Crabs can only grow when they molt, which is a critical stage in their development. For successful molting, crabs must be placed in an appropriate environment that meets specific ecological conditions. These include shallow water, low light levels, a quiet setting, clean and fresh water, and a variety of high-quality, palatable food sources. If these requirements are not met, crabs may fail to molt or even die during the process. During the molting period, several important factors should be carefully monitored:
First, observe the crab’s body color and feeding behavior. Before molting, crabs typically have a darker coloration—yellow-brown or dark brown—with hard legs and a rust-colored (brown) plastron. After molting, their body color becomes lighter, the plastron turns white, and their legs become soft. Crabs usually stop eating before they begin to molt. If you notice that after feeding, more larvae remain uneaten, or if the crabs are gathering near the shallow edges of the pond, it could indicate that molting is about to start. The presence of empty shells is a clear sign that many crabs are beginning to molt.
Second, to ensure asynchrony in molting, it's essential to provide high-quality feed containing minced meat before each large-scale molting event. Increase the proportion of animal-based food in the total diet to over 50%, ensuring that the food remains palatable and abundant. This helps prevent crabs from preying on soft-shell crabs, which can lead to losses.
Third, increase the calcium content in the water. Once molting begins, you can add lime (with caution during hot weather) to the water. Apply approximately 7.5 to 10 kg of lime per acre to disinfect the water and boost calcium levels, which supports shell formation. Additionally, you can sprinkle calcium dihydrogen phosphate at a rate of 0.75 to 1 kg per acre.
Maintain a stable water level. Before molting, it’s beneficial to flush or change the water to stimulate the process. However, once crabs enter the active molting phase, keep the water level steady and avoid frequent changes.
Finally, strengthen daily management practices. Regularly remove floating debris and decaying aquatic plants. Adjust feeding amounts appropriately during molting, and strictly avoid feeding in areas where many crabs are molting. If soft-shell crabs are found during inspections, they should be protected immediately. They can be collected and placed in buckets for 2 to 3 hours until they regain mobility, then returned to their original location to minimize stress and improve survival rates.
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