Culture technology of swimming crab

Swimming crab, which is widely distributed along the coast of China, is a large marine economic crab with delicious meat, people like to eat and high economic value. Because of its fast growth, strong adaptability and less diseases, it is suitable for mariculture in coastal ponds, and it has become a new bright spot in coastal ponds in China in recent years.

Pond condition

1. The area and depth of the nurturance pond. Mainly to soil ponds, the area can be large or small, the water depth is required to be more than 1.5 meters. When the area of a single pond is more than 10 mu, it is appropriate to use a plastic net to separate the pond, so as to prevent the concentration of swimming crabs due to changes in water temperature and water quality, resulting in excessive local density and mutual cannibalism.

2. Bottom of the pool. Tilt slightly from one end of the intake gate to the other end of the drainage gate to facilitate intake and drainage. The bottom should be sandy and muddy, and there should be more corrugated ditches and ridges at the bottom of the pond, and hidden objects should be set up in the pond (such as waste pottery, stones, tiles, net clothing, bamboo, branches or using waste woven bags with appropriate amount of shells, etc.). As a hiding place for swimming crabs (especially during shelling). Note that the woven bags used must be cleaned. In the ponds with too much mud, about 10 cm thick medium and coarse sand can be spread on the bottom of the pond to provide a better living and growing environment for swimming crabs.

3. There is no pollution source around the culture pond, and the environment is safe.

4. Each flood season can naturally absorb the tide for about 10 days, and a lifting pump is provided to ensure the supply of aquaculture water during neap tide.

5. Configure appropriate amount of oxygen-increasing equipment.

Preparation before stocking

1. Clearing silt and eliminating damage

The silt in the pond was thoroughly removed a month before the seedling was released. Then use the disinfectants in the following table to remove enemy pests, predators and disease-causing organisms, and commonly use pond-clearing disinfectants:

Drug name use dose of quicklime 350mg / L ~ 400mg / L 7 days bleach (available chlorine ≥ 28%) seawater 40 mg / L ~ 50 mg / L 5 days fresh water 15 mg / L ~ 20 mg / L 5 days dichloroisocyanurate 5 mg / L ~ 10 mg / L trichloroisocyanuric acid 4 mg / L ~ 8 mg / L 10 days tea seed cake seawater 15 mg / L ~ 20 mg / L G / L for 7 days 60 mg / L ~ 90 mg / L for 7 days

2. Fertilizer and water

From 7 to 10 days before seedling release, after the toxicity of the disinfection drug disappeared, the water was filtered with a 60-mesh sieve net of 40 cm ~ 60 cm, and then 20 mg / L of nitrogen fertilizer or fermented organic fertilizer such as chicken manure was applied to cultivate the basic bait. make the pond water yellowish brown or yellowish green, transparent 30 cm ~ 35 cm. Or some shellfish such as clam, Sinonovacula constricta and other shellfish were put into mixed culture to facilitate the regulation of water quality and sediment or as live bait in the middle and later stages of culture.

Seedling stocking

1. Specification and quality of crab fry

Artificial crab seedlings were selected from Ⅱ stage to Ⅲ stage after molting for 1 ~ 2 days (dorsal nail length about 1.0cm). It requires neat specifications, strong individual, strong vitality, no disease and complete body appendages.

2. Crab seedling transportation

It is appropriate to use water transportation method: 0.8 meters × 0.4 meters plastic bags with 10 kilograms of water, rice straw or fluffy seaweed soaked in sea water or fluffy seaweed as concealment, in order to prevent juvenile crabs from huddling together. Each bag contains 50 ~ 100 grams of juvenile crabs, and the mouth of the bag is tightly fastened after being full of oxygen. It is required to be transported to the breeding pond within 10 hours as far as possible.

3. Intermediate cultivation and seedling release density.

The juvenile crabs from Ⅱ stage to Ⅲ stage should be cultivated in the middle, and then put into the breeding pond when the crabs grow to 3cm ~ 4cm in nail width.

The middle cultivation adopts an intermediate cultivation pond with the size of 1 mu ~ 3 mu, and it can also be cultivated in a small area of water in the middle of the big pond, which requires that the bottom of the pond can drain the pool water to facilitate harvest. It is also necessary to set up concealment or properly lay sand and cultivate good water color.

The intermediate cultivation density is 15 / m2 ~ 20 / m2, the water level of the pool is 70 cm ~ 80 cm, the transparency is about 30 cm, the dissolved oxygen is more than 5 mg / L, and the daily water exchange is 20% to 30%. The bait is mainly shellfish or small fish and shrimp, minced and fed 2-4 times a day. The feeding amount is 100%-200% of the crab weight, and it is better to eat it within 2 hours. At the same time, according to the crab molting, climate, feeding and other factors to make appropriate adjustments. After 10 ~ 15 days of cultivation, when the width of the carapace reaches 3 cm ~ 4 cm, it can be put into the cultivation pond.

Stocking density should be arranged reasonably according to seedling size, release time, pond size, number of hidden objects, bait condition, pond water quality and so on. In general, the stocking density of buckle crabs cultivated in the middle should be 2000 / mu ~ 2500 / mu, and if the juvenile crabs in Ⅱ ~ Ⅲ stage are raised directly, the stocking density should be 4000 / mu ~ 6000 / mu.

Culture management

1. Feed feeding

① feed species: low-value shellfish is the best, followed by low-value fresh miscellaneous fish and shrimp. Promote the use of formula feed to make up for the lack of natural feed, the content of crude protein in formula feed is required to be more than 35%, and the quality meets the requirements of GB13078 and NY5072. Before feeding live bait, the shellfish with thick shell should be mashed and the large fish and shrimp should be chopped. Pay attention to clean the fresh bait. When feeding non-shellfish bait, shell powder should be added to the bait if possible to prevent the swimming crab from growing slowly or shelling hard. After mating, Portunus trituberculatus should be fed with high-quality bait rich in protein and unsaturated fatty acids (such as sand silkworm) to promote the gonadal development of female crabs.

② feeding quantity: the daily feeding amount should be adjusted appropriately according to water temperature, water quality, weather, feeding condition, physiological condition, disease condition and other factors.

③ daily feeding times: usually twice a day, 70% of the total daily feeding in the evening and 30% of the total daily feeding in the morning.

④ feeding method: it is appropriate to feed evenly all over the pool to reduce the chance of swimming crabs gathering and kill each other. At the same time, the swimming crab in the shelling stage can be fed on the spot, and 3 ~ 5 bait tables are set up in each pond to check the food intake and residual bait.

2. Water quality management

① water quality requirements

The range of water temperature for water temperature growth is 12 ℃ ~ 32 ℃: the optimum water temperature range is 20 ℃ ~ 27 ℃, the temperature of stop drinking water is 8 ℃, the temperature of dormant water is 6 ℃, and the temperature of frozen water is 2 ℃.

Salinity growth salinity range 20 ‰ ~ 30 ‰: optimum salinity range 10 ‰ ~ 34 ‰

PH:7.8~8.5

Water color tea brown or yellowish green

Transparency 30 cm ~ 40 cm

Dissolved oxygen ≥ 4.0mg / L

Ammonia nitrogen ≤ 0.5mg / L

Hydrogen sulfide ≤ 0.1mg / L

② water quality control

When the crab seedlings were first released, the depth of the pond water was 40 cm ~ 60 cm. After releasing the crabs, water was added every 2 ~ 3 days, about 10 cm a day. After the pool water is added to 1.5 meters, it is necessary to change the water according to the water quality and color, combined with the application of fertilizers, microecological agents and water quality improvers to maintain the water quality requirements of Portunus trituberculatus.

In the case of high temperature and strong cold air, it is necessary to raise the water level in the pond, especially during the mating season from August to October, to maintain the highest water level and ensure the stability of the water environment, so as to facilitate the smooth mating of Portunus trituberculatus; in case of continuous rainstorm, it should be diluted in time and injected with fresh sea water to keep the salinity above 15 ‰ and strictly prevent the sudden drop of sea water salinity; in case of red tide, stop changing water.

If the PH value is too high, the PH value can be reduced by applying chelating copper, hypoalkaloid and other drugs; if the PH value is too low, quicklime 5 mg / L ~ 15 mg / L should be applied every half a month, which can not only stabilize the PH value of water body, but also provide calcium source.

In the hot season, especially in the muggy weather, the spoilage and decomposition of residual bait, feces and biological corpses will lead to hypoxia in swimming crabs, so it is necessary to turn on the ground oxygen machine to increase oxygen.

3. Male and female separate culture

When the crab body reaches about 100 grams, the male and the female can be distinguished. At this time, the male crab with the number of female crabs should be kept together with the male crab, and the rest of the male crab should be picked out and reared. After mating, the male crab should be caught and sold in time, so as not to affect the gonadal development of the female crab or the loss caused by the death of the male crab itself after mating.

4. Prevention and control of diseases

In the culture pond where the bottom of the pond deteriorates, due to bacterial infection or other biological parasitism, various lesions (such as abnormal black spots, shell perforation, etc.) will appear in the shell, abdominal limb, Gill and other parts of swimming crab, affecting the survival rate.

The main points for disease prevention and control are as follows:

① filters aquaculture water to prevent enemies from entering.

② regularly disinfects water with quicklime, bleach and chlorine dioxide to improve water quality and sediment.

③ maintains the stability of aquaculture water environment and prevents the stress reaction of swimming crab.

④ is fed with high-quality fresh bait, and appropriate anti-disease drugs are added to the diet during high temperature. It is recommended to use antibacterial and antiviral Chinese herbal medicine, such as allicin. Put an end to the use of highly toxic and high residual fishery drugs.

5. Daily management

① pond patrol: patrol the pond every morning, middle and evening to observe the changes of water quality, the activities of swimming crabs, the occurrence of diseases, as well as the safety of facilities such as gates and dams. Check the crab feeding and the quantity of residual bait 2 hours after each feeding in order to adjust the intake in time.

② water quality testing: daily measurement of water temperature, dissolved oxygen, pH, transparency, regular determination of salinity, chemical oxygen consumption, ammonia nitrogen and other water quality factors.

③ determination: the growth of crabs was measured every ten days, and the culture effect was measured by measuring nail length, nail width and body weight.

④ culture record: a culture log should be established for each pond, including clearing pond, seedling source, seedling specification, stocking quantity, release date, water quality control, feed source, feed type, feeding quantity, disease condition, type of drug, name of fishery drug, manufacturer of fishery medicine, dosage, quantity, mode, frequency, yield and sales destination, etc.

6. Harvest

① starting time: after separate breeding and fattening, male crabs can be harvested and listed in November, while female crabs mature gonads as late as mid-December, and ointment crabs can be listed according to the market situation. If you want to keep it for sale before and after the Spring Festival, you should raise the water level or use a plastic greenhouse to keep the water temperature above 2 ℃.

② start-up method

Drift net capture: release the net in the evening and close the net every 2 hours. It can be captured 4 ~ 5 times a night.

Crab cage capture: release the crab cage at night, collect the crab cage every 3 hours, and catch 3 times a night.

Net bag capture: fix the net bag at the gate of the sluice gate, use the low tide to release water, make the swimming crab enter the net bag with the water flow, and part of the swimming crab can be caught.

Dry pond capture: drain the pond water to the lowest place, rake slowly along the bottom of the pond with an iron rake, pick up the crab and pick it up with a hand-copied net.

Tie up the captured swimming crabs with rubber bands, rinse clean with sea water and put them into baskets, dry transport to market (at 2 ℃ ~ 4 ℃ temperature, swimming crabs dry dew for 24 hours, the survival rate can reach 90%).