How to keep the aquatic plants at the mouth of river crab breeding ponds alive and play a positive role?
As the saying goes: "The size of the crab depends on the aquatic plants; the number of crabs depends on the aquatic plants." This sentence is believed to be cocooned by many farmers' ears, but it has been continuously verified in production practice. Aquatic plants play an indispensable role in the breeding of crustacean aquatic animals, and they also play an important role. The breeding of river crabs is even more dependent on aquatic plants. So what important role does aquatic plants play in the breeding process of river crabs? What are the common problems of crab pond aquatic plants that need to be solved?
1. The role of aquatic plants in crab ponds
The most common aquatic plants in river crab breeding ponds are Elodea and Hydrilla verticillata. Both of these two grasses have the characteristics of being fresh, tender, crisp and slippery. The stems and leaves of aquatic plants used in crab ponds contain a small amount of protein, fat, vitamins and other nutrients. In addition, the aquatic plants contain a certain amount of crude fiber, which can promote the digestion and absorption of a variety of foods by river crabs.
The range of activities of river crabs is not large, and it is impossible to stay in the water for a long time. Especially at night, river crabs will crawl or rest on water plants, so water plants have become a habitat for river crabs. When the river crab is shelled, the river crab is often attached to the aquatic plants. After the molting, the crab has a period of obvious weakness. At this time, the aquatic plants will provide a safe place for the crab to hide, which can effectively prevent the same kind of attack and other biological hazards , To ensure the safety of river crabs through the vulnerable period after shelling.
(1) Purify and regulate water quality
The breeding process of river crab has very high requirements on the aquaculture water environment. Planting high-quality aquatic plants in crab ponds has the function of regulating the water environment. The aquatic plants can release a large amount of oxygen under photosynthesis. At the same time, the aquatic plants can also absorb a large amount of harmful ammonia nitrogen subsalt, carbon dioxide and remaining feed dissolved substances and organic decomposition substances in the pond. .
(2) Other functions
In addition to these important effects on river crabs, aquatic plants have great benefits for the growth of zooplankton, phytoplankton, snails, etc. that exist in the water.
2. Frequently asked questions about crab pond aquatic plants
(1) Water plants do not grow up
In some culture ponds, after planting aquatic weeds or after disinfection, insecticide, and algae killing agents are used up during the breeding period, sometimes aquatic plants (such as Hydrilla verticillata, bitter grass, Elodea, etc.) stop growing and turn yellow. , Withering, rotten heads, rotten roots and other undesirable phenomena, leading to deterioration of water quality, reduced food intake or refusal to eat, and even large-scale disease.
(2) Turbid pond water
Many river crab farmers will face such an experience. They report that the water color of crabs has been white and muddy for a long time from one shell to two shells. No matter how fertilized and adjusted water, the water color will not improve. Long-term mixed water conditions make the water body unclean and prone to hypoxia. The growth of aquatic plants is stagnant or the roots are necrotic. It directly affects the growth of aquatic plants and crab production in the later period.
(3) Pests eat grass
After entering mid-to-late April, the water level in the crab pond has gradually deepened. At this time of the year, the pests are very serious. The larvae and red nematodes multiply in large numbers. They eat the planted aquatic plants in the pond, resulting in high temperature for planting. The grass cannot grow up, which affects the breeding of crabs in summer.
(4) PH is too high
In river crab breeding ponds, excessively high pH will inhibit the photosynthesis of aquatic plants and the decomposition of spoilage bacteria, slow down the decomposition rate of organic matter, slow down the material circulation process, and cause the reproduction of bacteria, algae, and plankton Affected, it will cause the death of phytoplankton in severe cases, make the water hypoxia, and cause the death of river crabs.
(5) Unsuccessful withdrawal of the shell
Crustacean aquatic organisms grow by molting, and each time the crab molts its shell weight will increase by about 20%. If the river crab cannot moult normally, not only will it fail to grow normally, but it will also die due to difficulty in moulting. In the process of breeding river crabs, the problem of death of river crabs due to unsuccessful molting is often encountered. In addition to the fact that this species of river crab is not adapted to the local water environment, it is also related to factors such as the nutrient composition of the feed, the pH of the water quality, the breeding conditions of the pond, and whether the crab species itself is sexually mature.
(6) Moss cyanobacteria outbreak
In recent years, many crab farmers have said that when the crabs are raised to the middle and late stages, cyanobacteria will burst out in the ponds. If the cyanobacteria are not handled properly, it will cause huge losses to the farmers' friends. The outbreak of cyanobacteria will increase the consumption of dissolved oxygen in the water body, which will lead to hypoxia during the growth of farmed animals and affect the normal growth of river crabs.
3. How to manage aquatic plants
(1) Controlling the coverage rate of aquatic plants
At the mouth of the intensive breeding pond for river crabs, the coverage area of aquatic plants generally needs to be maintained to account for 50%-60% of the entire pond area (that is, about 2/3 of the entire pond area), which is too large or too small. Affect the normal growth of river crabs, farmers can use manual cutting or mechanical cutting of the excess area. The old grass heads should be manually cut off the aquatic plants beyond the water surface, and try to control the grass heads 15-30 cm below the water surface, so that the aquatic plants can grow normally in the breeding pond and provide a good growth environment and shelter for river crabs.
(2) Control of aquatic plants in crab ponds
In the intensive breeding of river crabs, the cultivation of aquatic plants requires the combination of different types of aquatic plants to provide a thicker habitat for the river crabs more effectively. The deep water level at the ring ditch of the crab breeding pond can leave some Elodea. The middle shallow water platform should try to plant heat-resistant aquatic plants such as bitter grass to reduce the proportion of Elodea. Only by maintaining a reasonable collocation, water plants can make the best use of them.
(3) Adjust the water level appropriately
It was emphasized above that during the growth of aquatic plants, the grass heads beyond the water surface need to be cleaned up in time. In addition to manual cleaning, the position of grass heads in the water body can also be controlled by adjusting the water level of the pond. However, the water level of the crab breeding pond cannot be adjusted too high in a short period of time. If there is a short period of strong rainfall, the pond water will overflow, and the crab will also escape and cause losses.
(4) Proper oxygenation
Water plants in river crab breeding ponds consume carbon dioxide to produce oxygen through photosynthesis to ensure the balance of dissolved oxygen in the entire pond water environment. However, the balance of aquaculture water is disrupted, and the respiration of aquatic plants will be correspondingly weakened. Proper aeration and bottom improvement of aquaculture ponds can not only prevent the death of river crabs caused by hypoxia, but also ensure the respiration of aquatic plants and prevent the roots of aquatic plants from rotted.
Maintaining the vitality of the aquatic plants in the crab breeding pond during the high temperature season in summer can ensure that the crabs can still grow normally in the face of high temperature and other harsh environments. It is not an easy task. Farmers face a variety of complex problems in the daily management of aquatic plants. The daily management process of aquatic plants also tests the detail processing ability and perseverance of the farmers. It is not done overnight, but runs through the entire crab breeding process. I believe that doing a good job of daily management of aquatic plants, river crab breeding is not as difficult as imagined.
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