A Complete Analysis of New Techniques for Clearing Ponds and Removing Wild Fish

Currently, the commonly used pond-clearing drugs in production include quicklime, tea seed cake, bleaching powder, bleaching essence, trichloroisocyanuric acid, etc.

1. Quicklime pond clearing. Quicklime (CaO) reacts with water to form strongly alkaline calcium hydroxide, causing the pond water pH (acidity and alkalinity) to rise sharply to 11-12, thereby killing wild miscellaneous fish, harmful organisms and various pathogens.

2. Tea seed cake pond clearing. Tea seed cake is a round cake pressed from the residue left after oil extraction from the seeds of the oil tea plant. Method of use: break the tea seed cake into small pieces, soak in water, and after soaking for one day and night at a water temperature of about 25°C it is ready for use. When applying, add more water and sprinkle evenly over the whole pond. For a pond with a water depth of 20 cm, the dosage per mu is 13 kg; for a water depth of 1 m, use 35-45 kg. The above dosage may be increased or decreased according to the species of wild miscellaneous fish in the pond. For fish that cannot burrow into the mud, the dosage may be smaller; otherwise, larger.

3. Pond clearing with bleaching powder, bleaching essence and trichloroisocyanuric acid. All of these decompose in water, releasing hypochlorous acid, which immediately releases nascent oxygen; it has a strong sterilizing and harmful-organism-killing effect. Bleaching powder usually contains about 30% available chlorine (this refers to the percentage of chlorine with disinfecting ability in the total amount), bleaching essence is pure hypochlorous acid with 60%-70% available chlorine, and trichloroisocyanuric acid contains 85%-90% available chlorine.

Method of use: first calculate the pond water volume. Bleaching powder is used at 20 g per cubic meter of water; the dosage of bleaching essence is 1/2 that of bleaching powder, while the dosage of trichloroisocyanuric acid is 1/3 that of bleaching powder. Dissolve them in water and immediately sprinkle over the whole pond. The key technical point of pond clearing with bleaching powder is that it must be prevented from absorbing moisture and deliquescing. Once bleaching powder deliquesces, its available chlorine content drops greatly, affecting the pond-clearing effect. Bleaching essence is relatively stable in nature, and trichloroisocyanuric acid is the most stable; if stored open for half a year, its loss of available chlorine is less than 10%. The "Water Body Disinfection Power" produced by Wuxi Huanuowei Animal Health Products Co., Ltd. uses drug synergism technology to maximize the release of trichloroisocyanuric acid activity, giving excellent pond-clearing and disinfection results.

When using the above drugs for pond clearing, generally 7-10 days must pass for the drug's effect to disappear before @#@234@#@ crab seedlings can be stocked. Bleaching powder-type drugs lose their effect relatively quickly; usually 5 days after pond clearing, shrimp and crab seedlings can be stocked.

The above several pond-clearing drugs each have advantages and disadvantages. Tea seed cake can kill fish, aquatic insects, frog eggs, tadpoles, snails, leeches, etc.; quicklime, bleaching powder, bleaching essence and trichloroisocyanuric acid, in addition to killing the above harmful organisms, can also kill aquatic plants, filamentous algae, parasites and pathogenic bacteria, etc., and their harmful-organism-clearing effect is rapid and thorough. Quicklime can also keep the pH in water stable, release nutrients such as nitrogen, phosphorus and potassium adsorbed by the mud, and improve water quality. It must be emphasized that for fish ponds in saline-alkali land, the pond water is highly alkaline and the pH is relatively high, so strongly alkaline quicklime should not be chosen as a pond-clearing drug; instead, bleaching powder-type drugs should be chosen. In addition, tea seed cake has a strong destructive effect on fish blood, while crustaceans such as crabs and shrimp are 50 times less sensitive to tea seed cake toxin than fish. Therefore, when tea seed cake is usually used for pond clearing, the drug dosage can only kill fish and other animals, but has no effect on shrimp and crabs, hence the saying that with tea seed cake pond clearing, the more crabs and shrimp are cleared, the more there are.

Given the introduction of the above several conventional pond-clearing drugs, several new techniques are specially provided for farmers with different culture targets for reference:

1. Bromoacetamide. This product is a white crystalline powder, easily soluble in water and ethanol, with a water solubility of 42 g at 25°C, and easily absorbs moisture. It is one of the drugs recommended by the World Health Organization, with a snail-killing concentration of 0.5-0.8 mg/L, a snail-killing mortality rate of 96.7%-100%, and a snail egg-killing concentration of 0.34 g/L.

Its impact on fish fry and fingerlings is far smaller than on snails and mussels. Under water temperature conditions of 18.5-26°C, the 72-hour LC50 for silver carp fry and carp fry is 9.4-9.8 mg/L, and for grass carp fry it is 9.5-11.3 mg/L. At the general application concentration of 6 mg/L, fish are safe and sound. Fish and shrimp can be stocked after 10 days. This product has been trial-used on a large scale in Pengze, Tianfeng, Xifeng in Jiangxi and in Anhui, Fujian and other areas.

2. Niclosamide. It is a good snail-killing drug approved by the World Health Organization. Because it is itself insoluble in water, it is made into an ethanolamine salt so that it can dissolve in water. A snail-killing concentration of 0.3 mg/L can cause death, and it can also be used to kill adult tapeworms. In order to strengthen the effect of this agent, if this agent is compounded with rotenone powder, it can completely kill snails, fish and shrimp, and fish can be stocked after 15 days of use.

3. Rotenone. This product is available as a 7.5% powder and 2.5% and 7% emulsifiable concentrates. Its application rate is 0.3-0.4 mg/L, and it can kill fish fry and fingerlings, but it should be avoided during the molting period of shrimp and crabs to avoid causing death.

4. Cartap, also known as Padan, is obtained by artificial synthesis using biological nereistoxin, etc. The product is a 98% soluble powder. A dosage of 0.15-0.21 mg/L can kill snails, and 0.25-0.3 mg/L can kill domestic fish fingerlings. In killing fish, the general pattern is that large fish die first and small fish die later. During the period of use, water cannot be changed or added, otherwise they will revive and survive.

Wuxi Huanuowei Animal Health Products Co., Ltd. combines the above several techniques and uses compounding technology to produce an environmentally friendly pond-clearing agent, "Qingtangling." On the one hand, it can serve as a pond-clearing agent before shrimp and crab culture, and can also kill fish during the culture process; on the other hand, it can also promote shrimp and crab molting and stimulate the growth of shrimp and crabs. During use, each place should increase or decrease the dosage accordingly according to actual culture conditions.