Bigeye larvae serve as the foundation for crab breeding, and their quality directly affects the survival rate of young crabs from stage II to V. When purchasing bigeye larvae, it's essential to pay close attention to several key factors to ensure high-quality seedlings and successful cultivation.
Before buying bigeye larvae, farmers should familiarize themselves with the entire breeding process of the crab farm. This includes understanding the source of the broodstock, feeding practices, breeding cycles, and more. The broodstock used for producing seedlings should ideally come from natural lake environments, with males and females sourced from different water bodies. Female broodstock should weigh at least 125 grams, while males should be no less than 150 grams.
The quality of crabs raised using Artemia is generally superior to those raised on substitute feeds like freshwater quail or egg yolk. Additionally, the hatching period for bigeye larvae typically lasts 19 to 21 days, with an optimal emergence temperature around 21°C.
To ensure quality, proper identification of the larvae is crucial:
1. **Color**: High-quality bigeye larvae are light yellow, shiny, and transparent. Under a microscope, they should show no signs of microorganisms or filamentous bacteria.
2. **Body Condition**: Healthy larvae are robust, uniform in size, exhibit strong phototaxis, feed actively, have good swimming ability, and respond quickly to air blowing. When gently held in a small amount, they should clump together and disperse easily when released.
3. **Size Specifications**: Normal bigeye larvae should range between 120,000 to 140,000 per kilogram, with no more than 170,000 per kilogram. Crabs of this size tend to have fewer fake seedlings and transition smoothly into juvenile stages.
4. **Water Salinity and Temperature**: Upon emergence, the water salinity should not exceed 4‰, with desalination lasting at least 7 days. The water temperature should be around 21°C, and the temperature difference between the nursery pond and culture pond must be within 2°C, with a maximum of 4°C.
**Precautions to Take:**
1. Before releasing the larvae, it's recommended to disinfect them with appropriate drugs to eliminate pests and reduce disease risks. This also helps remove weaker individuals.
2. During harvesting, stop feeding and use light trapping methods. Drain the water before packing, ensuring even distribution in the containers.
3. Transport early-stage seedlings during the day and late-stage ones at night. Protect them from sun and wind during transit. When driving, keep windows closed, but open them for ventilation when parked. Spray water every two hours to maintain humidity inside the seedling boxes.
4. Before placing the crabs into the pond, allow them to acclimate gradually. First, open the container and spray water over the larvae for 5 minutes. Then submerge the box and larvae in pond water for a short time, let them sit on the shore for 15 minutes, repeat the process, and finally release them slowly into the pond.
By following these guidelines, farmers can significantly improve the success rate of crab cultivation and ensure healthy, vigorous seedlings for further growth.
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