Causes and prevention of death of river crabs when the weather is slightly cold, and how to catch young crabs?

The weather is a little cooler, which is the season when cultured river crabs mature and harvest, and it is also the time when river crabs are easy to die. Some crab farmers do not pay attention to strengthening management, resulting in a large number of crab deaths. Therefore, preventing the death of Eriocheir sinensis in autumn and winter is one of the keys to improve the survival rate of Eriocheir sinensis, and the following three aspects should be paid attention to:

1, natural death

As the saying goes, "When the west wind rises, the crab's feet itch." L 65438+ 10 Every September 1 day, a group of river crabs that have been growing for two years change from "yellow crabs" to "green crabs", and their gonads are mature and enter the final stage of their lives. Anyone who wants to escape with itchy feet will die naturally because of his maturity, increased osmotic pressure in his body and inability to adapt to the low osmotic pressure environment of fresh water. These crabs should be caught and sold in time when they are alive.

2. Died of a cold

When the weather is slightly cooler, the temperature difference between day and night is large, and the water temperature changes greatly, sometimes reaching l0℃. Eriocheir sinensis is very uncomfortable and easy to catch a cold, which leads to loss of appetite, difficulty breathing and death. Preventive measures are: pay attention to adjust the water level at ordinary times and control the drastic change of water temperature. When injecting fresh water, the temperature difference should not be greater than 3℃, and some cover plants such as water hyacinth and water peanut should be planted on the water surface. But not more than 1/2 of the water surface. When the weather changes, the water level will deepen.

3, indigestion death

Due to the change of air pressure and water temperature, the crab's appetite changes, which is easy to cause indigestion and death. This is what is usually called "bloating to death", and when it is serious, it will all die. Prevention and control measures: ① change the water quality and disinfect it regularly with lime water; ② Adding antibiotics and auxin to food regularly; 8 do not feed or feed less plant bait; ④ Feeding should be done regularly and quantitatively, and the feeding amount should be reduced appropriately when the water temperature drops.

Second, clever capture methods.

When the weather is slightly cold, two hailstorms are the peak season for river crab fishing. Adult crabs should be arrested and sold as soon as possible, and young crabs should be arrested and put in the pond. Because river crabs can live in the water, they can also go ashore and live in the ring.

When the environmental conditions change, they will dig holes to live, so fishing is more difficult. In order to catch adult crabs, people often use their breeding and migration habits to catch them in their migration channels. Compared with adult crabs, young crabs do not have this habit and it is more difficult to catch them. People have summarized the following fishing methods.

L, cage capture young crabs eat more vigorously because of the need to gain weight and shell? When the water temperature is suitable, they often look for food in shallow water and grass beside the pool. At this time, young crabs can be caught by setting cages, nets and other fishing gear, which are usually placed on the first night and caught the next morning. Because young crabs have the habit of not sleeping during the day and coming out at night, they often come out for food at night. It would be better to lure the river crabs by putting their favorite fish, animal offal and other feeds in the ground cage first.

2. Catching aquatic plants by net is an indispensable substance in the juvenile crab culture pond. Because the aquatic plants are tender and delicious, they can also play a role in shading the summer. Young crabs often inhabit here? When fishing, you can quickly copy it into the water with tools such as handwriting net, and then quickly pick it up with aquatic plants. Because the young crabs are agile, they dive immediately after making a sound and fall into the net bag to remove impurities. You can catch them one by one.

3. Trawl If the density of young crabs in the pool is high, trawl can be used. When fishing, you can drag the trawl back and forth along the edge of the pool. Young crabs will passively enter the net bag and can be caught after pulling out the net.

This method is often used in juvenile crab ponds after ponds are merged. When using it, be careful not to use it too many times, so as to prevent the mixed water from causing anoxia in the pond and the death of young crabs in the pond.

4. The pool water is drained by running water, and the young crabs often drill into manholes or dive into the bottom mud. At this time, you can use the habit of swimming against the current of young crabs, stimulate them with micro-flowing water, and catch them when they come out. The method is to form a small ditch in the middle of the pond, slowly enter the water on one side of the pond, and exit the water at the same speed on the other side. At the current, many young crabs often swim against the current and enter the ditch, which is very convenient to catch.

5. Build a nest to catch the habit of digging holes with young crabs. When grasping, you can consciously put obstacles such as bricks and tiles in advance. When the pool is drained, the young crabs will automatically get in. You can catch them by opening the bricks. In winter, after the water in the pool is drained, cover it with wet straw bags, water grass balls and agricultural films along the pool edge. Because of its warmth, young crabs will regard it as their own nest, and when they catch it, they can open these lids in order.

6. After digging a hole to catch the water in the pool and drain it, the young crabs often get into people's holes. If you find a crab hole, you can use a spatula to dig along the edge of the pool and dig to the bottom of the hole, that is, catch it.

7. Dry pool capture will quickly drain the pool water. Because the young crab can't make a hole and expose the bottom of the pool, it can be caught directly in the water. The crab in the pond can be completely and cleanly caught by comprehensively using the above methods for catching young crabs.