Prevention and control measures for fish diseases prone to occur during the rainy season and the correct use of fishing medicines
_Huang Pengdan
Q: What are the main fish diseases that occurred during the 2019 rainy season (May-July)? What are the similarities and differences with previous years?
Lu Liqun: Overall, the incidence of fish in the northern region of China from May to July slowly increased, and the mortality rate also gradually increased, reaching a peak of the whole year in July; the incidence and mortality rate in the southern region of China also increased month by month until the peak of morbidity and mortality in August. May-July is worth vigilance is a small number of specific and common diseases of fish, these diseases in May and July in the peak of the incidence of the year, to attract the attention of farmers, such as water mold disease, three generations of insect disease, wheel worm disease, stimulating cryptonucleosis, crucian hematopoietic organ necrosis, bacterial gill disease, bacterial enteritis, tilapia streptococcal disease. These common multi-morbidity have similar trends each year. Compared with previous years, the bacterial sepsis in the spring of 2019 had a wide range of effects, causing a high mortality rate for the winter fish in the pond; due to its impact, the physical recovery of the fish in the pond after entering the rainy season was not good, and the relative mortality rate increased slightly compared with previous years.
Q: In the face of fish diseases that may occur during the rainy season in 2020, how should farmers prevent them?
Lu Liqun: Fish disease prevention and control, still adhere to the principle of prevention first, under the premise of ensuring the quality and safety of aquatic products to carry out ecological prevention and control, the main measures are summarized as follows.
1. Standardize the transfer pond, pond and fingerling release operations The transfer pond, the pond and the fish fingerling stocking operation should be careful and meticulous, and it is best to use a soft nylon pull net to avoid abrasions and scales of the fish body, bringing opportunities to germ infection. Wintering fish ponds do not turn ponds as much as possible to minimize mechanical damage to fish bodies during fishing and transfer. Fish bodies are sterilized with salt baking soda mixtures, potassium permanganate or povidone iodine before falling into the pond.
2. Control density, strengthen management, and prevent frostbite Control the density of adult fish or fry in ponds to avoid hypoxia caused by excessive density; check the activity status, feeding status, water quality changes and weather changes of farmed fish to prevent outbreaks and epidemics of diseases.
3. Timely feeding, strengthening nutrition, and restoring physical fitness When the water temperature gradually rises, the amount of feeding is gradually increased according to the number of fish eaten, the size of the fish and the feeding capacity. At the same time, fishery multi-dimensional, immune polysaccharide preparations, etc. are appropriately added to the feed to enhance the physique of the fish and improve the autoimmunity of the fish. Feed high-quality feed and adjust the feeding amount according to the fish eating, weather, etc.
4. Pay attention to water quality improvement and bottom change of the food farm Sprinkle 1 time quicklime water in 15 to 20 days, and use quicklime 20 to 25 kg per mu of water surface. Use microbial preparations such as photosynthetic bacteria and EM bacteria once every half a month to improve water quality. Choose a weak oxidation type of bottoming product, and change the bottom once every half a month in and around the food field to prevent bottom odor and hypoxia.
Q: What principles should be followed in freshwater aquaculture ponds for disease control?
Lu Liqun: Once the disease occurs, it is necessary to carry out symptomatic treatment on the basis of accurate diagnosis. Treatments for typical diseases are recommended below.
1. Bacterial sepsis Water disinfectants generally use quicklime (25 to 30 grams per cubic meter of water, but the pH of water bodies is prohibited if it exceeds 8.5), bleaching powder (1 g per cubic meter of water), chlorine dioxide (0.2 to 0.3 grams per cubic meter of water), strong chlorine (0.3 to 0.4 grams per cubic meter of water), bromochlorohydantoin (0.03 to 0.04 grams per cubic meter of water body) and other whole pools. Any one drug can be selected, which can effectively kill pathogenic bacteria, of which the effect of splashing the whole pool with quicklime water is remarkable. For the cultivation of grass carp on large water surfaces, the medicine is given in the dense shallow water area or bait throwing area of grass carp by hanging basket hanging bag. The internal medication is enrofloxacin and florfenicol, either one can be selected, with reference to the national standard drug dosage. When taking drugs internally, fishing multi-dimensional can be appropriately added to enhance the disease resistance of the fish body.
2. Water mold disease In the fish fishing and stocking as far as possible to avoid fish injuries, if there is injury, anti-inflammatory sterilization measures should be taken, or simply do not stock injured fish. At the same time, we should pay attention to grasping a reasonable stocking density when stocking. At the beginning of the outbreak, table salt and baking soda can be used, and the dosage is 5 g /m 3 water sprinkled or soaked in the whole pool, which can treat water mold disease; the whole pool can also be sprinkled with water mold net or dithiocylomethane, the dosage is 50 ml / (mu · rice) and 100 ml / (mu · rice). Use 1 time per day, twice a day.
3. Parasitic diseases There are many types of parasitic pathogens, and different parasitic pathogens have different applicable drugs. Anchor loach, Chinese gill, oblique tube worm, wheel worm and bodous disease can be treated by 0.3 g/m3 ferrous sulfate or 0.5 g/m 3 copper sulfate plus 0.2 g/m3 ferrous sulfate whole tank for the treatment of anchor head loach, Chinese seabream, oblique tube worm, wheel worm and bodosiasis. Small melon insects are more resistant, with lime and sulfur mixture 3 to 5 g / m 3, plus enemy insects 0.3 g / m 3 whole pond spill, can also be controlled by Chinese herbal medicine, such as per acre of water surface with paprika 200 grams plus 100 grams of ginger slices boiled into 25 kg of liquid medicine sprinkled all over the pond for control.
Q: When freshwater aquaculture ponds are infested, the causes are often complex, how do you think we can achieve "symptomatic medicine", and how far are we from precision medicine?
Lu Liqun: "Symptomatic medication" refers to the use of drugs for diseases, which is characterized by the adoption of effective measures for specific problems. Now China has accumulated rich fish epidemiological data and disease prevention and control experience, and has a corresponding response plan for any aquatic disease, and there is more than 1 set, and disease prevention and control is fully capable and should be turned passive into active. Symptomatic treatment in a complex environment is nothing more than to compare and identify what causes are the main causes from the quantitative point of view, what measures can be taken to reduce or control the proliferation of the main pathogens, and at the same time to determine how to improve the immunity of the fish body. Medication based on symptomatic treatment is itself the category of precision medication. "Precision medicine" in the scientific sense refers to the use of national standard fishing drugs to solve the problem of aquatic diseases according to the overall situation analysis of breeding species, breeding environment, breeding mode, weather, hazards, etc. The idealized goal is to use the least and most rational drug treatment as possible to achieve the best therapeutic effect based on predicting the acceptance of adverse drug reactions in farmed animals. Standardized drug use technology is crucial to improving drug efficacy, so it is necessary to consider the influencing factors such as the drug itself, as well as for farmed animals, drug targets, drug suspension periods, environment, and consumers. Based on the existing accumulation of scientific research in China, it can be expected that the precision drug use technology for certain drugs and farmed species will be demonstrated and promoted during the "14th Five-Year Plan" period.
Q: What is the significance of the Fish Medicine Reduction Campaign? What are the stages it is divided into?
Lu Liqun: The Ministry of Agriculture and Rural Affairs is implementing the "five major actions" for green and healthy aquaculture of aquatic products in 2020, including the 2020 aquaculture drug reduction action plan. In 2020, it is planned that through the implementation of aquaculture drug reduction actions in various places, the use of veterinary drugs in promotion points will be reduced by more than 5% on average year-on-year, and the use of antibiotic veterinary drugs will be reduced by more than 10% year-on-year, forming a number of standardized technical achievements and drug reduction technology models. The level of standardized drug use by farmers has been significantly improved, the problem of veterinary drug residues in aquaculture animals has been initially alleviated, and the quality and safety level of aquaculture aquatic products has been steadily improved. Through the implementation of the 2020 aquaculture drug reduction action, it is planned to establish more than 300 promotion points for aquaculture drug reduction models. In these demonstration sites, according to the characteristics of aquaculture disease hazards and the actual situation of prevention and control, adhere to the principle of "prevention as the mainstay, prevention and control combined", focusing on the development of ecological breeding, the use of high-quality seedlings, strengthening disease prevention and control, guiding and standardizing the use of drugs and strengthening production management of five technical measures to reduce drug use. Therefore, China's aquatic drug reduction action has gone through the stage of research pilot and program formulation, and has officially entered the stage of model promotion, and there will be two stages of technological improvement and comprehensive popularization in the future. We are confident that under the unified deployment of the state, all parties will form a joint force and escort the healthy aquaculture of aquatic products through the reduction of fishery drugs.
Q: In recent years, what work has been done in the research and development and clinical application of fishing drugs in bulk freshwater fish systems? What research progress has been made?
Lu Liqun: We mainly focus on the key research tasks of the technical system of the bulk freshwater fish industry, both on the surface and on the surface. It mainly includes the development of diagnostic technology and clinical services for various diseases of bacteria, viruses, parasites and fungi, and participates in the training of scientific drug use technology and guidance of clinical drugs. The work on the point mainly includes the "Eleventh Five-Year Plan" We focus on the malachite green replacement problem, developed "Meiting" and "Mold" and other water mold disease prevention and control drugs; "Twelfth Five-Year Plan" we developed environment-friendly drugs around grass carp viral hemorrhagic disease, developed "blood stop" antiviral drugs; "Thirteenth Five-Year Plan" around crucian carp herpes viral hematopoietic organ necrosis, we screened and developed environmentally friendly drugs, has completed pharmacokinetic and pharmacodynamic research, and will soon enter clinical testing. Of course, as a member of the Expert Committee on Aquaculture Disease Prevention and Control of the Ministry of Agriculture and Rural Affairs and the vice chairman of the Fishery Medicine Branch of the Fisheries Society, I have also done my best to actively participate in various government-industry-university-research cooperation and make my due contribution to the cause of healthy aquaculture of aquatic products.
Q: What are the main parasitic diseases in aquaculture? Which types of parasitic diseases have been more severe in recent years?
Xi Bingwen: There are many parasitic species in aquaculture, and there are differences in parasitic diseases in different breeding species, breeding environments and breeding modes; common species are ringworm disease, three-generation insect disease, anchor head loach disease, ciliate disease, myxosporidiosis, microsporidiosis, etc. In the current freshwater aquaculture environment, multi-son melon worm disease, Honghu iodine bubble worm disease (crucian carp throat sporozoite disease), anchor head loach disease, shrimp liver and intestine cytozoasis are relatively serious. Multi-son melon worm disease is seriously harmful to crucian carp, grass carp, salmon and other species raised in cages in thin water bodies, mountain flowing water or lake reservoirs; the water temperature is 15 to 25 °C, the disease often develops rapidly, the treatment is more difficult, and the death rate is large. In recent years, laryngeal spore disease has been a serious hazard to the seed and adult fish of farmed silver carp, and the pathogen carried by the fry is more serious, and the incidence of morbidity and death from June to September is 30% to 80%. Anchorhead bream disease can harm crucian carp, grass carp, carp, silver carp, silver carp, mandarin fish, etc., and the incidence in pond culture is relatively high. The pathogen of shrimp hepatoborostomycosis is a microsporidium, which mainly parasitizes in the liver and pancreas and intestine, affecting the digestion, absorption and growth of shrimp, and the breeding environment and seed carrying pathogens are more common. However, in recent years, the industry has attached great importance to the quarantine of seedlings, which has achieved remarkable results in reducing the occurrence of diseases and improving the success rate of breeding.
Q: What parasitic diseases are currently more difficult to treat? What are the difficulties of treatment?
Xi Bingwen: Freshwater melon worm disease is relatively easy to control in closed static aquaculture water bodies, and can effectively prevent and control the occurrence of diseases through moderate fertilizer water and maintaining good plankton biomass. In open water bodies or large water surfaces, fish in vitro or water body medication is facing great challenges, even if it has a certain effect through short-term, high-dose external drug immersion, repeated infection of larvae in the water body after a few days, it is still difficult to control. There is currently no universally effective drug for internal medications.
In culture, the outbreak of laryngeal spore disease in silver crucian carp is often difficult to treat, on the one hand, the oropharynx of the onset fish is swollen and cannot take medicinal bait, on the other hand, the currently commonly used chlorphenidine hydrochloride has a poor killing effect on myxosporidium. There were no detailed data on the pharmacology of chlorphenidine hydrochloride on myxosporidium at home and abroad, and our team found in recent studies that the current dose of chlorphenidine hydrochloride had no effect on myxosporidium, and if the dose was increased, it was easy to cause fish poisoning.
Anchorhead loach disease in the past using water body splashed avermectin, dimethodium, permethrin, repeat once in 7 to 10 days, internal antibacterial drugs, can better control the disease. Currently, in some polyculture ponds of fish, shrimp and crabs, their use is restricted due to the toxicity of these drugs to crustaceans. It is suggested that biological control methods of prevention could be considered. In the larval stage, the anchorhead falter, like the sword water fleas and the zhe water fleas, lives freely in the water body, and reduces the number of larvae by feeding the species of zooplankton by feeding on the species of zooplankton to reduce the intensity of infection.
Q: Based on the incidence of parasitic diseases in recent years, which types of parasitic diseases do you think are more likely to be endemic in 2020? How can farmers prevent this?
Xi Bingwen: The occurrence of parasitic diseases in farmed fish in 2020 is still dominated by the species mentioned above. Due to the obstruction of the sale of commercial fish in winter, more pressure ponds, fewer pond mouths that are thoroughly cleaned and disinfected, slightly higher overall temperature in winter, and higher survival rate of parasitic eggs or sporangia, the occurrence of parasitic diseases will be generally more. Disease prevention recommends regular weekly sampling, especially at water temperature of 20 to 25 °C, the peak of most parasite hatching and reproduction; if the intensity of infection is found to be high, timely medication is used; small numbers of infections are generally not recommended, and frequent medication is avoided.
Q: What have you and your team done to prevent and control parasitic diseases? What research progress has been made?
Xi Bingwen: The team has recently carried out a lot of work in the parasitic myxosporidosis of the heterogeneous silver crucian carp, and systematically studied the histopathology of the disease, the transmission route of infection, early detection technology and prevention drugs. In the first time at home and abroad from the aquaculture pond sediment collected from the subsmoil of Su's tail gill, 15 species of radiosporidium were found and reported, 4 new species of named myxozoa were found, and the infection transmission routes of 4 kinds of crucian carp parasitic iodine vesicle disease and unipolar disease (Wu Li iodine vesicle worm, cultured iodine bollworm, Wang's unipolar worm, Wuhan unipolar worm) were discovered; the crucian carp suffering from laryngeal spore disease died due to severe anemia, inflammatory response and secondary infection, and the detection found that the myxosporid pathogen could recessively infect the ovaries, pseudogill, kidney, spleen and other tissues and organs. A more sensitive and effective detection method suitable for early infection was established; a plant essential oil was obtained by using ex vitro drug screening method to obtain a significant killing effect on mature spores; and a solution for the prevention and treatment of laryngeal sporozoite disease at different stages of crucian carp splash, fry, adult fish and parents was systematically developed.
Q: As a "green fishing medicine", Chinese herbal fishing medicine is increasingly widely used in the prevention and treatment of fishing diseases, what are the advantages of Chinese herbal fishing medicine? What chinese herbal medicines are commonly used in aquatic products at present?
Xi Bingwen: The green development of fisheries in the new era attaches more importance to ecological and healthy breeding and quality safety, and the prevention and control of aquaculture diseases also attaches more importance to prevention. Maintaining a good breeding environment, improving fish body immunity, and reducing the use of antibiotics and chemical inputs have increasingly become the mainstream direction.
Chinese herbal medicine is a traditional medicine in China, which has a long history in clinical application and is widely used in the prevention and control of human, animal and poultry diseases. Medicinal plants contain natural polysaccharides, alkaloids, acids, terpenes, saponins and flavonoids, etc., which have important insecticidal, bacteriostatic, anti-inflammatory, antioxidant and immune enhancement effects. The application of Chinese herbal medicine to the prevention and control of aquatic animal diseases has the advantages of natural green, environmental degradation and diverse functions. At present, there are 53 kinds of Chinese herbal medicines in the list of approved veterinary drugs for aquatic products, each with different efficacy. However, we must be clear that the application of Chinese herbal medicine in aquaculture also faces some challenges, such as the lack of in-depth pharmacological research of Chinese herbal medicine in aquatic animals, and the great difference in physiological functions of fish and mammals. The price of Chinese herbal raw materials is not cheap, the price of some Chinese herbal fishing medicine products on the market is ridiculously low, and some are products made of chinese herbal medicine residue after extraction, and the quality and effect are not guaranteed.
Q: In recent years, what work has been done in the development of Chinese herbal fishing medicines in bulk freshwater fish systems? What research progress has been made?
Xi Bingwen: In 2017, the bulk freshwater fish system added a position in the development of Chinese herbal fishing medicine products, and the team led by researcher Xie Jun of the Freshwater Fisheries Research Center undertook specific research and development tasks, and I myself participated in the specific research and development work as a backbone member. The team mainly focuses on the important parasitic and bacterial diseases of bulk fish in the opening of Chinese herbal fishing drugs, and the research and development is divided into three steps: elucidating the pharmacological effect of monomer compounds in Chinese herbal extracts, evaluating the effect of fish body compounding, and registering and declaring drugs. At present, the pharmacological effects of emodin, curcumin, resveratrol, carvacrol and other components in medicinal plant extracts such as rhubarb, knotweed and other medicinal plant extracts have been mastered in detail, and the effect is remarkable in antibacterial infection, antioxidant and killing of myxosporidium.
Q: The diseases that occur in the breeding pond are not necessarily caused by pathogens, and feed that is not suitable for the nutritional needs of fish will also cause insufficient nutrition or excess nutrition, resulting in the occurrence of certain nutritional diseases, reducing the physique of fish, and causing fish deaths when serious. Can you tell us about the main nutritional diseases? How should farmers identify and control them?
Liao Shengchen: Fish as a cultured organism, need to obtain organic matter from the outside to meet their own growth and reproduction needs, so the level of feed nutritional value and whether the nutritional mix is balanced basically determines the growth rate and health of fish, feed quality has a pivotal role in healthy breeding. There are several common nutritional disorders.
1. Fatty liver disease Fish is born with diabetic animals, different species and great differences, most of the demand for sugar is limited, if the feed energy protein ratio is too high, there is a glucose metabolism disorder, the excess part of the synthesis of fat, causing visceral fat accumulation, hindering its normal function. The symptoms are that the fish body is short and the stomach is large, and after dissection, it is found that the abdominal cavity is full of fat, the fish has poor physique, is prone to death, is not tolerant of long-distance transportation, and is prone to death overwintering. The prevention and control method is to select a nutritionally balanced compound feed and abandon high-energy and low-protein feed.
2. Liver bad disease The causes are feed oxidation, rancidity, mold and deterioration. Fat is a substance that is easily oxidized, and the aldehydes, ketones and acids produced by fat oxidation are toxic to fish, which will directly damage the liver, causing diffuse steatosis to affect liver function, making the liver yellow or yellow-brown. The symptom is a large necrosis of hepatocytes, resulting in the accumulation of ascites in the fish body cavity. The prevention and control method is to add a certain amount of choline to the feed and feed the liver protection drugs.
3. Anemia The cause is the lack of essential vitamins and mineral elements in the feed, pollution poisoning. Symptoms are pale or pale pink gills, lack of oxygen due to insufficient blood supply, and symptoms of floating heads. The prevention and control method is to select feed with comprehensive nutrition and reasonable proportions.
4. Hypochondriasis (square head disease) Phosphorus deficiency in feed can cause chondropathy. The content of dissolved effective phosphorus in water is extremely low, the phosphorus required by the fish body comes from the feed, and the fish body absorbs calcium and phosphorus synchronously, and the lack of phosphorus will affect the absorption of calcium, resulting in the so-called "chondropathy". The symptom is a maclamental deformation of the skull and vertebrae, and the skull is square due to deformation, so it is also called square head disease. Adding an appropriate amount of calcium dihydrogen phosphate (not less than 1% of the feed amount) to the feed can prevent the occurrence of this disease.
5. Fish malformations The main cause is a lack of vitamin C, which may be insufficient amount of vitamin C added in the feed, or it may be unstable vitamin C that is not protected. The symptom is that the fish's spine becomes S-shaped, affecting the growth and appearance of the fish. The method of prevention and control is to add aquatic vitamins to the feed.
The occurrence of fish diseases is often not simply the lack of nutrients in one aspect, but the superposition of multiple factors, which needs to be comprehensively judged and actually solved. In order to avoid the occurrence of nutritional diseases, farmers should pay attention to when selecting and using feed, one is to try to choose products from large companies, market reputation and quality assurance, the second is to choose specific varieties, nutritious and balanced products, and the third is to select and use fresh products with a relatively recent production date.