What are the correct methods for selecting fishery drugs?

Aquaculture farmers should select fishery drugs or feed medication additives based on the pathogens of the cultured species and the instructions for the fishery drugs. The selected medicated feed additives should comply with the provisions of the "Regulations on the Administration of Feed and Feed Additives" (Annex 2). Drugs or additives prohibited by the state (Annex 3) must not be used, nor should feed with added antibacterial drugs be stored for long periods.

Before selecting fishery drugs, the disease should first be diagnosed, and then the fishery drugs should be accurately selected by considering the drug, pathogen, environment, the cultured animal itself, and human health.

The diagnosis of aquatic animal diseases should follow the procedures below:

(1) Sampling

1. For diseased aquatic animals, select individuals that are sick but not yet dead, or that have died only recently, and that show relatively typical symptoms, as subjects for diagnostic examination, and no fewer than 3 individuals; for diseases that cannot be immediately diagnosed, samples should be properly preserved. Fixatives and preservatives may be used to fix and preserve the whole body, partial organs or tissues, or pathogens of the diseased animals for further diagnosis.

2. Water samples from diseased culture facilities should be collected at the same time as the diseased aquatic animal samples are taken, and analyzed immediately.

(2) Observation and investigation

1. The cultured species, source, size, quality condition, and stocking density, etc.

2. The type, quality, dosage, and method of disinfectants used for culture facilities and equipment before stocking, etc.

3. The type and source of feed, feeding method, feeding amount, and removal of residual feed, etc.

4. The feeding and management situation of the aquatic animals.

5. Relevant environmental factors, such as water source, water quality, water temperature, substrate, and pesticide application in farmland around the culture water area, etc.

6. Observe the activity of the same and different species of aquaculture animals in diseased and non-diseased culture facilities, such as swimming, feeding, and resting.

7. The disease situation and previously adopted prevention and control measures, including the time of onset, diseased animals, symptoms and condition, mortality, and measures taken, etc.

8. The area, structure, soil quality, water depth, water color, transparency, water intake and drainage system, and whether bubbles float up in the diseased culture facilities.

(3) Pathogen identification

1. Visual inspection

(1) Observe with the naked eye whether there are changes in the color of the body and diseased organs (including gills) of the diseased aquaculture animals, whether there are pathological changes such as inflammation, congestion, hemorrhage, anemia, swelling, and ulcers, whether there are foreign objects attached, and the growth stage and developmental degree of the diseased individuals.

(2) Observe with the naked eye whether the diseased aquaculture animals are parasitized by fungi or parasites. If parasitism is found, species identification should be carried out.

2. Microscopic examination

(1) Use tweezers to scrape mucus from external organs such as skin, fins, and gills, or take a portion of diseased tissue, make a wet mount, and examine it under a microscope to look for pathogens and note pathological changes in the diseased tissue.

(2) Observe whether there is fungal or parasitic infestation. If parasitism is found, identification can generally be made from the morphology of the pathogen.

3. Anatomical examination

(1) Visually examine and dissect internal organs. First observe with the naked eye whether there are changes in the color and shape of internal organs and tissues, whether there are pathological changes such as inflammation, congestion, hemorrhage, swelling, ulcers, atrophy and degeneration, hypertrophy and hyperplasia, and coelomic fluid accumulation, and whether there are parasites and their cysts.

(2) Microscopic examination. Microscopically examine each organ and tissue. First draw blood from the heart for microscopic examination, then scrape mucus from the body cavity or other organ cavities for examination. For solid organs such as the liver and kidney, take a small piece of tissue and examine it by the compression method, and note whether there are pathological changes and pathogens.

4. Pathological section examination. Take a small piece of diseased tissue or organ, process it through procedures such as fixation, dehydration, and embedding, cut the sample into extremely thin slices, then stain it with the corresponding staining method to reveal different cells and cellular changes, and then perform optical microscope examination (electron microscopy is required for further observation).

5. PCR instrument detection. PCR instrument detection technology has been recommended by the World Organisation for Animal Health as one of the diagnostic methods for shrimp viruses. Viral diseases such as white spot syndrome in shrimp, as well as other aquatic animal diseases for which PCR diagnostic technology has been established, can be diagnosed by this method.

6. Nucleic acid probe detection. At present, nucleic acid probe hybridization detection methods for viruses such as IHHNV and HPV are available for detection.

7. Immunological technique detection. Techniques such as serum neutralization tests, immunofluorescence, and enzyme-linked immunosorbent assays can be selected for use.

8. Drug sensitivity test detection. For diseases possibly caused by bacteria, after tests such as pathogen isolation, culture, identification, and artificial infection, corresponding drug sensitivity tests can then be carried out.

(4) Diseases caused by multiple pathogens

Determine the main pathogenic pathogen according to the number of pathogens and the degree of harm, and then treat the symptoms accordingly.

(5) Principles for drug selection

1. Effectiveness

First, consider the therapeutic effect of a certain drug on a certain disease. Generally, the reduction in mortality after administration is used as the main basis for determining efficacy. In addition, comparisons must also be made with the control group in terms of feeding rate and weight gain rate, and the curative effect should be supported by histopathological evidence.

2. Safety

When selecting drugs, attention should be paid not only to their efficacy but also to their adverse reactions. Although some drugs are very effective, they have to be prohibited because of their relatively strong toxic side effects on cultured animals or potential harm to humans.

3. Convenience

Most human medicines and veterinary medicines are administered directly to individuals, while fishery drugs, except in a few cases where injection and smearing methods are used, are mostly administered indirectly to groups, by feeding medicated bait or putting drugs into the culture water for medicated baths. Therefore, convenient operation and easy mastery of usage and dosage are among the requirements for selecting fishery drugs.

4. Economy

Consider from two aspects: (1) Economic analysis of clinical medication. It is necessary to analyze whether the disease of the cultured animals can be cured after medication; after cure, the growth speed, product quality, @#@136@#@ price, etc. of the cultured animals, so as to determine the economic viability of medication. If medication can be avoided, it is best not to use it. (2) Select cheap and readily available drugs. Aquaculture has the characteristics of being extensive, dispersed, and large in area, and the overall amount of drugs is relatively large, especially for medicated bath treatment. Under the principles of ensuring efficacy and safety, cheap and readily available drugs should be selected.

(6) Selection of administration routes

1. Oral administration

Oral administration uses a small amount of drug, is convenient to operate, and does not pollute the environment. This method is often used to increase nutrition, aid recovery after illness, and treat internal pathogenic biological infections, especially bacterial enteritis and parasitic intestinal diseases. However, its therapeutic effect is affected by the condition of the cultured animals and their feeding ability. It is ineffective for individuals that are seriously ill and have lost feeding ability, and it is also somewhat difficult for filter-feeding species and species that feed on live food organisms.

2. Medicated bath method

According to the size of the medicated bath water body, it can be divided into the broadcast sprinkling method and the immersion washing method. According to the different concentrations and durations of immersion in the medicinal solution, it can be divided into instantaneous immersion, short-term immersion, long-term immersion, and flowing water immersion. The broadcast sprinkling method is a method often used in disease prevention and control. The immersion washing method uses a small amount of drug, is simple to operate, can be controlled manually, has a good control effect on pathogens on the body surface and gills, and has no effect on other organisms in the culture water body. It is currently a method often used in industrialized aquaculture. In artificial breeding production, brood fish, brood shrimp, brood shellfish, and their fertilized eggs purchased from other places or caught from natural water bodies can also be disinfected by the immersion washing method.

3. Injection method

There are two injection methods commonly used in fish disease prevention and control and induced spawning, namely intramuscular injection and intraperitoneal injection. This method has incomparable advantages such as accurate dosage, fast absorption, high efficacy (drug injection), and good preventive effect (vaccine and bacterin injection), but it is troublesome to operate and easily injures the fish body. Suitable subjects are those few and precious species, or parents used for breeding offspring. Antibiotic drugs are used to treat bacterial diseases, and vaccines and bacterins are used to prevent viral diseases or bacterial infections.

4. Smearing method

It has the advantages of using less drug, being safe, and having small side effects, but its scope of application is limited. It is mainly used for treating a small number of cultured animals such as fish, frogs, and soft-shelled turtles, as well as body surface diseases of brood fish or animals whose bodies are injured after handling or long-distance transportation. It is suitable for skin ulcers and other local infections or trauma.

5. Hanging method

It is used for prevention before the season of epidemics arrives or in cases of mild disease. It has the advantages of using a small amount of drug, low cost, simplicity, and small toxic side effects, but it does not thoroughly kill pathogens. It can only play a certain role when fish and shrimp swim to the hanging bag feeding area to eat and move. At present, commonly used hanging drugs include chlorine-containing disinfectants, copper sulfate, and trichlorfon, etc.