Second-instar crabs like to live in fresh water (having a salinity of 0.5 or less), slightly alkaline (pH 7.5-8.5), and low ammonia nitrogen (0.2-0.5 mg/l total ammonia nitrogen). After a large number of feeding, the water quality is easy to be fat. In addition to planting aquatic plants, changing water frequently and maintaining a certain water level are indispensable. In winter and July to September, the average depth of pool water should be kept at the highest level (1.3 to 1.4 meters). From April to June and October to November, the depth of water should be 1 to 1.2 meters. In spring and autumn, the water is changed every 7~10 days, and the water exchange volume is 1/7~1/10 of the total water volume of the pond; in the summer, the water change is performed every 3~5 days, and the water change amount is 1/3~1/5. When water is used, the water temperature should not exceed 5°C, and the amount of water to be changed once should not exceed 1/2 of the total water in the pond. In case of the following conditions, the water should be flushed and changed in time:
(1) The food intake of hairy crabs was significantly reduced. During the day, the crabs went ashore without water, indicating that the pool water was deteriorating and the water should be flushed immediately.
(2) Continuous rain and sultry, oxygen consumption of organic matter is large, and water is not dissolved in water. It is necessary to flush and change water.
(3) If the weather is fine and it is not rainy, it is difficult to add water and splash lime water, 15 kg per mu. After adding water, the whole pool is splashed. In the main growing season of hairy crabs, it is usually splashed every 10 days to half a month.
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