CATDOLL : CATDOLL: What kind of environment do hairy crabs like?

1. Temperature

River crabs are cold-blooded animals, and their body temperature changes with the change of water temperature. Changes in water temperature directly affect the predation, growth and metamorphosis of river crabs. When the water temperature is above 6℃, they begin to forage, and when it is above 15℃, they begin to molt and grow. 24℃-28℃ is the best water temperature for growth, and they are prone to precocious maturity when the water temperature exceeds 32℃ for a long time. Within the suitable temperature range, river crabs prey vigorously and grow fast when the temperature is high. Crabs are afraid of heat but not cold. If the water temperature is higher than 32℃, the molting of river crabs will be inhibited, but in winter, river crabs stop feeding and hide in caves to hibernate.

Crab breeding has certain temperature requirements. For river crabs to mate, the water temperature must be 8-12°C; during the egg-carrying crab breeding stage, the water temperature should be controlled at around 11-16°C; and for larvae to metamorphose, the water temperature must be 20-25°C.

Temperature changes have an impact on the growth and reproduction of river crabs. The temperature difference of water during the nursery stage should generally not exceed 2℃-3℃.

2. Salinity

River crabs have different requirements for salinity at different stages of their growth and development. River crabs like fresh water from the time they are megalopa larvae and migrate to fresh water to live. In autumn, when river crabs are sexually mature, they return to brackish water to mate, lay eggs and hatch. River crabs also have different requirements for salinity at each stage of their development. Crab seedlings usually need to be desalinated after they are grown, but mature enough crab seedlings do not need to be desalinated and can be directly placed in fresh water for breeding. Their survival rate can be as high as over 99%, which is higher than that of desalinated crab seedlings.

3. pH

In an overly alkaline or overly acidic environment, the tolerance of river crabs to hypoxia, the rate of molting and the rate of predation are all reduced, and the precipitation of calcium in the crab shell is affected. During the larval culture period, the pH value is generally required to be between 7.5-84, that is, neutral or slightly alkaline. If the water quality is acidic, it can be adjusted with an appropriate amount of quicklime.

4. Lighting

Light can promote the absorption of calcium by river crabs and promote the growth of their shells. In addition, light can promote photosynthesis of aquatic plants and increase the oxygen content of the water. River crabs prefer weak light and hide during the day and come out at night. They do not require high light during mating. The embryo is basically in a dark state in the early stage, but requires appropriate light in the later stage. In the larval stage, a certain light intensity is required, generally 2000-6000 lux. As the age of the larvae increases, the light intensity should also increase accordingly.

5. Oxygen

Crabs breathe by exchanging oxygen dissolved in water with carbon dioxide in their blood. Most of the dissolved oxygen in water comes from photosynthesis of phytoplankton. When the dissolved oxygen in water is above 5 mg/L, it is suitable for crabs to grow. When the dissolved oxygen in water is below 3 mg/L, crabs will float to shore and stop eating, which will inhibit the molting growth and metamorphosis of crabs.

6. Water plants

Water plants are the food and shelter of river crabs. They can photosynthesize to increase dissolved oxygen in the water, absorb and utilize excess nutrients in the water to purify the water, and serve as supports for river crabs to facilitate their movement. They can also prevent wind and waves and keep the water fresh. Therefore, there must be water plants in the waters where crabs are raised. River crabs are mainly raised with submerged plants, and can also be supplemented with a small amount of floating plants. Common water plants include: Elodea, Vallisneria, Hydrilla verticillata, Zizania lagenaria, Potamogeton, Water Peanut and Duckweed.

7. Water quality

River crabs like clean, pollution-free water with high dissolved oxygen. The water should not be too deep or too shallow. 0.6-1.2 is appropriate, depending on the season and temperature. The water should be deeper in summer when the temperature is high, and shallower during the Spring Festival when the temperature is low. Slightly flowing water is best.

8. Conch

It is generally believed that snails are a high-quality natural bait for river crabs, and it is advocated to feed them in large quantities. However, there are serious misunderstandings. First, feeding snails in large quantities consumes a lot of bait and oxygen during their growth and reproduction, which not only fails to improve the environment, but worsens it. Second, river crabs prey on snails, and often only eat a little bit, but most of it is wasted, and dead snails rot and pollute the water. Our company's experiments across the country have proved that as long as Jin Kangda river crab feed is fed, not feeding snails will not affect the quality, specifications and quality of river crabs, and it will also greatly save costs. However, the presence of a moderate amount of snails in the water naturally also has certain benefits.

9. Bottom

The bottom of the pond in the crab-raising water area is very important. Generally, hard bottom without silt is the best, because silt often contains a large amount of corrupt substances and pathogenic microorganisms, which are very easy to multiply in large quantities under suitable conditions, releasing toxic and harmful substances, polluting the water body and poisoning river crabs. Before stocking, dredging and drying the pond should be carried out every year. If there is no condition for dredging, the pond should be dried, the soil should be turned, and disinfected to neutralize and remove harmful substances at the bottom. During the breeding process, biological bottom modifiers should be sprinkled every 10-15 days to decompose rotten grass, leftover bait, animal carcasses, and toxic and harmful substances at the bottom.