From mid-April, the second molting of river crabs began one after another. What are the reasons that affect the shelling of crabs?
First, the pH value rises sharply or fluctuates greatly.
Due to the changeable weather in April, it is easy to have a sharp rise or fluctuation in pH value. On the one hand, if the pH value is too high, most nutrients in the water may be absorbed by aquatic plants or mosses, and algae are scarce, so there are few nutrients available for crabs to absorb and utilize. At the same time, aquatic plants are too dense, which may lead to hypoxia in the middle of the night. After a long time, crabs will become weaker. On the other hand, if the pH value is too high, it will affect the eating quality of crabs, and they will go ashore in the grass in the middle of the night. In severe cases, there will be symptoms such as supporting claws and ring claws, and symptoms such as top shell and pulling feet will appear during the shelling period, which will reduce the success rate of crab shelling.
Second, the deterioration of sediments and excessive sub-salt.
It may be the reason for the excessive use of fertilizer in the early stage, especially the extensive use of farmyard manure and compound fertilizer in Bantian. Rainwater erosion may bring a lot of chemical fertilizer into the ring ditch of Bantian, causing nitrite to exceed the standard. If nitrite seriously exceeds the standard, it will easily lead to the phenomenon of river crabs going ashore and going to the grass in the middle of the night. In the molting stage, river crabs will pull their feet because of high nitrite content and insufficient dissolved oxygen in the water.
The deterioration of the bottom material causes a large number of anaerobic bacteria to multiply at the bottom, and the bottom is hot, which is easy to cause hypoxia at the bottom, which in turn leads to the increase of reducing substances such as sulfite and ammonia nitrogen at the bottom; It causes river crabs to go ashore to eat grass in the middle of the night, which affects the feeding and nutrient accumulation of river crabs.
Third, the climate is changeable.
There are many rainy days in April, and the temperature difference between day and night changes dramatically. The temperature difference between morning and evening is generally 5-7℃, and the maximum temperature difference even reaches 14℃. Due to the unstable climate, the crab's stress reaction leads to a serious physical decline, and it is difficult to shell.
Fourth, lack of nutrition.
Due to the continuous rainy weather, the temperature is low, the feeding conditions of river crabs are poor, the nutrient accumulation of river crabs is relatively insufficient, and the physique of river crabs is often weak. During molting, the top shell will pull its feet due to insufficient energy supply. Moreover, the interval between the first shell and the second shell is short, and a lot of energy is consumed in the process of molting the first shell. The second shell has already started before the crab's physique has recovered, so there will be a situation in which the second shell pulls its feet at the beginning.
5. Enemy invasion: crabs that are sick, injured and easy to shell.
Solution:
1, pay attention to the time of crab shelling, and it is expected that calcium supplement products will be sprinkled the day before shelling.
2. Pay attention to the weather conditions when shelling, such as temperature difference change in the morning and evening, sudden change of weather, rain and rainstorm, which are fatal to crabs.
3, dissolved oxygen, the amount of oxygen taken at night, many people have no concept of dissolved oxygen, you can imagine how long you can live without oxygen, crabs are the most vulnerable when they shell, so be sure to pay attention.
4, water plants, water plants are the habitat of crabs, we must do a good job of management, crabs in the shell, crabs are shelters. To avoid natural enemies.