases should be treated with antibacterial drugs by oral administration plus external disinfection; parasitic diseases should be treated by selecting antiparasitic drugs for whole-pond splashing or medicated baths. When choosing fish medicines, care should be taken to avoid long-term use of the same medicine to prevent and treat a certain disease or category of disease, so as to prevent pathogens from developing drug resistance, which can lead to reduced or even ineffective efficacy. At the same time, attention should also be paid to the reliability and safety of the medicine. Some medicines have a strong bioaccumulation effect in organisms, such as hormones, antibiotics, mercurous nitrate, and formalin. The use of such medicines will directly affect the quality of fish products and human health, and special attention should be paid to them. When using such medicines, a reasonable withdrawal period should be arranged, or another medicine with smaller side effects and toxicity but slightly weaker efficacy should be chosen as a substitute. Therefore, when selecting medicines, attention should be paid to the feasibility of their use. In addition, when choosing medicines, attention should be paid to the adaptability of the farmed species to the medicine. For example, trichlorfon is often used for silver carp, bighead carp, grass carp, and common carp, but cannot be used for largemouth bass or freshwater pompano. In addition, different fish species at different growth stages also respond differently to the same medicine. For example, grass carp, silver carp, and similar fish are relatively sensitive to copper sulfate, and a concentration above 1 mg/L can be lethal, while freshwater pompano still shows no abnormal reaction when the concentration reaches 5 mg/L; the fry of grass carp, silver carp, and similar fish are more sensitive to copper sulfate and bleaching powder than adult fish, so caution is needed when disinfecting fry.
The future development direction of fish medicines is the "three effects": high efficiency, quick effect, and long-lasting effect; the "three smalls": low toxicity, small side effects, and small dosage; and no "three causes": teratogenicity, carcinogenicity, and mutagenicity; and Chinese herbal medicines. When conditions permit, new medicines should be selected, but this should proceed from local realities and take into account factors such as source, price, and actual effect. Blind purchasing should be avoided, and products from legitimate manufacturers should be chosen to avoid losses.
III. Combined Medication and Rational Compatibility
In most cases, when medicines are used in combination, that is, when two or more medicines are used at the same time, the action of one or two medicines is always affected. The synergistic effect produced can enhance efficacy, while antagonism reduces efficacy, and some combinations may also produce toxicity and harm the fish body. Therefore, when using medicines in combination, the synergistic effects among medicines should be utilized and incompatibilities avoided. Generally speaking, when many antibiotic drugs are used together, the above-mentioned synergistic or antagonistic effects also appear. Antibacterial drugs can be divided into two categories according to their mode of action: the first category is bactericidal antibiotics, including the penicillin series, cephalosporins, aminoglycosides, bacitracin, and polymyxins; the second category is bacteriostatic antibiotics, including chloramphenicol, tetracycline, erythromycin, oxytetracycline, and sulfonamides. When first-category antibiotics are used together, the bactericidal effect is enhanced or additive. When second-category antibiotics are used together, the bacteriostatic effect can be additive, but no enhanced bactericidal effect appears. When first-category and second-category antibiotics are used together, antagonism may occur. In addition, when antibiotic drugs are mixed with other drugs, interactions may also occur. For example, sulfonamides with trimethoprim (TMP), benzalkonium bromide with potassium permanganate, hydrogen peroxide with glacial acetic acid, and rhubarb with ammonia water can produce synergistic effects and increase efficacy; while tetracyclines with metal ions such as aluminum, magnesium, calcium, and iron in antacids can form chelates that make intestinal absorption difficult, thereby reducing the effect of the antibiotic. Special attention should be paid to this point.
Because fish medicines have their own unique characteristics in methods of use, the vast majority of external medicines are more or less affected by the water medium. When multiple medicines are used at the same time, the mutual effects are especially obvious. For example, commonly used quicklime not only has an antagonistic effect with copper sulfate, bleaching powder, and chlorine-rich preparations, but is also affected by phosphorus or ammonium nitrogen in the water. Likewise, phosphorus or ammonium nitrogen will also react with quicklime and reduce fertilizer efficiency, so in production their use should be separated by 5~7 days. When quicklime meets trichlorfon, however, it produces a synergistic drug effect and can turn part of the trichlorfon into the more toxic dichlorvos. This is the fundamental reason why the commonly used mixture of trichlorfon and sodium carbonate can increase efficacy.
The commonly used mixture of copper sulfate and ferrous sulfate also uses synergy among medicines to better exert efficacy, but copper sulfate in alkaline water quality or when meeting table salt will produce antagonism among medicines and affect efficacy. Therefore, when multiple medicines are used in comprehensive disease prevention and treatment, close attention must be paid to their antagonism and synergy, and the methods of use and increases or decreases in dosage must be determined according to specific conditions.
IV. Determination of Dosage and Rational Administration
Because aquaculture animals live in a complex water environment, the physical and chemical factors of the water body, such as temperature, salinity, pH, ammonia nitrogen, and organic matter (including dissolved and undissolved forms), as well as biological density (biomass), are all important factors affecting drug efficacy. It is generally believed that drug efficacy decreases with rising salinity and increases with rising temperature. Usually, for every 10°C increase in temperature, drug potency can increase by about 1 time. The pH of the water body also has different effects on different drugs. Acidic drugs, anionic surfactants, and drugs such as chloramphenicol, tetracycline, and furans have weakened effects in alkaline water environments; while alkaline drugs (such as kanamycin), cationic surfactants (such as benzalkonium bromide), and sulfonamides have effects that increase with rising water pH. For another example, in an alkaline environment, bleaching powder has a weakened effect because the hypochlorous acid produced easily dissociates into hypochlorite ions (OCl-). In addition to the above factors, the organic matter content and biological density in the water body also affect drug effects. The large presence of organic matter can usually weaken the antibacterial effects of many drugs, especially chemical disinfectants. Therefore, the dosage of medicines should take these issues into account.
Once the dosage is determined, when calculating the total amount of medicine used, it should be calculated separately according to different administration methods. Dosage is the guarantee of efficacy, so it must be calculated accurately.
External medicines should be calculated according to the volume of water, expressed as "mg/L" or "ppm". For example, 1 cubic meter of water containing 1 gram of medicine is 1 ppm, that is, 1 mg/L. For calculating whole-pond splashing medication, the pond water area must be measured accurately, and when calculating average water depth, the total number of measurement points should be no fewer than 10, and their average value should be taken. For calculating medicated bath medication, the water capacity of the medicated bath container should be used as the basis.
Oral medicines are generally calculated according to fish body weight, and the premise is to accurately grasp the standing stock of the treated fish. For example, 50 kg of fish are given 4.5~7.5 g of furazolidone orally; another method is to calculate according to the amount of medicine contained in the feed. For example, 100 kg of feed is supplemented with 300 g of furazolidone and fed according to the fish's feeding amount. If feeding at 3% of fish body weight, this is equivalent to feeding 4.5 g of furazolidone per 50 kg of fish; if feeding at 5%, this is equivalent to feeding 7.5 g of furazolidone per 50 kg of fish. When the disease is severe, the feeding amount of fish is greatly reduced. At this time, the medicine content in the feed should be increased according to the actual feeding rate to ensure that feeding fish can obtain sufficient therapeutic dosage. As for the number of treatment courses used, this should be determined by the severity of the disease and the urgency of its course. For diseases that are severe and last a long time, it is necessary to use two to three treatment courses; otherwise, treatment will not be thorough, recurrence will be easy, and pathogens will also develop drug resistance. When one medicine fails to cure the disease within one administration or one treatment course, it is best to switch to another medicine at the next treatment. Generally, better therapeutic results will be obtained.
As for administration methods, different methods should be adopted according to the type of fish disease and the properties of the medicine. External medicines generally mainly exert local effects, while internal medicines, except anthelmintics and drugs for treating enteritis, mainly exert absorptive effects. These are two different administration methods. To improve efficacy, the following points should be noted during administration:
When splashing medicines, feed first and then splash the medicine. The medicines used should be fully dissolved and, after dilution, evenly splashed over the whole pond. Medicines that do not dissolve easily should be fully stirred, and the residue should not be put into the fish pond, so as to avoid fish accidentally eating it and being poisoned. Splashing should begin from the upwind area and gradually proceed downwind, so as to increase the uniformity of the medicinal liquid. During splashing, attention should be paid to safety and to minimizing harm to the human body from the medicines. The timing of splashing should be flexibly controlled according to weather changes so as to produce the best efficacy. Generally, medicine should be used before 11 a.m. or after 3 p.m. on clear days, stopped on rainy days, and less effective on cloudy days. In high-temperature summer weather, the hot midday period should be avoided, and it can be done before 9 a.m. or in the evening. Note that medicine cannot be used at the time fish are floating at the surface in the early morning or just as surface floating ends, except of course for oxygen-increasing agents.
When making oral medicated bait, the medicine and feed should be mixed evenly, and attention should also be paid to interactions between the medicine and feed additives. The size of the processed pellets should be suitable for feeding. Before feeding, feeding should be stopped once or for one day, and then the medicated bait should be fed. After the diseased fish recover, the feeding amount should be gradually increased to the normal amount to avoid overeating after the fish recover from illness.
In addition, when multiple fish diseases occur at the same time, medicines should be used rationally according to the severity and urgency of the condition. Generally, the more harmful disease should be treated first; medicines may also be used in combination to increase efficacy and reduce costs.