A blue crab stocking
1. Seed source
The source of fry cultured by blue crab is artificial seedling raising; The second is to catch the big-eyed crab larvae 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 eyes.
(1) Crab fry fishing: The blue crab lays eggs in the sea area with high salinity, and the hatched larvae metamorphose into big-eyed larvae, and then gradually move to estuaries and inner bays to inhabit in the environment with slightly lower salinity. This is the seedling season. Natural crab fry can be caught in the coastal areas of Zhejiang from April to165438+1October, and the peak season is 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 fry: Among the natural crab fry caught, there are often big-eyed larvae mixed with other crab species, which need to be identified and selected. See Table 3-4 for identification and classification.
(3) Juvenile crab cultivation: Juvenile crab cultivation refers to the process of intensive cultivation or artificial cultivation of crab seedlings caught in natural sea areas. After cultivation, the young crabs are bigger, stronger in resistance and higher in survival rate.
2. The natural young crabs are caught, and the individual size varies. The young crabs caught are required to be physically strong, with complete appendages, no mechanical damage and few attachments. Young crabs along the coast of Zhejiang Province are concentrated from mid-June to July, also known as "summer crabs" and "plum crabs", and from mid-September to early June and from mid-September to 10, which are called autumn crabs. Summer crabs can be directly developed into commercial specifications that year, and autumn crabs can only be developed 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.
3 Identification and selection of crab fry quality The environmental conditions of crab fry caught and autotrophic in local sea areas are basically the same, with short exposure time and high survival rate. For example, crabs transported for a long distance must be strictly selected so that sick crabs can 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. Among them, the abdomen and appendages of crustaceans have different colors, such as dark blue, reddish brown and rust color. The crab seedlings with thorns, hooks and sunburn 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 Remove the crab slave. There are a few crab seedlings parasitized at the base of abdominal segment, and the number of crab slaves is 65,438+0 or above. Crab slaves are oval in shape and soft in constitution. They absorb nutrients from the body of blue crabs to maintain their lives, and their normal growth and development are affected by parasitic blue crabs. Therefore, the crab slaves should be eliminated in time when selecting.
(4) Crab seedlings are generally 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.
2. Fried stockings
1 stocking specifications and time: Summer seedlings are generally stocked in June and July, with specifications of 15 ~ 50g, with an average of about 25g. After 3 ~ 4 months of cultivation, it can reach the specifications of commercial crabs of that year. Autumn seedlings are generally stocked in September ~ 10, and the specification is 10 ~ 20g. After overwintering, it can reach the commodity specifications from May to June of the following year. If the overwintering stocking amount is insufficient, 50 ~100g of crab species can be supplemented in March to April of the following year. Fattening and breeding, generally 150 ~ 200 grams of breeding lean crabs are harvested in September ~ 65438+10, and they can reach cream crabs in 30 ~ 40 days.
2 stocking density. From April to May, 50 ~ 100g/ wintering crab should be stocked, with 200 ~ 500 crabs per mu. If it is too small, the density of seedlings can be appropriately increased, and rotation can be grasped in about two months. At this time, it is summer seedling season, and small-sized summer seedlings can be stocked, and the number of seedlings per mu is about 1000 ~ 1500. The stocking time of fattening breeding is from August to 10, and the stocking density can be controlled at about 500 heads/mu according to environmental conditions.
Second, training management.
1. Feed bait
Feeding is one of the important means to obtain the yield of blue crab. Only by mastering reasonable breeding techniques according to the living habits of blue crabs can we effectively give play to the advantages of raising crabs in beach seine. The bait of the blue crab should make full use of the reproduction of natural bait in the pond or the bait organisms that enter the pond through the mesh. Blue crabs are mainly carnivores and like shellfish and small crustaceans. It can be fed with low-value shellfish such as live green clam, short-toothed clam and duckbill clam. Some beaches were originally breeding areas for some low-value shellfish, which should be protected and utilized. At the same time, it can also be transplanted into some annelids such as Nereis and small benthic crustaceans, which have strong self-reproduction ability and blue crabs like to eat. These are good food for blue crabs. In addition, small miscellaneous fish and shrimp and freshwater shellfish such as snails and artificial bait can also be used as supplements when bait is lacking.
According to the feeding habits of blue crabs, artificial feeding is best carried out in the evening. The feeding amount depends on the season, tidal current, water quality and natural bait in the pond. Generally speaking, when the water temperature in the sea area is suitable 18 ~ 25℃ and in flood season, the feeding amount can be increased.
Daily management of blue crab culture
1. bait technology
1 The feeding species of blue crabs belong to carnivorous crabs. Therefore, meat should be given priority to, supplemented by plant-based diet. Commonly used baits include red meat blue clam, muscle clam, duck-billed clam, Scapharca subcrenata, short tooth clam, freshwater river clam, freshwater snail, small miscellaneous fish, miscellaneous shrimp, miscellaneous crab and other small low-value shellfish. Some blue crabs can also be fed with artificial mixed bait. There are many kinds of edible bait, which can be selected according to the actual local resources. As long as the cheap bait is nontoxic and harmless, and the blue crab likes foraging, it can be used as a source of bait to ensure supply, but the bait must be fresh, and the moldy and deteriorated bait must not be fed, otherwise it will seriously affect the healthy growth of the blue crab.
The feeding proportion should be flexibly controlled according to the water temperature, tide, water quality and the activity of the blue crab during the breeding period. For example, when the water temperature is above 65438 05℃, the feeding of the blue crab is vigorous, reaching the peak at 26℃. When the water temperature is above 30℃ or below 13℃, the feeding amount will be obviously reduced. For example, Wenzhou and Taizhou along the coast of Zhejiang Province have suitable water temperatures in May-June and 9- 10, and the feeding amount of the blue crab will increase, so it is necessary to feed more. The water temperature is high in the high temperature period from July to August, and the water temperature is obviously low before May and after 10, so the food intake of the blue crab will be weakened, so the feeding should be less.
At high tide or high tide, blue crabs eat more, but at low tide or after low tide. After changing water at high tide, the water quality is good, and the feeding is enhanced, and the feeding rate can be increased by 1 times compared with usual; If it is rainy, the pool water is turbid or the weather is sultry, the food intake will decrease, and the feeding amount should be reduced appropriately; When the weather is cold, the water temperature drops to about 10℃, and the blue crabs seldom move or feed, so pay attention to feeding less or no bait.
The food intake of the blue crab gradually increases with the growth of the individual, but the ratio of daily food intake to its own weight will decrease with the increase of weight. The relationship between daily food intake and individual size and percentage are as follows: the crab shell is 3 cm to 4 cm wide, and the daily food intake accounts for about 30% of the body weight; The food intake of 5 cm ~ 6 cm days is about 20%; The daily feed intake of 7 cm ~ 8 cm was15%; The daily feed intake of 9 cm ~ 10 cm was10% ~12%; 1 1 cm above 5% ~ 8%.
3 Feeding method The bait should be evenly placed around the crab pond, not in the middle of the pond. Conditional pond, it is best to set up several feeding platforms around the pond to better grasp the daily feeding amount. According to the living habits of the blue crab, it can feed one-third of the bait in the morning and two-thirds in the evening. August Mid-Autumn Festival northwest wind refers to the lunar calendar, the temperature difference between the first half of the night and the second half of the night is widening, and the blue crab is easy to get upset and escape after midnight. It is best to add a proper amount of bait in the first half of the night, which can not only prevent the blue crabs from escaping, but also reduce their cannibalism. In short, the daily feeding amount should be flexibly controlled according to the water quality, weather changes, crab growth and molting.
2. Water quality management
Good pond water quality environment is the basic guarantee for the growth and development of blue crabs. The blue crab has to molt many times in its life to grow into a crab, and molting activities are all carried out in the early morning or after midnight. If there is no fresh and good water quality or insufficient dissolved oxygen, the blue crab will not be able to molt and grow normally, and even lead to death. Keeping the pool water fresh and stable, rich in dissolved oxygen, will make the blue crab easy to shell and grow rapidly, so we must carefully manage the water quality. The basic content of water quality management is to change water and receive water, control water level, adjust water temperature and salinity, maintain proper transparency, pH value and dissolved oxygen, and ensure the freshness and stability of aquaculture pond water.
Changing water reasonably with 1 is the most economical and effective method to improve the water quality environment. Daily water change should follow the principle of "small amount and many times". Generally, change the water once every 3 to 5 days, and change the water more when the tide is high. The change of daily water quantity is 1/3 ~ 1/5 of the whole pool water quantity. During the high temperature period, the water quality in the pool is poor. If the water quality in the open sea outside the pool is good, the water exchange rate should be increased according to the ratio of 1/2 or 2/3, which should be adjusted appropriately according to the actual situation of the pool water. Note that when entering the water, the flow rate should not be too fast and the flow rate should not be too large. In addition, when changing water, we should pay attention to the changes of water quality in the open sea. If the open seawater is found to be luminous, sticky, smelly and has red tide organisms, it is not suitable for launching. The normal water level should be kept at about 1 m, and the water level can be raised to about 1.5 m in high temperature season to maintain the stability of the water temperature in the aquaculture pond.
2 Adjusting salinity When the salinity of seawater in the pond is too low or too high, it is necessary to change the water in time to adjust it, especially in rainy season, fresh water period or rainy day. When the proportion of seawater in the pond is too low, the upper sluice should be opened in time to discharge the low specific water in the upper layer of the pond and then bring it into the high specific water in the middle and lower layers. For the difficulty of natural water absorption in the construction of high beach pool, the seawater in the middle and lower reaches can be pumped by lift pump to adjust it.
3 Stable physical and chemical factors In order to ensure the relative stability of physical and chemical factors in the pool, the temperature and salinity of seawater inside and outside the pool should be detected at any time before and after water change, especially before and after rainfall, to avoid excessive changes in temperature and salinity before and after water change. The transparency of the pool water should be controlled at 20 cm ~ 30 cm, and it is also necessary to maintain a good water color of light yellow, yellow-green and sufficient dissolved oxygen greater than 3 mg/L, and the pH value should be controlled at 7.8 ~ 8.5. Once there is corruption in the pool, it should be removed in time.
4 Adding water quality improvers The water quality improvers commonly used in the cultivation of blue crabs mainly include photosynthetic bacteria and zeolite. Photosynthetic bacteria can effectively improve the ecological environment of ponds, prevent and reduce the occurrence of diseases, and is of great benefit to improve the economic benefits of aquaculture. Its application method is to spray photosynthetic bacteria solution 15 ppm ~ 20 ppm in the whole pond 5 ~ 6 days before stocking crab seedlings, and the concentration of bacteria solution per ml reaches more than 1000000000, and then spray 6ppm~8ppm every10/5 days, which can be used flexibly according to the actual situation.
In order to know the accurate production situation of crab ponds in time, we should not only strengthen scientific feeding and water quality control management, but also do a good job in daily inspection of crab ponds.
1 patrol pool patrol system should be established and improved every day. The inspection contents include gates, dams, escape prevention facilities, water color, water level, feeding situation of blue crabs, living activities, and presence of sick crabs by the pool. Especially in summer and autumn when there is thunderstorm, before thunderstorm, before windless and sultry evening and sunrise in the morning, after a long sunny day, it rains heavily, and the salinity of the pool water changes suddenly, problems are most likely to occur. Therefore, it is necessary to strengthen the patrol of the pool to prevent the blue crabs from escaping and accidents.
2 water quality and crab length detection insist on measuring the water temperature and proportion of aquaculture ponds every day, especially after rain and before and after water change, pay more attention to frequent detection and keep abreast of changes in water quality and environmental factors. During the whole breeding period of the blue crab, the width and weight of the back shell of the blue crab were randomly sampled every 15 days, and the growth of the blue crab in different seasons was known through measurement, so as to adjust the feeding amount in time.
4. Overwintering management Try to reduce the water level in the pond before overwintering, so as to encourage autumn crabs to dig holes on both sides of the ditch and at the bottom of the pond to hibernate. Before the arrival of cold air in the north, try to raise the water level to prevent the autumn crab from frostbite and affect the survival rate of wintering. When the water temperature is lower than 65438 00℃ in the wintering period, there is no need to feed bait. When the water temperature is above 12℃, feed a small amount of bait, and when the water temperature rises above 14℃, feed more bait appropriately. For ponds with small area and poor thermal insulation, sheds can be built to cover the winter.
Disease control of blue crab culture
At present, the research on the causes and prevention techniques of crab breeding diseases is not deep enough, and the principle of "prevention first, combination of prevention and control, prevention is more important than cure, early prevention without disease and early treatment with disease" should still be adopted to prevent pathogenic factors as much as possible. In order to reduce the occurrence of diseases and achieve the goal of high quality, high yield and high efficiency, the constitution and self-resistance of the blue crab should be enhanced.
1. Ciliate disease and filamentous algae attachment syndrome of the blue crab.
This disease usually occurs in the larval stage of the blue crab, and may also occur in the formative stage. The disease has the characteristics of long course and high cumulative mortality.
1 At the initial stage of symptoms, the sick crab has yellow-green and brown fur on its body surface, which makes it slow to move, slow to respond to foreign objects, and greasy when touching its body surface. The existence of ciliated protozoa and green algae such as bell worms and tired branches can be observed under the microscope. In the middle and late stage of the disease, the crab was attached by thick attachments, which caused gill filament damage, dyspnea, secondary bacterial infection, loss of appetite, even no food intake, stagnant growth and development, weak constitution and difficulty in molting, and the mortality rate was about 20% ~ 30%.
The main reason of the disease is that the culture density is too high, the bait residue is too much, the pollution is serious, and the organic matter content in the water is high, which leads to the extreme eutrophication of the water in the culture pond and produces a large number of ciliates and filamentous algae, especially in the high temperature period from July to September every year, which seriously affects the normal growth and development of the blue crab.
3 prevention methods ① keeping the water clean is the most effective prevention method. Do a good job of changing water normally, adjust the water quality, remove the residual bait in the pond in time when draining, spray chlorine preparation regularly for disinfection, and focus on monitoring ammonia nitrogen and pH value regularly. Once the standard is found, change the water immediately, and spray zeolite powder or 100g/m3 ~ 150g/m3 on the whole pond. (2) Zinc sulfate, copper sulfate and ferrous sulfate can be mixed and sprayed on the sick pool according to the ratio of 8: 5: 2, with the concentration of 1.2 ppm ~ 1.5 ppm for three consecutive days, and 0.3 ppm； of "chlorine-rich" can be sprayed on the whole pool on the fourth day; Or spray 1.2 ppm ~ 1.5 ppm of "Fibrinogen" in the whole pool on the first day, and spray 0.3ppm of "chlorine-rich" in the whole pool after changing water the next day. If the disease is serious, it can be reused after 7 days to 10 days, which can kill the attached organisms on the crab. After disinfection and killing pests and diseases, the bait is mixed with antibiotics to make medicinal bait, and 0. 1% ~ 0.2% ecdysone is added, and 7 days is a course of treatment, which can comprehensively and effectively control diseases.
2. Crab molting failed
The failure of molting of blue crab is one of the most serious situations in the whole growth period of blue crab. The disease is mainly caused by water environment mutation and bacterial infection.
Symptoms of 1 The disease usually occurs in autumn every year. Whenever the first cold wave comes, a large number of blue crabs weighing about 150g are easily infected with Vibrio, and gradually deteriorate and die in the process of not being caught and raised. The body fluid of the sick crab is white and turbid, and the muscles of the basal ganglia are milky white. Healthy crabs are blue, and when they break their feet, they will overflow with white mucus, which is often called "white mans disease". Infected ponds are prone to repeated infections, and the mortality rate can reach 30% ~ 80%, which has a particularly serious impact on aquaculture production.
2 reasons ① In autumn, the water temperature of 22℃ ~ 25℃ is the most suitable condition for the reproduction of pathogenic bacteria such as solitary bacteria in water. The decrease of water temperature will reduce the vitality and disease resistance of the blue crab, and pathogen infection is the root cause of the disease. ② The disease is also related to the special physiological and ecological structure of the blue crab. In autumn, the water temperature is between 25℃ and 28℃, which is in the stage of centralized reproduction and molting of the blue crab. Generally, molting takes 2 ~ 3 days to harden, and it is easy to be infected with germs. At this time, if the environment changes suddenly and the water quality and coating quality are poor, it is easy to hinder male and female mating and cause a large number of deaths.
3 Prevention and control methods ① Maintaining good water quality is the most basic measure to prevent diseases, and external pollution and foreign pathogen infection should be strictly prevented during the breeding process. ② Disinfect with 25ppm quicklime or 2ppm bleaching powder alternately every 7 days before the onset of the disease, so as to improve the water quality and kill pathogenic bacteria in the water. At the same time, some blue crabs can shed their shells in advance and promote the division between crabs during the molting period. ③ Disinfect the whole pool with 0.33ppm dichlorohydantoin or 0.8ppm bromochlorohydantoin for 2 ~ 3 days, and take doxycycline orally for 5 ~ 7 days, and the effect is good.
3. Blue crab macular disease
Macular disease of blue crab usually occurs in the juvenile or adult stage after the ⅷ stage, which is a common disease in the current culture process, with a long course of disease and high mortality rate, second only to molting failure.
1 At the initial stage of symptoms, yellow spots appear on the crab's chelates and crustaceans, and then rust spots appear on the abdominal crustaceans, or a yellow mucus is secreted at the chelates. The activity function of the pincers decreased, and they lost their activity regularity and feeding ability. The center of the upper abdomen spot is slightly concave and reddish brown. Late ulcer spots expand and connect with each other, forming irregular large spots, with deep central ulcer and black edges. When crustaceans are cut open, light brown foreign bodies the size of pepper seeds can be seen in their gills.
There are many kinds of pathogenic bacteria causing this disease, which are widely distributed. The direct cause of this disease is the damage of the upper epidermis of the carapace and the invasion of chitin-decomposing bacteria during the collection, transportation and breeding of the blue crab. The incidence frequency and infection rate increase with the increase of water temperature, and the incidence time is usually in the season with high water temperature and plenty of rain.
3 prevention methods ① feeding fresh bait and bait with high activity, such as shellfish, can reduce the occurrence of the disease. ② In the process of fishing, transporting and breeding crab seedlings, careful management and operation should be carried out to prevent crabs from being harmed. Stocking density should not be too high. (3) Keep the water fresh. Before stocking, the seedlings should be soaked in 200ppm formalin solution for 2 ~ 3 minutes to kill parasites and pathogens on the crustacean surface. (4) Try to keep the salinity of the water in the culture pond stable, regularly use 25ppm quicklime or 2ppm bleaching powder for disinfection, and sprinkle the tea residue leaching solution all over the pond every month, so as to make the blue crabs shed their shells and reduce the occurrence of diseases. ⑤ 0.5ppm dibromohydantoin can be used to disinfect the sick pool for 3 days. At the same time, combined with oral administration of compound ciprofloxacin, the dose is 5 grams per100 kg per day for one week, which can prevent and alleviate the occurrence of diseases.
4. Yellow crab water disease
Yellow water disease of blue crab usually occurs in July-August and September-65438+1October of the following year, which is very harmful to the culture and production of blue crab.
The symptom of 1 was named after the muscle liquefied into "yellow water" before dying. The annual incidence rate is higher than that in autumn, and the mortality rate is more than 70% in severe cases, which directly affects the healthy growth of blue crabs.
The main causes of the disease are poor water quality and sediment in high temperature season, and a large number of bacteria multiply. The large temperature difference between day and night from July to 65438+1October aggravated the occurrence of the disease. In the peak season of shrimp culture in spring and summer, the blue crabs raised in shrimp and crab polyculture ponds are resistant to low-dose white spot virus. However, when a large number of sick shrimps die and deposit at the bottom of the pond, once the fresh feed in the pond is short, the blue crabs infected with "Yellow Water" bacteria but not yet sick will quickly get sick and start to die in large numbers with the help of high-dose white spot virus infection after eating these dead shrimps.
3 Prevention and control methods Before the onset of the disease, use 25ppm quicklime or 0.3ppm dibromohydantoin to prevent and control the whole pool. At the same time, combined with oral administration of compound ciprofloxacin, the dose is 3 grams per 100 kg crab every day for 3 days, which can prevent the occurrence of this disease. The sick pool was disinfected continuously for 3 days, and the compound ciprofloxacin was taken orally, 5 grams per 100 kg crab body every day for 5 ~ 7 days, which had a good therapeutic effect.
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