What are the pond-clearing methods? Remember these five before stocking fish fry

Before stocking fish fry, the aquaculture pond must be cleared to kill various predatory small wild trash fish, harmful aquatic animals and plants, parasite eggs, pathogenic bacteria, etc., creating a good environment for the growth of adult fish. The following five pond-clearing methods are introduced:

1. Clearing the pond with quicklime. When carrying out drainage pond clearing (that is, draining the pond water to a depth of 5-10 cm of remaining water before clearing), use 60-70 kg of quicklime per mu of pond; when clearing without draining, use 125-150 kg per mu of pond for every meter of water depth (200 ppm). When using quicklime to clear the pond, the quicklime must first be dissolved in water, and then immediately and evenly splashed over the pond.

2. Clearing the pond with bleaching powder. When clearing with drainage, use 4-5 kg per mu; when clearing without draining, use 12-15 kg per mu of pond for every meter of water depth (25 ppm). When using it, it must be dissolved in water and then splashed over the whole pond.

3. Clearing the pond with a mixture of quicklime and bleaching powder. When clearing with drainage, use 2-3 kg of bleaching powder and 30-40 kg of quicklime per mu of water surface; when clearing without draining, use 5-7 kg of bleaching powder and 60-75 kg of quicklime per mu of pond for every meter of water depth. The method of use may refer to the usage of quicklime and bleaching powder.

4. Clearing the pond with rotenone extract. When clearing without draining, use 1.3 kg per mu of pond for every meter of water depth (2 ppm). When using it, add water to dilute it 10-15 times and then evenly splash it over the whole pond.

5. Clearing the pond with croton. When clearing without draining, use 5-7.5 kg per mu of pond for every meter of water depth (9 ppm). Before use, the croton must be pounded and ground fine, put into a jar, then sealed and soaked in 3% salt water for 3-4 days; when using it, dilute it with water and splash it, together with the residue and water, over the whole pond.

Among the various agents above, quicklime has the best pond-clearing effect, as it can both eliminate pests and sterilize, and also loosen the bottom soil, improve the aeration conditions of the soil layer, and make the pond water fertile.

When using the above agents to clear the pond, the following matters must be noted: (1) Before use, check whether the agent is effective. (2) Clearing the pond is required about half a month before stocking fish fry. (3) The failure time of the above various agents is 5-10 days (about 5 days for bleaching powder, and 10 days for croton). To be safe, for fish ponds that have already been cleared with agents, a few fish may be test-stocked before stocking (commonly known as test fish); only after proving that the toxicity has indeed disappeared can fish fry be stocked in large quantities.