To improve the survival rate of fry stocking, it's essential to focus on two main areas: preparation before stocking and the actual stocking process. These steps are critical in ensuring a healthy environment for the fry and minimizing risks from predators or harmful substances.
First, proper preparation is crucial. Before introducing the fry, the fish pond must be thoroughly disinfected. There are two common methods: dry pond disinfection and water-based disinfection. For dry pond disinfection, after draining the pond, quicklime (75 grams per square meter) is evenly spread across the bottom. The pond is then left to dry under the sun for a few days, after which fresh water is added. This process should continue for about 4–5 days before the water is changed again, and the fry can be introduced after another 2–3 days. In the water-based method, 220 grams of lime per cubic meter of water is used. The lime is fully dissolved and spread throughout the pond. It's important to check for residual toxicity before releasing the fry. One way to do this is by testing the pH level—when it drops below 7, the toxicity has faded. Another method is to observe if there is still any visible presence of lime in the water. If not, it's safe to proceed.
Next, water quality should be enriched with fertilizer. About a week before stocking, the pond should be filled with 50–60 cm of water, and 250–300 kg of livestock manure water per mu is added to promote natural food sources like plankton. Additionally, pulling empty nets before stocking helps remove any wild fish, frog eggs, or aquatic insects that could harm the fry.
When it comes to stocking the fry themselves, careful selection and handling are vital. Fry should be healthy, disease-free, and at least 3 cm in size to reduce aggression among them. Before release, they should be soaked in a saltwater solution (1 kg salt in 30 kg water) for 5 minutes to prevent infections. The best time to stock is during peak rotifer activity, usually 5–7 days after fertilization, and preferably on sunny days when the water temperature is between 20°C and 25°C. Stocking density varies depending on the species; generally, 100,000 to 200,000 fry per mu is recommended, but this can be adjusted based on the type of fish. It's also important to avoid mixing different sizes or species to prevent competition and predation.
Before stocking, drug residues must be checked. A small number of fry can be placed in a cage in the pond to see if they survive for 12–24 hours. If so, the pond is safe. Also, checking the pH level is an effective way to confirm that the disinfectant has lost its toxicity.
Fry should be stocked into the pond when they are strong enough to swim actively, typically 4–5 days after hatching. Stocking too early may result in poor swimming ability, while waiting too long reduces survival rates. It’s best to raise one species at a time, using only fry from the same batch to avoid size differences and competition.
Stocking on sunny days is ideal, as the higher water temperature and dissolved oxygen levels help the fry adapt more easily. On cloudy or rainy days, the lower oxygen levels can stress the fish, leading to poor feeding and even death.
Applying manure to the pond before stocking is key to increasing the availability of natural food like rotifers. The concentration should reach 5,000–10,000 per liter. Base fertilizer should be applied 5 days prior, with 200–500 kg per acre, and chemical fertilizers can be added in smaller amounts for new ponds.
Before stocking, it's important to check the presence of zooplankton. Rotifers and nauplii are ideal, while larger zooplankton like copepods should be controlled using crystal solutions or fine mesh nets. All nets should be clean and free of disease before use.
Finally, when placing the fry into the pond, the temperature difference between the transport container and the pond should not exceed 3°C. Gradual acclimation ensures the fry adjust without shock. Careful placement is also important—fry should be released slowly into sheltered areas, avoiding windy conditions where they might be blown to the edges of the pond.
External fixation of the lower limb is a treatment used to fix a fracture or dislocation of the lower limb.The functions of these external fixation methods are mainly as follows.
1. Stabilize a fracture or joint dislocation.External fixators can fix the bone or joint in the correct position to prevent further displacement or dislocation,thereby promoting the healing of the fracture or joint dislocation.
2. Pain relief,external fixators can reduce pain and discomfort by fixing and supporting fractures or joint dislocations.
3. Promote fracture healing,external fixator can provide a stable environment,promote fracture healing and bone tissue regeneration.
4. Protect surrounding tissues.External fixators can protect surrounding soft tissues (such as muscles,tendons and blood vessels) from further damage and reduce the occurrence of complications.
In general,the classification and function of lower limb external fixation is mainly to stabilize and protect fractures or joint dislocation,promote healing and restore function.The specific treatment should be selected according to the patient's condition and the doctor's advice.