What are the precautions for treating fish diseases? Keep these points in mind
Precautions for treating fish diseases
Precautions for treating fish diseases
In the prevention and treatment of diseases of fish, shrimp and shellfish, the long-term and repeated use of the same drug causes a decline in efficacy or even complete ineffectiveness; the appearance of this phenomenon is often called drug resistance. In recent years, countries around the world have attached great importance to this phenomenon, and the United Nations World Health Organization and the Food and Agriculture Organization have even established dedicated bodies to study countermeasures. According to statistics from relevant departments, more than 400 types of agricultural, fishery and public health pests and diseases worldwide have so far developed serious drug resistance (not including microbial drug resistance). Under natural conditions, some pests and diseases are more than 2,700 times resistant to organophosphorus drugs, and under indoor conditions some have drug resistance as high as more than 10,000 times. In China, over the past 40 years, pest and disease drug resistance in fish farming has also been quite serious. In the early 1960s, generally using 2.5% trichlorfon powder at 0.5-1 mg/L to kill crustacean parasites had significant efficacy; by the 1980s, some areas switched to more than 90% crystal trichlorfon yet still saw no good results. In some areas, chloramphenicol, oxytetracycline and others began to be used to prevent and treat bacterial diseases of fish, shrimp and shellfish with fairly high efficacy, but in recent years, in some areas, the use of these antibiotics to prevent and treat fish, shrimp and shellfish diseases has had low or even no efficacy. Fishermen in various places also report that the dosage per unit area of these antibiotics increases year by year, while the efficacy decreases year by year. In recent years, the author has carried out a certain amount of exploration in this area.
I. Causes of drug resistance
Drug resistance is the result of interaction between organisms and chemical drugs. The degree of drug resistance is generally expressed by comparing the virulence of a sensitive strain or the strain from when the drug was first used with that of a resistant strain. Investigation and testing results from Jiangsu, Fujian, Hunan, Hubei, Anhui and other places show:
1. Due to long-term, repeated use of the same drug. All kinds of organisms have the instinct to defend against harsh external environments. Under conditions of continuous exposure to drugs, fish pathogens, including bacteria and parasites, will naturally develop a drug-resistant response.
Within a bacterial strain or pest population, due to individual differences, responses to fish drugs all vary. For example, the fish gill disease parasite Sinergasilus, individuals relatively sensitive to trichlorfon or a mixture of copper sulfate and ferrous sulfate generally die of poisoning within 48 hours after application; insensitive individuals can endure until death at 144 hours; but some individuals become paralyzed after poisoning and then revive, continuing to survive and reproduce. The offspring of insensitive individuals are basically also insensitive. Thus insensitive individuals gradually gain the advantage and form an insensitive population, namely a drug-resistant population. The formation of such a population is generally the result of repeatedly using the same drug over many years. For pests and diseases that produce multiple generations within a year, such as Sinergasilus, Lernaea, Dactylogyrus, Gyrodactylus and others, this is especially obvious. Some people try to solve this by increasing the dose or increasing the application frequency, achieving certain results, but such results can only be temporary. For example, in the Jiangsu-Zhejiang area, trichlorfon was previously generally applied once every 2-2 months or even half a year to kill Sinergasilus and others, preventing and treating the "nongshui" disease of fish, but in recent years it must be applied every 10 days, half a month, or in some cases only one week, and the dosage is gradually increasing, otherwise it is ineffective. As a result of such application, the number of surviving parasite individuals decreases, but these individuals have stronger drug tolerance. The population formed by their offspring has even stronger drug resistance, and ultimately the drug will become ineffective.
2. Caused by application techniques. Incorrect application techniques not only waste drugs and reduce efficacy, but also easily cause the occurrence of drug resistance. For example, uneven application: generally more drug is applied at the water surface and at the edges of the water body, where the drug concentration is high, while pathogens have fewer opportunities to be exposed to the drug. In addition, some drugs such as furazolidone and allicin have very low solubility; even bleaching powder is slightly soluble in water, so uneven distribution is extremely easy to produce, and this provides survival conditions for drug-resistant populations, especially the egg and spore stages of pathogens. Another issue is the application dose: due to worry about the safety of fish (such as when using copper sulfate, mercurous acetate, mercurous nitrate, etc.) or lack of application experience, doses below the specified level are often used, especially with antibiotics such as chloramphenicol, oxytetracycline, erythromycin and others; using too low a dose is particularly likely to induce mutation of drug-resistant bacterial strains. This not only fails to achieve the prevention and treatment goal, but also easily induces drug resistance in pathogens. In addition, the selection of drug formulations, application methods, and the biology of pests and bacteria all relate to the development of drug resistance.
3. Influence of rearing systems. Certain fish rearing systems, such as supplementary stocking, polyculture and restocking measures, very easily change the parasitic conditions of viruses, bacteria and pests, and expand the spread of drug-resistant populations. Investigations show that pathogens in many adult fish ponds are mostly transferred from fingerling ponds (including fingerlings transported from local or other areas), especially when rotating and polyculturing fingerlings or when sharing fish nets. In addition, feeding aquatic plants and water filling and drainage also easily bring in drug-resistant varieties of harmful organisms.
II. Preventive countermeasures for drug resistance
1. Carry out integrated prevention and treatment. First, thoroughly clear the pond, and reasonably combine and mix species to change the parasitic hosts of pathogens; strengthen feeding management; fish stocking (including rotational stocking and restocking), bait feeding and water quality must all be strictly disinfected; master accurate application doses and application techniques; and regularly inspect pathogens and monitor drug resistance, so that before existing drugs become ineffective against certain pathogens, countermeasures such as rotating or replacing drugs can be formulated.
2. Rotate drugs. Do not use a single variety of drug for a long time, as this can cut off the formation of drug-resistant pathogen populations. For rotation, choose drugs with different mechanisms of action as much as possible. For example, for Sinergasilus, water centipedes and others, miechongjing, miechongling, or trichlorfon can be used; for white head and white mouth disease caused by Trichodina, miechongling, mancozeb, dichlorvos or sodium chloride can be used; for rotten gills complicated with pain caused by Dactylogyrus, Gyrodactylus and others, changteling and other drugs can be used, all with relatively good results.
3. Use Chinese herbal medicines. Chinese herbal medicines have wide sources, are convenient to obtain, save costs, and are less likely to produce drug resistance. They are relatively ideal methods for disease prevention and treatment. For example, pine needles tied into bundles and placed in water can prevent and treat fish lice, Lernaea and others; bitter herbs can prevent and treat parasitic gill diseases, Lernaea, Sinergasilus, Gyrodactylus, Dactylogyrus and others; smartweed can prevent and treat Sinergasilus, fish lice and others; but no drug-resistant populations have been found to develop in any case.
4. Mixed drug use. Reasonable mixed drug use can not only treat both pests and diseases, increase efficacy, and reduce costs, but also clearly overcome and inhibit the development of drug resistance. For example, among 190 new drugs recommended for agriculture in the United States, 28 are mixed formulations. The commonly used mixed use of copper sulfate and ferrous sulfate in China's fishery is an example. However, attention should be paid to the fact that drug combinations for mixed use must undergo careful research and must not be mixed blindly; confirmed mixed formulations also must not be used for a long time, and necessary drug rotation should be carried out to prevent harmful organisms from developing multiple resistance, that is, resistance to multiple drugs at the same time.
In the prevention and treatment of diseases of fish, shrimp and shellfish, the long-term and repeated use of the same drug causes a decline in efficacy or even complete ineffectiveness; the appearance of this phenomenon is often called drug resistance. In recent years, countries around the world have attached great importance to this phenomenon, and the United Nations World Health Organization and the Food and Agriculture Organization have even established dedicated bodies to study countermeasures. According to statistics from relevant departments, more than 400 types of agricultural, fishery and public health pests and diseases worldwide have so far developed serious drug resistance (not including microbial drug resistance). Under natural conditions, some pests and diseases are more than 2,700 times resistant to organophosphorus drugs, and under indoor conditions some have drug resistance as high as more than 10,000 times. In China, over the past 40 years, pest and disease drug resistance in fish farming has also been quite serious. In the early 1960s, generally using 2.5% trichlorfon powder at 0.5-1 mg/L to kill crustacean parasites had significant efficacy; by the 1980s, some areas switched to more than 90% crystal trichlorfon yet still saw no good results. In some areas, chloramphenicol, oxytetracycline and others began to be used to prevent and treat bacterial diseases of fish, shrimp and shellfish with fairly high efficacy, but in recent years, in some areas, the use of these antibiotics to prevent and treat fish, shrimp and shellfish diseases has had low or even no efficacy. Fishermen in various places also report that the dosage per unit area of these antibiotics increases year by year, while the efficacy decreases year by year. In recent years, the author has carried out a certain amount of exploration in this area.
I. Causes of drug resistance
Drug resistance is the result of interaction between organisms and chemical drugs. The degree of drug resistance is generally expressed by comparing the virulence of a sensitive strain or the strain from when the drug was first used with that of a resistant strain. Investigation and testing results from Jiangsu, Fujian, Hunan, Hubei, Anhui and other places show:
1. Due to long-term, repeated use of the same drug. All kinds of organisms have the instinct to defend against harsh external environments. Under conditions of continuous exposure to drugs, fish pathogens, including bacteria and parasites, will naturally develop a drug-resistant response.
Within a bacterial strain or pest population, due to individual differences, responses to fish drugs all vary. For example, the fish gill disease parasite Sinergasilus, individuals relatively sensitive to trichlorfon or a mixture of copper sulfate and ferrous sulfate generally die of poisoning within 48 hours after application; insensitive individuals can endure until death at 144 hours; but some individuals become paralyzed after poisoning and then revive, continuing to survive and reproduce. The offspring of insensitive individuals are basically also insensitive. Thus insensitive individuals gradually gain the advantage and form an insensitive population, namely a drug-resistant population. The formation of such a population is generally the result of repeatedly using the same drug over many years. For pests and diseases that produce multiple generations within a year, such as Sinergasilus, Lernaea, Dactylogyrus, Gyrodactylus and others, this is especially obvious. Some people try to solve this by increasing the dose or increasing the application frequency, achieving certain results, but such results can only be temporary. For example, in the Jiangsu-Zhejiang area, trichlorfon was previously generally applied once every 2-2 months or even half a year to kill Sinergasilus and others, preventing and treating the "nongshui" disease of fish, but in recent years it must be applied every 10 days, half a month, or in some cases only one week, and the dosage is gradually increasing, otherwise it is ineffective. As a result of such application, the number of surviving parasite individuals decreases, but these individuals have stronger drug tolerance. The population formed by their offspring has even stronger drug resistance, and ultimately the drug will become ineffective.
2. Caused by application techniques. Incorrect application techniques not only waste drugs and reduce efficacy, but also easily cause the occurrence of drug resistance. For example, uneven application: generally more drug is applied at the water surface and at the edges of the water body, where the drug concentration is high, while pathogens have fewer opportunities to be exposed to the drug. In addition, some drugs such as furazolidone and allicin have very low solubility; even bleaching powder is slightly soluble in water, so uneven distribution is extremely easy to produce, and this provides survival conditions for drug-resistant populations, especially the egg and spore stages of pathogens. Another issue is the application dose: due to worry about the safety of fish (such as when using copper sulfate, mercurous acetate, mercurous nitrate, etc.) or lack of application experience, doses below the specified level are often used, especially with antibiotics such as chloramphenicol, oxytetracycline, erythromycin and others; using too low a dose is particularly likely to induce mutation of drug-resistant bacterial strains. This not only fails to achieve the prevention and treatment goal, but also easily induces drug resistance in pathogens. In addition, the selection of drug formulations, application methods, and the biology of pests and bacteria all relate to the development of drug resistance.
3. Influence of rearing systems. Certain fish rearing systems, such as supplementary stocking, polyculture and restocking measures, very easily change the parasitic conditions of viruses, bacteria and pests, and expand the spread of drug-resistant populations. Investigations show that pathogens in many adult fish ponds are mostly transferred from fingerling ponds (including fingerlings transported from local or other areas), especially when rotating and polyculturing fingerlings or when sharing fish nets. In addition, feeding aquatic plants and water filling and drainage also easily bring in drug-resistant varieties of harmful organisms.
II. Preventive countermeasures for drug resistance
1. Carry out integrated prevention and treatment. First, thoroughly clear the pond, and reasonably combine and mix species to change the parasitic hosts of pathogens; strengthen feeding management; fish stocking (including rotational stocking and restocking), bait feeding and water quality must all be strictly disinfected; master accurate application doses and application techniques; and regularly inspect pathogens and monitor drug resistance, so that before existing drugs become ineffective against certain pathogens, countermeasures such as rotating or replacing drugs can be formulated.
2. Rotate drugs. Do not use a single variety of drug for a long time, as this can cut off the formation of drug-resistant pathogen populations. For rotation, choose drugs with different mechanisms of action as much as possible. For example, for Sinergasilus, water centipedes and others, miechongjing, miechongling, or trichlorfon can be used; for white head and white mouth disease caused by Trichodina, miechongling, mancozeb, dichlorvos or sodium chloride can be used; for rotten gills complicated with pain caused by Dactylogyrus, Gyrodactylus and others, changteling and other drugs can be used, all with relatively good results.
3. Use Chinese herbal medicines. Chinese herbal medicines have wide sources, are convenient to obtain, save costs, and are less likely to produce drug resistance. They are relatively ideal methods for disease prevention and treatment. For example, pine needles tied into bundles and placed in water can prevent and treat fish lice, Lernaea and others; bitter herbs can prevent and treat parasitic gill diseases, Lernaea, Sinergasilus, Gyrodactylus, Dactylogyrus and others; smartweed can prevent and treat Sinergasilus, fish lice and others; but no drug-resistant populations have been found to develop in any case.
4. Mixed drug use. Reasonable mixed drug use can not only treat both pests and diseases, increase efficacy, and reduce costs, but also clearly overcome and inhibit the development of drug resistance. For example, among 190 new drugs recommended for agriculture in the United States, 28 are mixed formulations. The commonly used mixed use of copper sulfate and ferrous sulfate in China's fishery is an example. However, attention should be paid to the fact that drug combinations for mixed use must undergo careful research and must not be mixed blindly; confirmed mixed formulations also must not be used for a long time, and necessary drug rotation should be carried out to prevent harmful organisms from developing multiple resistance, that is, resistance to multiple drugs at the same time.