Key Technical Points on Drug Use in Eel Farming in Summer and Autumn

In the high-temperature seasons of summer and autumn, eel growth is at its most vigorous, but the incidence of eel diseases is also at its highest. Many farmers, when eels fall ill, “resort to desperate measures” and use drugs haphazardly, only to spend a lot of money in vain without curing the eel diseases. Worse still, drug abuse causes water quality pollution, and some eels do not die of disease but are poisoned to death by drug abuse. Therefore, scientifically selecting fish drugs is the key to effectively preventing and treating eel diseases.

Nowadays there are many kinds of drugs, and various new drugs emerge one after another. However, the principles of selecting drugs - high efficiency, rapid action, long-lasting effect, safety, low toxicity, few side effects, no residue, convenience and low price - represent the general trend in drug use. How should fishery drugs be correctly selected? How should fish drugs be reasonably used? The author offers a few humble opinions for everyone's reference:

1. Adhere to the policy of “comprehensive prevention, active treatment” and establish the concept of “prevention first, prevention more important than treatment.” Treatment is a measure adopted only when there is no alternative. Many fish diseases are difficult to cure, but prevention is very effective, such as eel saprolegniasis and ichthyophthiriasis. Even if these diseases are cured, the fish are ugly and deformed, making them difficult to sell.

2. In the prevention and treatment of eel diseases, try to choose high-efficiency, low-toxicity, low-residue fish drugs, and advocate the use of biological-source fishery drugs, biological products and Chinese herbal medicines. These drugs are safe, low in toxicity and residue-free, and have unique advantages in prevention and treatment.

3. When fish diseases occur, correct diagnosis should be made and the right drug should be used for the disease, to prevent abuse and blindly increasing the dosage, increasing the frequency of medication, or prolonging the medication time. Malachite green, pyrethroids and methamidophos are triple-effect pesticides (carcinogenic, teratogenic and mutagenic) and should be used with caution or banned. In particular, drugs and additives banned by the state must not be used.

4. In using drugs, avoid relying only on experience, disbelieving science, or blindly following others without having one's own judgment. Farmers value practical results and practice most, but they must not blindly copy others' experience. The specific conditions of every pond are different. Following others' lead like a cow's tail and applying drugs haphazardly means ignoring the differences in specific water conditions and fish conditions under different circumstances in actual drug use.

5. There must be correct methods of drug administration and a correct grasp of the timing of drug administration. Whether to use whole-pond splashing disinfection, medicated bathing, oral administration or smearing, the most effective method of administration should be chosen. Sometimes the drug should only be sprayed around the pond, and sometimes used on one side or in one corner of the pond, and attention should be paid to the choice. The timing of drug use must be appropriate: drugs cannot be used when fish are gasping at the surface in the morning, cannot be used on rainy or overcast days, and are not suitable at night when the water body is short of oxygen, operation is inconvenient and observation is difficult, and fish suffocation and poisoning accidents easily occur; drugs should not be used immediately after feeding.

6. Determine the correct dosage according to water conditions, fish conditions and weather. Too small a dose fails to achieve the treatment purpose, while too large a dose causes fish poisoning or even death. Eels have a certain sensitivity to drugs. Taking an eel pond with a water temperature of 22-30°C, a pH value of 7-8, and a water depth of 1 m per mu as an example: trichlorfon, appropriate amount 6-8 liang, maximum 1 jin; quicklime, appropriate amount 30-40 jin, maximum 60 jin; bleaching powder, appropriate amount 1.6-2.0 jin, maximum 2.5 jin; potassium permanganate, appropriate amount 2.5 jin, maximum 7-10 jin; fenvalerate, appropriate amount half a liang, maximum 1 liang. Only by mastering the lethal concentrations of these drugs can treatment measures be taken safely, reasonably and effectively.

7. Pay attention to drug incompatibility taboos and usage taboos. For example: trichlorfon, copper sulfate and bleaching powder must not be mixed with quicklime; table salt must not be mixed with quicklime or bleaching powder; two drugs that become turbid or precipitate when mixed must not be mixed; potassium permanganate can only be used in neutral water bodies, because if used in acidic or alkaline water bodies it will produce manganese dioxide precipitate, damage the gills of eels, and promote aggravation of gill rot or even death; Chinese and Western medicines should not be mixed; drugs sensitive to sunlight should be used away from light or in the evening to ensure efficacy.

8. Before edible fish are marketed, there should be a withdrawal period. This ensures that the drug residues in the marketed aquatic products meet the relevant requirements.