Prevention and treatment of fish diseases and scientific use of drugs

With the continuous development of aquaculture, the scale of aquaculture continues to expand, the density of aquaculture increases greatly, and the flow of fry and parent fish between regions becomes more frequent, which makes the spread of aquaculture diseases more and more serious. Aquatic animal disease has become a serious problem threatening the aquaculture industry. In particular, the use of a large number of antibiotics, excessive and long-term use of the same insecticide make pathogens continue to enhance drug resistance, so that the use of fish disease prevention and control drugs continue to upgrade, causing a lot of economic losses to farming units. In order to popularize the prevention and treatment of fish diseases, this paper mainly introduces some basic knowledge of the use of fish medicine and general matters needing attention in the use of fish medicine.

One. Correct diagnosis and timely medication

In the process of diagnosis of fish disease, it is necessary to find out the cause of fish disease and master the conditions of the disease. Any disease occurs for a reason. There are three main causes of fish disease: one is external adverse stimulation, including mechanical damage, physical or chemical stimulation and pathogen infection; the other is malnutrition and lack of some essential nutrients; the second is the defect of the body itself. The occurrence of any kind of disease requires not only certain internal causes, but also certain external conditions, which are often referred to as the three pathogenic factors: the body itself, the pathogen and the environment. Among them, pathogens play a major role in the occurrence of disease, because it determines the occurrence of disease and the basic characteristics of disease; conditions can affect the role of pathogen, although it can not cause disease, but can promote or hinder the occurrence and development of disease.

A correct understanding of the causes and conditions of the disease can help us to understand the nature of the disease and formulate effective treatment and preventive measures. It is necessary to accurately diagnose fish diseases. First of all, it is necessary to have a full understanding of the ecological conditions, water quality and feeding conditions of the pond in order to correctly grasp the external causes of the disease; in addition to visual inspection, it is best to make further examination, through anatomy and microscopic examination, combined with the symptoms of diseased fish. in order to make a correct diagnosis of fish disease. Generally speaking, different fish diseases show different symptoms, but some fish disease symptoms are similar or the same, such as VC, VB2 deficiency and fulminant hemorrhagic disease and severe fish liver disease all show bleeding symptoms. Fish diseases with similar or similar symptoms should be carefully identified, and only after diagnosis can we prescribe the right medicine to the case.

For the affected ponds, medication should be given in time after diagnosis, and do not delay time. Because fish live in water, some of its activities are not easy for us to grasp, and the same is true after illness. Once diseased fish are found, their appetite has often decreased, which adds some difficulties to treatment. if measures are not taken immediately to control the disease, the diseased fish are likely to die because of the aggravation of the disease, and the pathogen will also take the opportunity to speed up the spread. in serious cases, it is likely to spread throughout the pond, with serious consequences. Only in the early stage of fish disease, sick fish still have a certain feeding capacity, timely feeding bait, can be treated in the fish body. Otherwise, it is not easy to control the disease by using external drugs to disinfect the pond water body. Although it is important for the treatment of bacterial and viral fish diseases, it also plays an important role in preventing secondary infection of invasive fish diseases.

Two. symptomatic selection and correct use of drugs

Any kind of drug can not cure all diseases. If it is not used properly, it can not only prevent and cure the disease, but may even aggravate the disease and cause greater economic losses. Different fish medicines can only be effective for different fish diseases. Generally speaking, antibacterial drugs should be taken internally and externally eliminated for bacterial fish diseases, while parasitic diseases should be sprinkled or bathed with insecticidal drugs in the whole pool. When choosing fish drugs, care should be taken to avoid the long-term use of the same drug to prevent and cure a certain kind of disease, so as not to make pathogens become resistant to drugs, resulting in reduced efficacy or even inefficacy. At the same time, attention should also be paid to the reliability and safety of drugs, some of which are highly enriched in organisms, such as hormones, antibiotics, mercurous nitrate, formalin and so on. The use of these drugs will directly affect the quality of fish products and human health. Special attention should be paid to the reasonable arrangement of withdrawal period or the replacement of drugs with less side effects and toxicity and less curative effect. Therefore, attention should be paid to the feasibility of drug use when choosing drugs. In addition, the selected drugs should pay attention to the adaptability of cultured species to drugs, such as trichlorfon is often used in silver carp, bighead carp, grass, carp and so on, but can not be used in California perch and freshwater Pomfret. In addition, different fishes have different responses to the same drug at different growth stages. Fishes such as grass and silver carp are more sensitive to copper sulfate and can be killed when the concentration is more than 1 mg / L, while freshwater Pomfret has no abnormal reaction when its concentration reaches 5 mg / L. the fry of grass and silver carp are more sensitive to copper sulfate and bleaching powder than adult fish, so they should be used carefully when disinfecting.

In the future, the development direction of fish drugs is "three-effect" high efficiency, quick effect, long-term effect; "three small" toxicity, small side effects, low dose and no "three causes" teratogenic, carcinogenic, mutagenic and Chinese herbal medicine. If there are conditions, it is appropriate to choose new drugs, but we should proceed from the local reality, consider the source, price and actual effect and other factors, not blindly choose and purchase, we should choose the products of formal manufacturers, so as to avoid losses.

3. Combination of drugs and reasonable compatibility

In most cases, when drugs are used in combination, that is, when two or more drugs are used at the same time, the effects of one or two drugs are always affected, and the synergistic effect can enhance the efficacy, while the antagonism can reduce the efficacy. Some will also produce toxicity and cause harm to the fish. Therefore, in the combined use of drugs, it is necessary to make use of the synergistic effect between drugs to avoid incompatibility. Generally speaking, the above synergistic or antagonistic effects will also occur when many antibiotics are used together. Antimicrobials can be divided into two categories according to their functional properties: the first category is bactericidal antibiotics. Including penicillin series, cephalomycin, aminoglycosides, bacitracin, and polymyxin, etc.; the second category is bacteriostatic antibiotics. Including chloramphenicol, tetracycline, erythromycin, oxytetracycline and sulfonamide. When the first kind of antibiotics are used together, the bactericidal effect can be enhanced or added. When the second kind of antibiotics are used together, the bacteriostatic effect can be added, but there is no enhanced germicidal effect. The combination of the first class and the second kind of antibiotics can produce antagonistic effect. In addition, interactions may also occur when antibiotics are mixed with other drugs. For example, sulfonamides and trimethoprim (TMP), bromogerlae and potassium permanganate, hydrogen peroxide and glacial acetic acid, rhubarb and ammonia can increase efficacy, while tetracyclines and aluminum, magnesium, calcium, iron and other metal ions in antacid drugs can form chelates and make the intestines difficult to absorb, thus reducing the role of antibiotics. Special attention should be paid to this point.

Because fish medicine has its uniqueness in the way it is used. So the vast majority of external drugs, more or less will be affected by the water medium. When multiple drugs are used at the same time, the influence on each other is particularly obvious. For example, the commonly used quicklime is not only antagonistic to copper sulfate, bleaching powder and rich chlorine, but also affected by phosphorus or ammonium nitrogen in water. Similarly, phosphorus or ammonium nitrogen will also interact with quicklime to reduce fertilizer efficiency, so it should be staggered for 5 days before and after use in production. On the other hand, when quicklime meets trichlorfon, it will have the synergism of drugs, which can turn some trichlorfon into more toxic dichlorvos, which is the fundamental reason why our commonly used trichlorfon and flour alkali mixture can have high efficacy.

There is also a commonly used mixture of copper sulfate and ferrous sulfate, which also uses the synergy between drugs to give better play to its efficacy, but copper sulfate in alkaline water or when it meets with salt will produce antagonism between drugs and affect the efficacy. Therefore, in the comprehensive prevention and treatment of diseases of a variety of drugs, we must pay attention to their antagonism and cooperation, according to the specific situation, to determine the use of drugs and increase or decrease their doses.

Four. determination of drug dosage and rational administration

Because aquaculture animals live in a complex water environment, and physical and chemical factors such as temperature, salinity, pH, ammonia nitrogen and the content of organic matter (including dissolved and insoluble), as well as biological density (biomass), are important factors affecting drug efficacy. It is generally believed that the efficacy decreases with the increase of salinity and increases with the increase of temperature. Usually, the drug power can be doubled when the temperature increases by 10 ℃. The pH (pH) of water body also has different effects on different drugs. The effects of acidic drugs, anionic surfactants and chloramphenicol, tetracycline and furans in alkaline water environment are weakened, while those of alkaline drugs (such as kanamycin) and cationic surfactants (such as bromogeramine) and sulfonamides increase with the increase of pH value of water. For example, in alkaline environment, the effect of bleaching powder is weakened because the hypochlorite is easy to dissociate into hypochlorite ion (OCl-). In addition to the above factors, the content of organic matter and biological density in water will also affect the drug effect. The emergence of a large number of organic matter can usually weaken the antibacterial effect of many drugs, especially chemical disinfectants. Therefore, the dosage of drugs should pay attention to the above problems.

The drug dosage is determined, and when calculating the total drug use, it should be calculated according to different administration methods, and the drug dose is the guarantee of the curative effect, so the calculation must be accurate.

External use of drugs should be calculated according to the volume of water, expressed as "mg / L" or "ppm". If 1 cubic meter of water contains 1 g of 1ppm, that is, 1 mg / L. The calculation of sprinkling pesticide in the whole pond requires accurate measurement of pond water area. when calculating the average water depth, the total measuring points should be not less than 10, and the average value should be calculated. The calculation of drug use in the medicine bath should be based on the water capacity of the medicine bath container.

Internal medicine is generally calculated according to the body weight of the fish, and the premise is to accurately grasp the stock of the treated fish. For example, 50 kilograms of fish take 4.5 grams of dysentery 7.5 grams; the other is calculated according to the drug content of the bait, such as 100 kilograms of bait adding 300 grams of dysentery, according to the fish intake, if the bait is 3% of the body weight of fish, it is equivalent to 4.5 grams of bait for every 50 kilograms of fish; if the bait is 5%, it is equivalent to 7.5 grams of dysentery for every 50 kilograms of fish. When the disease is serious, the food intake of fish is greatly reduced, and the drug content in the feed should be increased according to the actual feeding rate. To ensure that eating fish can get an adequate dose of treatment. As for the number of courses of treatment, it should be determined by the severity of the disease and the course of the disease, for serious, long-lasting diseases, it is necessary to use two to three courses of treatment, otherwise the treatment is not complete, easy to relapse, but also cause pathogens to produce drug resistance. When one drug fails to cure within one or a course of treatment, it is best to switch to another drug for the next treatment. Generally, a better therapeutic effect will be achieved.

Different methods of drug administration should be adopted according to the type of fish disease and the nature of the drug. Drugs for external use generally play a local role, while drugs used in vivo mainly play an absorptive role in addition to anthelmintic drugs and drugs for enteritis. These are two different methods of drug administration. In order to improve the curative effect, we should pay attention to the following points:

When sprinkling medicine, you should feed it first and then sprinkle it. The drugs used should be fully dissolved and sprinkled evenly throughout the pool after dilution. The insoluble drugs should be fully stirred, and the dregs should not be put into the fish pond to avoid fish poisoning. Sprinkling should start from the upwind and gradually sprinkle downwind to increase the uniformity of the liquid. When sprinkling, you should pay attention to safety and minimize the harm of drugs to the human body. The time of sprinkling should be flexibly controlled according to the changes of the weather to make it play the best effect. Generally, medication should be used before 11:00 or 3 pm on a sunny day, but stop in rainy days, and the efficacy is poor on cloudy days. Hot summer weather should avoid the hot noon, can be carried out before 9: 00 in the morning or in the evening, should pay attention to the early morning fish floating head or floating head just after the end of medication, except for oxygen enhancers.

When making oral bait, medicine and feed should be mixed evenly, at the same time, pay attention to the interaction between drugs and feed additives, the size of granules should be appropriate, stop feeding once or 1 day before feeding, and then feed the bait. After the recovery of diseased fish, the feeding amount should be gradually increased to a constant to avoid overeating after the recovery of diseased fish.

In addition, when a variety of fish diseases are complicated, drugs should be used reasonably according to the priority of the disease, generally, the harmful diseases should be treated first, and drugs can also be mixed to increase efficacy and reduce costs.