How to breed cream crabs?

Scyllaserrata (scientific name: Scylla serrata) belongs to crustacea, Portunus (Polypodiaceae). I like to make holes in the shallow sea near the shore and the sediment bed in the estuary. It is fierce and carnivorous, and its staple food is fish, shrimp and shellfish. The meat is delicious and nutritious, and has the effects of nourishing and strengthening the body. Especially pregnant female crabs produce red or yellow paste in their bodies, which is called "cream crab" and "sea cucumber" in southern China. Rich in warm shallow seas, mainly distributed in China coastal areas, Zhejiang, Guangdong, Guangxi, Fujian and Taiwan Province provinces, especially in Jiangsu and Zhejiang provinces. Nutritional Analysis The blue crab is rich in protein and trace elements, which has a good nourishing effect on the body.

breeding technology

First of all, the aquaculture pond

It is best to have a rectangular crab pond with an area of 333- 1000 square meters. The wall of the pond is made of slate or brick, and the height is about 1 m. The walls of the pond are generally fenced to prevent escape, and the bottom of the pond is paved with coarse sand or gravel. It is best to lay the slate first, and the slate is close to each other without leaving gaps, and then lay sand on the slate, with a height of about 10 cm.

Second, stocking.

Before stocking the blue crabs, clean the wall and bottom of the pond, disinfect with potassium permanganate or sodium hypochlorite, and then rinse with fresh water. The cultured blue crab requires complete limbs, strong and disease-free, no trauma, strong vitality, clean body surface and weight above100g. The amount of stocking depends on the size of the individual. General individual weight 100-500g, stocking capacity 1000-2000/ mu. Fattening crabs and strong yellow crabs should be stocked separately, and the blue crabs should be soaked in formalin solution of 100- 150ml/m3 for 30-60min.

Third, feeding management.

(1) Feeding and feeding blue crabs like to eat shellfish and small crustaceans, and sometimes they also eat some plant bait. Cultured meat crabs and blue crabs are alternately fed with live low-value shellfish such as green clams, muscle clams, short-toothed clams and snails, snails, fresh shrimps, small fish and artificial compound feed. In addition to feeding low-value shellfish and shrimp, Zhuang Yellow Crab should also be fed with high-protein and high-energy bait such as oyster meat, nereis and starworm, so as to meet the needs of Zhuang Yellow to promote maturity and accumulate energy. The blue crabs are usually fed in the evening and early morning, usually once in the evening, and the daily feeding amount of live shellfish is 15%-20% of the weight of the blue crabs. 4%-6% of fresh shellfish, nereis, small fish and shrimps, and 2%-4% of special compound bait for blue crabs, subject to no surplus the next day.

(2) Water quality management in the breeding period requires changing water at least once, and the water exchange rate is 100%. Before and after changing water, the water temperature and salinity should remain basically stable. When changing water, it is necessary to clean up the pollutants such as the excrement of children and blue crabs left at the bottom of the pool and rinse them with clean water. Keep continuous aeration and thin water convection for 24 hours, with a panoramic view of daily flow 1-2, and constantly monitor water temperature, salinity and PH value to maintain good water quality and geology.

(3) Daily management: regularly monitor the water quality, closely observe the active feeding situation of the blue crab, adjust the feeding amount in time, and take measures to deal with problems in time. Feed the bait regularly every day, drain water on time, remove the residue in the tank and other dirt at the bottom of the pond, ensure that the water quality of the pond is fresh, the pond and the bottom are clean, and the dissolved oxygen is sufficient to create a good breeding environment. Regularly bathe the cultured blue crabs, clean and disinfect the breeding environment and tools, and do a good job in disease prevention and control of blue crabs.

Pond preparation

Polyculture of blue crab in pond refers to the cultivation of other economic biological species in the pond where blue crab is cultivated, forming a mutually beneficial diversified aquaculture ecological structure, including crab-fish polyculture, crab-shrimp polyculture, crab-shellfish polyculture, crab-algae polyculture, etc., which can be single polyculture or multiple polyculture. The following mainly introduces several common techniques of mixed culture of blue crabs in ponds for farmers' reference.

1, polyculture variety

Practice has proved that the fish mixed with Scylla serrata mainly include tilapia, mullet, Osaka crucian carp, blind fish, spotted sole and so on. This is because mullet, blind fish, tilapia and other fish mainly feed on benthic diatoms, phytoplankton and organic debris. Under the condition of proper stocking, they will not compete with Scylla serrata for food, but also make the composition of the food chain in the crab pond more perfect, effectively use the natural bait organisms and corrupt organic matter in the pond, play the role of "scavenger", and reduce the deterioration of water quality caused by the residual bait of Scylla serrata. The adaptability of these fish to salinity and temperature is similar to that of Scylla serrata, and they can be caught at the same time. Snakehead has strong swimming ability, which can increase the exchange between the upper and lower layers of pool water and make more oxygen in the air dissolve into the pool. As long as the stocking time, specifications and density of fry are well mastered, the survival rate and yield of Scylla serrata will not be affected, and the income of fish farming can be increased.

In the coastal areas of Zhejiang, Fujian and Guangdong provinces, mullet and tilapia are mostly mixed with Scylla serrata. In crab culture areas with salinity below 8‰, crucian carp or Osaka crucian carp can be mixed, and the purpose of purifying water quality and increasing income can also be achieved.

2. Pond conditions

Generally, Scylla serrata ponds can be mixed with fish, but ponds with an area of about 10 mu, a water depth of more than 1.5m and a water depth of less than 1m are not suitable for mixed culture of fish. Because the water is too shallow, the floating mud at the bottom of the pond turns up, and the water quality becomes turbid, which affects the breathing of fish and crabs. The bottom of the pond should be muddy, because it is easy to grow a large number of benthic diatoms on its surface, commonly known as "oily sludge", which is the main food of mullet and tilapia. The bottom of the pond is slightly inclined to the drain, and a fish chute of 10 ~ 20 square meters is built at the drain. The fish tank connects all ditches, which is about 40 cm lower than the bottom of the pond, which is convenient for centralized fishing when the pond is dry. The water quality indexes of crab polyculture pond are: salinity 8 ‰ ~ 30 ‰, pH 7.8 ~ 9.0, dissolved oxygen more than 5 mg/L [2].

3. Preparation before stocking

Clean the pool with bleach, quicklime, etc. After the toxicity of drugs in the pool is eliminated, the raw water is released and then enters the new water. After 40 ~ 60 cm of water, the bait organism can be fertilized and cultured, and then gradually deepened. Apply organic fertilizer such as chicken manure or pig manure 100 ~ 150 kg per mu after entering the water. 5 ~ 10 days after fertilization, plankton in the pond proliferated in large quantities for the stocked fry to eat.

Seed selection transportation

The source of fry cultured by blue crab is artificial seedling raising; The second is to catch big-eyed larvae (crab seedlings) in the sea area; The third is to capture natural crab species. Artificial seedling raising is neat and pure, and it is still in the experimental stage, and the large-scale productive seedling raising technology has not been completely broken. Before the breakthrough of artificial culture technology, catching crab seedlings and crab species in natural waters is still the main source of artificial culture of blue crab.

1, catch big-eyed larvae

(1) Crab fry fishing. Blue crabs lay eggs in high salinity waters. After hatching, the larvae metamorphosed into megalopa, and then gradually moved to estuaries and inner bays, living in a slightly lower salinity environment. This is the season of sowing. Natural crab fry can be caught in the coastal areas of Zhejiang from April to165438+10, and the peak seasons are May to June and August to September. Crab fry fishing methods mostly use fixed nets, push nets and hand-copied nets. All localities should choose according to local conditions according to the specific situation of tide and wind and waves.

(2) Identification of crab seedlings. In the captured natural crab larvae, there are often big-eyed larvae mixed with other crabs, which need to be identified and selected.

(3) Cultivation of young crabs. Juvenile crab cultivation refers to the process of intensive cultivation of crab seedlings caught in natural sea areas or artificially cultivated young crabs. After cultivation, the young crabs are bigger, stronger in resistance and higher in survival rate.

2. Catch natural young crabs

Natural young crabs come in different sizes, and it is required that the young crabs caught should have strong physique, complete appendages, no mechanical damage and few attachments. Young crabs along the coast of Zhejiang Province are concentrated in the middle of June-July (also known as summer crabs and plum crabs) and from the middle of September to the early and middle of1October (known as autumn crabs). The commodity specifications of summer crabs can be made directly in that year, and the commodity specifications of autumn crabs can only be made after wintering. The exposure time of blue crabs after fishing should be short, especially in hot and humid summer. Generally, when the temperature is above 28℃, it will not exceed half a day, and when it is below 25℃, it will not exceed 2 days. The shorter the time from capture to stocking, the better. Too long will cause death.

Identification and selection of seedling quality of Eriocheir sinensis.

Crab fry caught and autotrophic in the local sea area generally have a high survival rate because of basically the same environmental conditions and short exposure time. For example, crabs transported for a long distance must be strictly selected, and sick crabs can only be released. The methods of seedling selection and identification are as follows:

(1) Choose healthy crabs. The shell of healthy young crabs is turquoise, complete and intact, with sensitive sensory response and strong activity, which is difficult to catch; Swimming feet and claw feet should not be missing and disabled, and the number of feet should not exceed three. If one foot is broken or injured, the remaining limb can be broken at the joint between the base joint and the base joint, and the new appendage will regenerate in a short time. If not removed, the residual limb will lose a lot of body fluids, leading to death. Crab seedlings of different colors (such as dark blue, reddish brown, rust color, etc.). ) on the shell, the abdomen and appendages are of poor quality, so it is best not to choose them.

(2) no disease. Distinguishing a sick crab can be judged by the color of the muscles at the foot root. The flesh is blue and purple, and the muscles of the limbs are not sunken. The elastic ones are healthy seedlings. If the muscles are yellow-red or have white spots, and the muscles between the limbs are depressed and inelastic, it is not suitable for breeding.

(3) Eliminate the crab slaves. There are a few 1 or more crab larvae at the base of abdominal segment. The crab slave is oval in shape and soft in constitution. It absorbs nutrition from the blue crab to maintain its life. Normal growth and development are affected by parasitic blue crabs, so crab slaves should be eliminated in time when selecting.

Three crab seedlings transportation.

Young crabs are usually transported by hard reeds or wooden boxes. Spread a layer of wet grass at the bottom, put a layer of crabs on it, and then cover it with a layer of wet grass to prevent the young crabs from being injured. Don't overlap too much, and finally cover it with a hard frame screen, which is convenient for seawater to shower on the way and improve the survival rate of transportation.

Seedling stocking

The stocking time of mixed fish culture varies with species and regions, and can be determined according to specific conditions. Crab fry stocking is carried out after fry stocking. Generally speaking, when the mullet fry is more than 3 cm, the blind fish fry is 3 ~ 6 cm, and the tilapia fry is about 6 cm, the Scylla serrata fry can be put into polyculture. If you put crab seedlings first, you should put bigger fish species.

In mixed culture, the stocking density of crab seedlings is basically the same as that in a single culture pond of Scylla serrata, that is, about 30 grams per mu of Scylla serrata seedlings 1500 ~ 2000. Under the condition of ensuring the output of Scylla serrata, put 100 ~ 200 mullet fry or about 200 blind fry per mu. Tilapia can reproduce naturally in the pond, and the number of fry should be controlled, and the stocking density should be 0/00 per mu/kloc. If the parthenogenetic male tilapia can be put into the pond, it will not reproduce and the stocking density can be increased appropriately. When Scylla serrata is mixed with mullet, tilapia and white shrimp, 60-80 mullet, 30-40 tilapia and 2000 white shrimp can be raised per mu.

Cultivation management

When the Scylla serrata has enough bait, it is not necessary to feed mixed bait. If the bait of Scylla serrata is not enough, bean cake, rice bran, bran and fish are mixed with bait. It can be added as appropriate, and the amount of bait should be such that the fish can finish eating within 1 hour. Feed it twice a day in the morning and afternoon, and after feeding the bait for about 1 hour, feed the Scylla serrata bait to reduce the competition for food and improve the utilization rate of bait.

Daily management work mainly includes adding and changing water, patrolling the pool, controlling water color, preventing diseases, escaping, floating head, preventing diseases and preventing theft. [3]

Closed culture

Scylla serrata likes to live on mudian bottomland in intertidal zone, moving at night and living in caves or hidden objects during the day. In winter and spring, when the water temperature is low, people usually dig holes to live. The temperature and salinity are wide, and the breeding seasons vary from place to place. From May to July, a large number of summer seedlings appeared along the coast of Zhejiang. Under the condition of artificial cultivation, after 2 ~ 3 months of cultivation, the individual specifications of summer seedlings can reach more than 200 ~ 250 grams.

Breeding facilities

Aoi, bay or high tide area supported by pond dam should be selected, and the monthly natural water inflow should be above 10 days. The buried area of aquaculture should not exceed 20 mu. The dam is made of mud or stone, with a width of more than 0.5m and a height of 0.6 ~1m. Spring water can overflow the dam, freely enter and leave the Cultural Dam, and often store water (including the inner ring ditch of the dam) 1.5m or more ... The dam is enclosed and blocked, with more than 9 strands of polyethylene wires, and the mesh 1 ~ 2cm, and the blocking height should exceed the highest tide level in the local history by 0.5 ~1m. Add an inverted net with a width of 40 cm to the upper end of the block. In order to prevent the blue crab from escaping over the net, the net is folded inward and forms an included angle of 45 ~ 60 with the pulley. The lower end of the block is buried at the bottom of the dam. In order to prevent rats from biting the net, the block base can adopt a double-layer structure. Bamboo inserted into the supporting guardrail should be selected with a diameter greater than 10 cm, and the spacing should not be greater than 2m. Together with the lower end of the barrier, the dam should be inserted under the dam foundation, and the bamboo should be reinforced with climbing ropes inside and outside. According to the size of the aquaculture dike, the water inlet and outlet gates should be set, but the sewage screens should be built inside and outside the gates accordingly. Excavate a ring ditch or a central ditch with a depth of more than 0.8m in the breeding embankment, and the area of the ditch accounts for more than l0% of the area of the breeding embankment. Hidden objects such as cylindrical tiles are set on the surface of the city wall for the blue crabs to inhabit.

Seedling stocking

Young crabs develop and utilize the overwintering seedlings of last year or the summer seedlings of that year. Seedlings should be intact, swimming feet and claw feet should not be missing or damaged, at most, four feet should not be missing, and there is no disease. Soft-shelled crabs are not suitable for breeding. Artificial fattening utilizes fertilized female crabs or lean male crabs. Stocking density depends on water quality, feed and other conditions. Generally, young crabs are stocked at 3000 ~ 5000 per mu, and the specifications of fattening seedlings are large, and the stocking density can be controlled at 2000 ~ 3000 per mu. Where conditions permit, it is best to separate the size and specifications, and separate the males and females.

Feeding and management

Blue crabs are mainly carnivores and like to eat shellfish, crustaceans and fish. Feed needs to be fresh. The daily feeding amount is 20 ~ 10% of the weight of the blue crab pond (according to the standard of small miscellaneous fish), which can be gradually reduced to 10 ~ 5% with the poor growth of individuals. Feed twice a day, and the feed should be evenly scattered around the pool. Don't throw it into the ditch. According to the change of environmental conditions, how much bait to master; Less investment in small flood season, more investment in large flood season; Less investment in hot and muggy weather, poor water quality, no investment when floating head; If there is too much rain, feed less when the pool water is turbid, and stop feeding when the water temperature drops below 5℃. The water quality management of cage culture is convenient, because the tide can freely enter and exit, and the water quality conditions are good, but the water depth in the dike (including the dike) should always be above 1.5 meters. During the period when the tide can't enter the pond, a pump should be set to pump water. Generally, the water should be changed every 3 days 1 time. It is very important to check the pond every day, especially before the dam is submerged by the tide. It is necessary to carefully check the trash screen (especially the bottom of the screen), the dam and the gate, and repair the damage and leakage immediately if found. In order to prevent and kill pests, such as goby, catfish and so on. We can choose that the weather is cool every half month to 1 month in the flood season, and drain the pool water to catch pests, but the tide should be accurate, so that the water can quickly enter the pool after the end and avoid long-term drying of the pool.

catch

Or take the method of alternating grasping and releasing, grasping fat and keeping thin, or grasping at one time. Generally, when the water temperature drops below 13℃ in autumn, the vitality of the blue crab is weakened, so it should be caught in time. After harvesting in autumn, the autumn seedlings of that year can be released immediately, and kept for the next year after wintering. 1 year can be artificially fattened for many times.

5 disease and prevention

1. Bacterial diseases [4]

1. 1 Vibrio is a bacterial disease.

Vibrio bacteria (such as Vibrio anguillarum and Vibrio parahaemolyticus) can cause diseases of hemolymph and other organs of aquatic animals such as fish, shellfish and crustaceans, and cause huge economic losses to aquaculture. Mao Zhijuan and others reported that pathogenic vibrios such as Vibrio cincinnati, Vibrio alginolyticus and Vibrio parahaemolyticus were isolated from the pleural fluid of sick Scylla serrata.

1.2 crustacean ulcer

Crustal ulcers are mainly caused by bacteria that degrade crustaceans, such as Aeromonas, Flavobacterium, Pasteurella, Vibrio and so on. These bacteria mainly degrade the exoskeleton of crustaceans, causing crustacean-degrading bacteria and fungi to infect the epidermis of crustaceans, leading to crustacean ulcer and erosion.

1.2 Fungal diseases

The fungal diseases of Scylla serrata are mainly fungal diseases, such as Streptomyces, Schizochytrium and Schizochytrium, which can cause crab diseases. The larvae of Scylla serrata with fungal diseases usually have poor phototaxis and decreased vitality, and most of them are free in the middle or lower layer or the bottom of the water layer. The development of the egg body is blocked and it cannot hatch.

1.3 Viral diseases

Viruses that cause the disease of Scylla serrata mainly include reovirus, herpes virus and white spot syndrome virus.

1.4 Parasitic diseases

The common parasites that parasitize Scylla serrata are crab slaves, barnacles, gill worms, sea otters and so on. Once the parasite entered the crab, it began to multiply in large numbers, infecting gill cavity, abdomen, muscles and other tissues and organs, and eventually leading to the death of the blue crab.

Traditional prevention and control measures focus on prevention, supplemented by treatment, mainly in the following aspects. (1) Do a good job of disinfection and regular dredging of the whole pond before stocking. (2) Change the water in time. (3) Strengthen manual management: do a good job in the selection, stocking, daily feeding and management of crab seedlings to reduce the occurrence of diseases of Scylla serrata. (4) Garlicin is regularly sprinkled in the culture pond to kill pathogenic microorganisms in the water and prevent bacterial diseases and parasitic diseases.

2. 1 Breeding of new disease-resistant varieties

Cultivating new varieties with strong disease resistance is one of the important measures to prevent diseases of Scylla serrata. The cultivation of new varieties can improve the germplasm characteristics of crabs and enhance their disease resistance. Commonly used variety improvement techniques mainly include: (1) breeding new crab varieties with disease resistance through distant hybridization. (2) Transgenic technology can express the stress resistance genes of crab species and improve their disease resistance. (3) Polyploid culture technology can improve the survival rate of river crab culture and reduce the occurrence of diseases.

2.2 the use of biological agents

The innate specific immune mechanism of Scylla serrata is not perfect, and it is easy to be invaded by some pathogenic microorganisms. Traditional drugs (such as oxytetracycline, penicillin, streptomycin, etc. ) are prone to drug resistance and cannot effectively cure diseases. Inoculating crabs with biological agents can improve their disease resistance, thus playing a preventive and therapeutic role. Commonly used biological agents mainly include high immune serum and antitoxin.