Introduction to Common Drugs for Farmed Fish, Part Two

This article continues to introduce the commonly used disinfecting and sterilizing drugs bleaching powder concentrate, dichloroisocyanurate, trichloroisocyanurate and chlorine dioxide.

(2) Bleaching powder concentrate

[Properties] Bleaching powder concentrate is a white powder with a chlorine odor, easily soluble in water with a small amount of sediment. It contains few impurities. It is relatively stable and not easily decomposed by moisture. Its aqueous solution is alkaline. The active ingredient of bleaching powder concentrate is the same as that of bleaching powder, with available chlorine content reaching 60-65%, more than twice that of bleaching powder.

[Action] Bleaching powder concentrate is also a broad-spectrum disinfectant, with the same mechanism of action as bleaching powder. It also produces hypochlorous acid upon contact with water, and the unstable hypochlorous acid decomposes to release active chlorine and atomic oxygen, producing a sterilizing effect.

[Uses] The uses are the same as those of bleaching powder.

[Usage and Dosage] The available chlorine content of bleaching powder concentrate is generally calculated at 65%, and the commonly used amount for whole-pond splashing is 0.4-0.5 PPM. When used for disinfecting fish fry and tools, the dosage can be calculated by converting according to the available chlorine content with reference to the dosage of bleaching powder. For example, when using bleaching powder (containing 30% available chlorine) for fish fry medicated baths, the dosage is to make the water 10-20 PPM. When using bleaching powder concentrate (containing 65% available chlorine), the calculation is as follows:

Bleaching powder concentration used x bleaching powder available chlorine content / bleaching powder concentrate available chlorine content = bleaching powder concentrate concentration used. If the bleaching powder concentration used is 10-20 PPM. The specific calculation is as follows:

　　10PPM×30%÷65%=4.61PPM；20PPM×30%÷65%=9.23PPM

For medicated baths, the concentration of bleaching powder concentrate used is 4.6-9.2 PPM.

(3) Sodium dichloroisocyanurate

[Properties] Sodium dichloroisocyanurate (also known as "Youlüjing, Yukang") is a white crystalline powder with a chlorine odor, containing 60-64% available chlorine. Its chemical properties are stable; after being placed indoors for half a year, the available chlorine decreases by only 0.16%. It is easily soluble in water, and the aqueous solution is weakly acidic. However, its stability is poor. The prepared aqueous solution cannot be stored for long and should be prepared and used immediately.

[Action] Sodium dichloroisocyanurate is a broad-spectrum sterilizing and disinfecting agent with relatively strong sterilizing power. Its main disinfecting active substance is chlorinated uric acid, which decomposes into hypochlorous acid in water and has a strong oxidizing effect, easily acting on microorganisms and lower algal proteins, thus having a strong killing effect on bacterial vegetative forms, spores, viruses and fungal spores. It is commonly used to eliminate water pollution and prevent and treat various bacterial fish diseases in aquatic animals.

[Uses] Mainly used to prevent and treat bacterial diseases of fish such as gill rot, red skin disease, putrid skin disease and white head and white mouth disease; also used for disinfecting feeding grounds and tools and for pond clearing.

[Usage and Dosage]

1. Whole-pond splashing at 0.3-0.4 PPM can prevent and treat red skin disease and gill rot.

2. For feeding ground disinfection, sodium dichloroisocyanurate can be regularly splashed at the feeding ground. The dosage depends on the size of the feeding ground, water depth, water quality and water temperature. Generally, 100-120 grams is used, once every ten days. Splash the drug first, then feed the fish.

3. For pond clearing with water, use 10-15 grams of sodium dichloroisocyanurate per cubic meter of water. Fish can be stocked after 10 days.

4. For oral administration, the daily dosage is 60 grams per 100 kg of fish body weight (or 0.1 kg of sodium dichloroisocyanurate added to 10 kg of feed). Feed once a day for three consecutive days. It can be used to prevent and treat bacterial enteritis.

(4) Dichloroisocyanuric acid and LÜshaling

[Properties] Dichloroisocyanuric acid (also known as Fangsiaosan) is also a white crystalline powder, containing 60-64% available chlorine, with a slight chlorine odor and stable chemical properties. Its properties, action, uses, usage and dosage are similar to those of sodium dichloroisocyanurate (Youlüjing).

LÜshaling is a compound preparation with dichloroisocyanuric acid as the main drug. Its appearance and properties are similar to those of dichloroisocyanuric acid, and it contains about 60% available chlorine.

[Action] The action and sterilizing mechanism of dichloroisocyanuric acid are the same as those of sodium dichloroisocyanurate. Because Youlüjing is a compound preparation, the synergist added to it enables the aqueous solution of the drug to maintain a high concentration of "molecular hypochlorous acid" for a long time. This high-concentration hypochlorous acid is uncharged and has an extremely strong ability to penetrate bacteria, spores and viruses, 100 times that of hypochlorite ions. Therefore, the sterilizing effect of LÜshaling is higher than that of dichloroisocyanuric acid.

[Uses] Both dichloroisocyanuric acid and LÜshaling are commonly used drugs for preventing and treating bacterial diseases of aquatic animals. They are mostly used for fry and fingerling disinfection, tool disinfection, pond clearing, etc. LÜshaling also has the effect of deodorizing and purifying water quality.

[Usage and Dosage] The usage and dosage of dichloroisocyanuric acid and LÜshaling are the same as those of sodium dichloroisocyanurate. However, because dichloroisocyanuric acid is relatively irritating, it is not suitable for oral administration.

(5) Trichloroisocyanuric acid

[Properties] Trichloroisocyanuric acid, also known as strong chlorine essence, is a white crystalline powder containing 80-85% available chlorine, with a chlorine odor. Its chemical properties are stable. It is slightly soluble in water, and the aqueous solution is acidic. It decomposes upon contact with acid or alkali and is an extremely strong oxidizing agent and chlorinating agent. The greater the alkalinity of the water, the lower the efficacy of the drug, so applying quicklime affects the efficacy of trichloroisocyanuric acid. In addition, this drug cannot be mixed with phosphorus-containing drugs.

[Action] Trichloroisocyanuric acid is a highly effective, broad-spectrum, low-toxicity and safe disinfectant. It decomposes into cyanuric acid and hypochlorous acid in water and has a strong killing effect on bacteria, viruses, fungi and spores. At a concentration of 0.07-0.1 PPM, it can kill the myxobacteria and Aeromonas bacteria that cause fish diseases. [Uses] Commonly used for pond clearing and preventing and treating bacterial diseases such as gill rot, enteritis and red skin disease.

[Usage and Dosage] The maximum safe concentration of this drug is:

1. For pond clearing and disinfection with water, make the water 10-15 PPM; within one hour it can kill wild trash fish, shrimp, mussels, aquatic insects, etc. Fish can be stocked after 10 days.

2. To prevent and treat bacterial fish diseases, use whole-pond splashing. The amount used can be determined according to water temperature. Generally, when water temperature is <28°C, use 0.5 PPM; when water temperature is <28-30°C, use 0.4 PPM; when water temperature is <30°C, use 0.3 PPM.

3. Research on the pharmacological changes of trichloroisocyanuric acid after oral administration is still a blank, so it is better not to administer it orally. If it is used to treat skin diseases and there are no intestinal lesions, oral administration of trichloroisocyanuric acid, apart from stimulating appetite, is of no benefit to treatment.

(6) Chlorine dioxide

[Properties] Chlorine dioxide (ClO2) (also known as Baidujing, Sanjiu Yutai). Chlorine dioxide and its stabilized chlorine dioxide are both an oxidizing agent and a chlorine-containing preparation. Following the first-generation disinfectant bleaching powder, the second-generation disinfectant Youlüjing and the third-generation strong chlorine essence, it is called the fourth-generation disinfectant. It is a world-recognized A1-level broad-spectrum, safe and highly effective disinfectant confirmed by the World Health Organization. It is a new type of disinfectant currently used in aquaculture. It has been widely used in disease prevention and control in aquaculture. Chlorine dioxide contains 226% available chlorine, which is 9.2 times the chlorine content of bleaching powder at 25-32% and 4.2 times the chlorine content of dichloroisocyanuric acid at 60-64%. Chlorine dioxide is easily soluble in water; its solubility in water is 5 times that of chlorine, and it does not undergo hydrolysis after dissolving. Its disinfecting effect is not affected by the pH of the water quality.

[Action] Chlorine dioxide can effectively kill bacteria, viruses, fungi, bacterial spores and bacteriophages in water, and can oxidatively decompose botulinum toxin in water. In water, because the active ingredient molecules of chlorine dioxide have an adsorption effect with the viral capsid protein, a high concentration of disinfecting molecules accumulates on the surface of virus particles, thereby strengthening its killing effect. Chlorine dioxide can exert good sterilizing effects within the pH range of 6-10. In water at pH 8.5, its sterilization speed is more than 20 times faster than chlorine. Water bodies for greenhouse turtle culture often contain ammonia; using chlorine dioxide will neutralize ammonia and reduce the disinfecting effect, so it can make up for the weakness of ozone disinfection in not being able to remove ammonia. Chlorine dioxide has a particularly strong effect in removing phenol odor. More significantly, after using chlorine dioxide, the carcinogen 3,4-benzopyrene in water can be oxidized into a non-carcinogenic quinone structure.

The sterilizing ability of chlorine dioxide is stronger than that of chlorine, its sterilizing action is faster than that of chlorine, its duration of sterilizing effect is more than 10 times that of chlorine, and the drug effect of the residual dose also lasts longer. Experiments show that using 2.0 mg/L ClO2 for 30 min can kill almost 100% of microorganisms, while the remaining ClO2 concentration is still 0.9 mg/L. During application, it does not produce toxic side-effect substances such as organic chlorine, so it has no irritating effect on fish and shrimp and does not affect their feeding and normal development. It does not harm plankton, can improve water quality, deodorize and preserve freshness, and is a truly green disinfectant.

In addition, chlorine dioxide preparations at a concentration of 0.3 ppm-3 ppm can reduce the total number of bacteria in aquaculture water by more than 92%, and can increase dissolved oxygen in aquaculture water, with no obvious effect on inorganic nitrogen salts. A 0.3 ppm chlorine dioxide preparation has no obvious effect on phytoplankton, and below 1.2 ppm has no obvious effect on the zooplankton Daphnia in the water. 3 ppm can inhibit the reproduction and growth of phytoplankton, and a concentration above 2.4 ppm can affect the reproduction and survival of the zooplankton Daphnia. In terms of impact on water quality, chlorine dioxide preparations are also superior to other chlorine-containing disinfectants.

[Uses] Widely used for water quality treatment, disinfection and prevention and treatment of bacterial diseases in aquaculture.

[Usage and Dosage] Specific methods for using chlorine dioxide: Before using stabilized chlorine dioxide, it must undergo hydration treatment. Generally, citric acid is used as the activating agent. Chlorine dioxide and citric acid are dissolved separately at 1:1, then mixed and activated for 5-15 minutes before immediate use. If splashing over the whole pond, water can be continuously added for dilution and evenly splashed. It is mostly used for whole-pond splashing, using an amount that makes the pond water concentration 0.5-1 PPM.

Note: The medicinal solution cannot be prepared or stored in metal containers; do not place it together with acidic organic substances or flammable materials to prevent spontaneous combustion.