Crabs Eat Pests, Rice Provides the Environment: How to Raise River Crabs in Rice Paddies
Raising River Crabs in Rice Paddies
1. Apply fertilizer in moderation:River crabs cannot tolerate nutrient-rich water and are afraid of oxygen deprivation, so rice paddies used for crab farming should not be heavily top-dressed with fertilizer. Fertilization principle: base fertilizer is primary, top dressing is supplementary; generally, top dressing is applied once or twice during the entire rice growing period. For base fertilizer, apply 500 kg of manure, 30 kg of phosphate fertilizer and 10 kg of potassium fertilizer per mu; for top dressing, mainly use urea, 7-10 kg per mu each time.
2. Feed reasonably:For rice paddies used to rear young crabs, fertilize the water first and then release the seedlings. After the crab seedlings are put into the paddy, feed them 1—2 times a day with soybean milk or egg yolk, sprinkled evenly. After 1 week, gradually switch to paste-like bait, such as soybean cake paste, rapeseed cake paste, wheat bran paste, pumpkin paste, sweet potato paste, and paste made by simmering some chopped animal organs, and feed sufficient aquatic plants. During the molting period, add an appropriate amount of molting hormone to the bait. For fields used to rear adult crabs, around Qingming, for every 500 g of crab seed stocked, put in 50—110 kg of live river snails to let them spawn and reproduce on their own for the river crabs to eat, and appropriately supplement with some soaked or cooked plant bait such as wheat and corn. July-October is the peak growth period for river crabs, and the bait fed should be sufficient in quantity, comprehensive in nutrition and fresh. When crabs molt, add molting hormone to the bait, or appropriately feed some high-calcium bait such as eggshell powder, bone meal and shrimp shell powder. After October, the water temperature gradually drops, and the amount of bait can be appropriately reduced, generally 5%-10% of the crab's weight, fed in two portions: around 8 a.m., accounting for 40% of the daily bait amount, and the second feeding in the evening, accounting for 60% of the daily bait amount. Feeding should be done at fixed times, in fixed locations, with fixed quality and fixed quantity.
3. Prevent pesticide poisoning:Rice paddies used for crab farming should be sprayed with as little pesticide as possible. If pesticide must be used, choose highly effective and low-toxicity pesticides. When applying pesticide, choose a sunny morning, first drain the paddy water so that the crabs and fish gather in the ditches and sumps, then spray the pesticide, and try to spray it on the rice stems and leaves to reduce the amount of pesticide falling into the paddy soil and water. After using the pesticide, observe carefully; if any abnormality is found, immediately add water; if there is no abnormality, add water that evening.
4. Water quality regulation:The dissolved oxygen in the water of rice paddies used for crab farming generally needs to be above 5 mg/L, and the pH value is best at 7.5-8.5. When transplanting seedlings, use shallow-water transplanting, with a water level of about 20 cm, then gradually raise the water level to 60 cm as the water temperature rises and the seedlings grow. After May, change the water once every 7-15d. In hot seasons, change the water once every 2-3d, each time replacing 1/3 of the paddy water. When changing the water, note that the water temperature difference before and after the change should not exceed 3 degrees C, and avoid changing the water during the periods when river crabs are lurking and resting and at their best feeding time.
5. Disinfection and disease prevention:Before stocking, river crab seed should be bathed in a 0.2 mg/L malachite green solution. During the rearing period, every 7-10 d, splash 15-25 kg of quicklime per mu into the sumps and ditches once, and regularly mix oxytetracycline into the bait.