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Green crab breeding technology
Serrata Scylla serrata (Forskal), abbreviated as blue crab, is commonly known as cricket. Guangdong said that the crabs, Taiwan, Fujian called red clams; South Zhejiang clams, the Philippines called mud crabs. Because its head breastplate is blue, the front edge has 9 side teeth serrated, so it is named Serrata blue crab. The crab has a large individual body and a sweet flesh. It is a well-known edible crab in China and has high nutritional and commercial value. As early as 1891, it was artificially farmed in Humen, Guangdong Province. So far, it has a history of more than one hundred years and is well-known domestically. outer. First, the morphological characteristics of blue crabs Green crab head breastplate slightly oval shape, smooth surface, the central slightly elevated, the partition is not obvious. A surface and appendages are blue edge color. There is an obvious "H"-shaped dent between the back stomach area and the heart area. The frontal has 4 prominent triangular teeth, which protrude from the inner orbit. The front edge has 9 medium-sized teeth. The distal teeth are small and sharp. Point forward. The chelafoot is large and the two chelators are asymmetric. There are 3 ratchets at the leading edge of the long section, 2 spinousles at the posterior edge, 2 blunt teeth at the outer end of the wrist joint, and 1 strong burr at the inner end horn; the palm section is swollen and smooth, and the male individual is particularly swollen, with 2 long sides on the back. The ridges have 1 spines on their distal ends and 1 line groove on the medial and lateral sides of the knuckles. The gaps between the two fingers are larger, and the teeth on the inner edges are large and blunt. The front and rear edges of the first three pairs of step knuckles are short-haired, and the front-to-back knuckles and knuckles of the stepping feet are flattened and suitable for swimming. Male abdomen was wide-angled triangle, and the distal edge of section 6 was concave. Its margin was straight, with straight edges on both sides. The distal edge of the distal segment was blunt, and the female abdomen was wide-circular. Second, the ecological habits of blue crab (a) living habits 1. Habitat Green crabs are beach-dwelling swimming crabs that live in tidal flats or muddy sandy beaches. They prefer to stay in mudflats and rock seams. Cave dwellers during the day, foraging around the night. Especially during the high tide night, it appears to be more active. Because of its sensitive eyes and tentacles, it is able to move freely at night. Summer crab activities are more frequent, and when the low tide is shallow, the water is often hidden at the bottom of the mud to avoid heat, and sometimes it can be seen in groups. During the dry heat, the blue crab walks away from the beach with high temperatures and cools off. In winter, there is less activity. When the weather is cold, it darks near the low tide for winter, and the size and depth of caverns increase with the size of the individual and the tide area. Deepening, caves in the high tide area can sometimes reach more than 1 meter. The blue crab moves backwards and forwards frequently in the water depending on the footsteps, but in most cases, it moves with the flow, and it can quickly recede when it is frightened or encounters obstacles. It crawls on the beach side and feels agile and moves freely. . 2. Habitat conditions Green crabs are wide-temperature, wide-salt and salty marine crabs. Their survival water temperature is 7 to 37C. The suitable water temperature for growth is 15 to 31C. The optimum water temperature is 18 to 25C. When the temperature is 15C or less, the growth is slowed down and the water temperature drops to 7 to 8.5. At C, stop feeding and activities and go into hibernation and burrowing. When the water temperature stabilizes above 18C, female crabs begin to lay eggs, and the young crabs frequently grow and hulling. When the water temperature rises above 37C, the crabs do not ingest food. When the water temperature rises to 39C, the gray crab's dorsal armor appears gray spots. The body is gradually aging and dead. The crab's survival salinity is 2.6 to 55 ‰, and the range of adaptation is 6.5 ‰ to 33 ‰, and the optimal salinity is 12.8 ‰ to 26.2 ‰ (specific gravity 1.010 to 1.021). It is difficult for crabs to adapt to drastic changes in salinity, and mutations in salinity can cause both "Hongmang" and "Pangong" diseases and even death. Therefore, in the rainy season of each year, due to sudden heavy rain or continuous rainfall in a short period of time, the abrupt changes in the salinity of artificial breeding ponds increase the mortality of blue crabs. The crab has strong drought resistance. After the water is removed, as long as there is a small amount of water in the larvae and the silk is moist, it can survive for several days or dozens of days. 3. The diet of green crabs of blue crabs is very complicated, mainly animal foods. The food composition is dominated by mollusks and small crustaceans, and bivalve shell edges, twisted parts, gastropods, incomplete screw shafts, stumps and heads of crabs often appear in stomach contents. Breastplate fragments. Green crabs also often feed on beach worms, and also eat small fish and shrimp. Sometimes there are also pieces of stems and leaves found in the stomach. Artificially cultivated blue crabs have no strict choices for bait, small fish, shrimp, and small shellfish (blue pheasant, fork's muscle, river bream, clam, etc.), soybean cakes, and peanut cakes can be eaten. There are habits of killing each other in the same category, and they often eat soft shelled crabs that have just shelled. (B) Breeding habits The breeding season of blue crabs is longer, but varies from place to place. Guangdong is from February to April and from August to September each year, of which from March to March is the peak period; from March to October in Xiamen, Fujian Province, Zhejiang Province. From April to October. From late May to June and from late August to September, it is a prosperous period of breeding; from September to October in Shanghai, Taiwan can breed almost all year round. Crabs generally reach sexual maturity within a year. Generally female crabs with a shell width of 8 cm and a weight of 150 g or more can be mated. Prior to mating, female crabs first undergo genital shelling and male crabs mate before their new shells have hardened. The mating time can last 1 to 2 days. During the mating period, blue crabs have no appetite and do not eat even if they do not feed. After mating, the sperm is stored in female seminal vesicles and survives for several months. After the female crab egg matures, it enters the seminal vesicle and sperm with the fallopian tube, and then the fertilized egg is released from the female genital pore and adheres to the bristles of the abdominal limb. The eggs that emerged were initially yellow, at which time the female crab became an egg-bearing crab. Female eggs lay about 2 million eggs, but the eggs they hold are only one part of them. Female crabs spawn at places where the water surface is wide and where the water is clear. The female crabs living in the estuary have to spawn in the sea to lay eggs. Therefore, the blue crabs in the natural sea area often have to leave the shore for a short distance to "dive into the deep." egg. The hatched larvae come to the shore with the tide and then grow up in the intertidal zone and swampy land. The juvenile crab with a width of 1-2 cm can be caught every May in the Zhejiang coast. Young crabs in the sea area are concentrated from late June to early July (myeon crab) and from mid-September to October (autumn crabs). The development of larvae is divided into two stages: the juvenile larvae and the big ocular larvae. It requires a total of 6 times of shelling and metamorphosis. It is the first young crab and lasts for about 23 to 24 days. (c) Shelling growth The growth of blue crabs is discontinuous. Shelling is a sign of its growth. Only when it is shelled, can it be grown. The young crabs decapsulate the shells for an average of about 4 days. The shelling time is gradually extended. Months later, it took more than one month to remove the shell once, and it took more than one hundred days to grow from the first young crab to the 10th young crab. Green crab shelled 13 times in a lifetime, the last (13th) shelling, mating with the blue crab, closely related to reproduction, called "reproductive shelling." The newly hatched crab body is in a soft state and is called "soft shell crab". It absorbs a large amount of water on the bottom of the body and relaxes the body. Generally it begins to harden within 6 to 7 hours, and the individual enlarges significantly within 18 to 19 hours. weight. After shelling, shell length increased by 30% to 40%, and weight increased by 70% to 100%. Under normal conditions, the new shell hardens completely after 3 to 4 days. Third, aquaculture technology (a) green crab seed stocking 1. The source of seedlings originated from blue crabs is the artificial seedlings; the second is the big eye larvae (crab seedlings) in the catching area; and the third is the catching of natural crab species. Artificial nursery seedlings are neat and pure, and they are still in the experimental stage. Large-scale production and seedling raising techniques have not yet fully broken through. Before the artificial breeding technology has yet to make productive breakthroughs, catching crabs and crabs in natural sea areas is still the main source of seedlings for artificial breeding of blue crabs. (1) Large-eyed larval fishing 1 Crab-fishing: Blue crabs spawn in higher salinity areas, and the hatched larvae metamorphose into large ocular larvae and then gradually move to the estuary and in the low salinity environment of the inner bay. It is seedling season. Natural crabs can be caught in the coastal areas of Zhejiang from April to November. The peak season is May to June and August to September. Crab fishing methods mostly use fixed nets, push nets and hand-printing nets. All localities choose according to the specific conditions of the tide and storm. 2 Identification of crabs: In the natural crabs that are caught, there are often other large-eyed larvae of crabs that need to be identified and selected. See Table 3-4 for identification details. 3 Juvenile crab cultivation: Juvenile crab cultivation refers to the process of intensifying the development of juvenile crabs from crabs that are harvested or cultivated in natural sea areas. The nurtured juvenile crabs have larger individuals and stronger resistance, and have a higher survival rate. (2) Natural juvenile crabs, natural and juvenile, are harvested in small and large bodies. They are required to have young crabs with strong physique, intact appendages, and no mechanical damage or attachments. In mid-July (also known as "Summer Crab" and "Mei Crab") and from mid-September to mid-October (called Autumn Crab), Xia Crab can directly develop commodity specifications in the same year, and autumn crabs must go through the winter. Develop product specifications. After the crab has been caught, the exposed time should be short, especially when it is hot and hot in the summer. It is not recommended to expose the air when the temperature is above 28C. It should not exceed half a day when the temperature is above 28C, and it should not exceed 2 days when the temperature is below 25C. The time from capture to stocking is increased. Shorter the better. Too long can cause death. (3) Identification and selection of the quality of the green crab seedlings Self-caught crabs in the local sea area, due to the same environmental conditions, short exposure time, the general survival rate is high, such as long-distance transport of crabs, subject to strict selection The elimination of sick crabs can be reared, and the methods for selection and identification of the seedlings are: 1 Select a healthy crab. The crustacean of the robust blue crab is blue-green, full and complete, with intact body, sensitive sensory response, strong activity, and not easy to catch; swimming feet and chewing feet are indispensable and disability, and the lack of stepping cannot exceed 3, if If the step is broken or injured, the remaining leg can be broken at the joint between the base section and the joint. The new appendage will be regenerated in a short time. If it is not dismantled, the stump will fall off. A lot of body fluids cause death. Where the carapace, abdomen and appendage have different colors (such as dark blue, reddish-brown, rust, etc.), the quality of the crabs that are thorned, hooked, and sunburned is not good. 2 no disease. Distinguishing disease crabs can be judged from the color of the foot base muscles. The flesh color is blue, the muscles of the limb joints do not subside, and those with elasticity are healthy seedlings. For example, the muscles are yellowish-red or have white spots, and the muscles of the limbs are subsided. Inelastic, it is not suitable for farming. 3 Excluding crab slaves, there are a few crabs that have one or more crab slaves on the inner base of the ventral section of the abdomen. The crab slaves are ovoid, and their bodies are soft to absorb the nutrition of the blue crabs. The parasitic crabs affect normal growth and Development, so the selection should promptly remove the crab slave. 4 Crab transportation young crab transport tools are generally hard-framed or wooden boxes. Spread a layer of wet grass on the bottom, put a layer of crab, and then cover with a layer of wet grass, so that the young crab will not be bruised. Do not overlap too much. Finally, cover the screens with hard screens to facilitate seawater dripping on the way and improve the survival rate of transportation. 2. Seed stocking (1) Stocking specifications and time: Summer seedling stocking is generally from June to July, specifications are 15 to 50 grams (average 25 grams) or so, after 3 to 4 months of breeding, the crab can reach the product specifications; Autumn seedling stocking generally in the 9 to 10 months, specifications in 10 to 20 grams, winter cultivation to the following year 5 to June, up to the product specifications. If the amount of wintering stocks is not enough, it can be supplemented with 50-100 grams of crab species from March to April in the second year. Fattening and breeding, generally from September to October, 150 to 200 grams or more have been mated with the thin crab, breeding 30 to 40 days up to the crab. (2) Stocking density. 4 to 5 months of stocking 50 to 100 grams / only overwintering crabs, 200 to 500 seedlings per acre is appropriate, such as small size can be appropriately increased seedling density, about two months can be arrested. At this time it is the summer seedlings seedling season, can be stocked small-sized summer seedlings, the number of acres of seedlings per acre of about 1000 to 1500 is appropriate. Feeding time for fattening and rearing is from 8 to 10 months, and stocking density can be controlled at 500 pieces/mu depending on environmental conditions. (B) Cultivation Management Feeding bait feeding is one of the important means for obtaining the production of blue crabs. According to the feeding habits of green crabs, it is only possible to effectively exert the advantages of crabs on the shoal purse seine. The food of the blue crab should make full use of the propagation of natural food in the pond or the food organisms entering the pool through the mesh. Green crabs are mainly carnivorous. They eat shellfish and small crustaceans. They can feed low-value shellfish such as live bluebottles, short-toothed breams, and duck-billed breams. Some shoals originally used to be low-value shellfish. It should be protected and utilized. At the same time, it can also be transplanted into some annelids (such as Nereis) and small benthic crustaceans. It has a strong self-breeding ability and green crabs prefer to eat. These are good live baits for blue crabs. In addition, shellfish (such as snails) and artificial diets for small trash fish and freshwater species can be used as supplements for lack of bait. According to the foraging habits of blue crabs, artificial feeding is best done in the evening. The amount of feeding depends on the season, current, water quality, and natural food conditions in the pool. In general, when the water temperature in the sea area is suitable (18 to 25C) and during tidal periods, the amount of feeding can be increased. The total amount of crabs in the pool can be 5 % to 10% feeding, should be fed in small amounts during small tides and abnormal weather in rainy season. Feeding sites should be broadcast evenly on the beach. After feeding, check the feeding conditions of blue crabs. The next day, if there are any left baits, feeds should be suspended to find out the reasons. 2. Water quality management During the tidal period, seawater can naturally enter and exit, and the water in the pool can be fully exchanged. There is no water quality problem. Before the arrival of a small water tide, check and repair the seepage water of the earth dam, increase the height of the overflow outlet, and store the full water level. Maintain the water level at 0.5 meters above the surface of the beach. In case of heavy rain, allow the overflow dam to overflow the fresh water in the upper layer to prevent a sudden drop in the salinity of the sea and cause the occurrence of blue crabs. (3) The key to the daily inspection of the success of beach purse seine crabs is the ability of the facilities to resist wind and waves, as well as the measures and effects of avoiding flight. Therefore, farmers must patrol every day to watch. After every ebb tide, check whether the earth dam has water seepage or water leakage, whether the fence piles have collapsed, whether the fence has been damaged, if any problems are found, repairs should be promptly made and blue crabs should be active at night. Frequently, during high tides, it is easy to stimulate the nets to escape. When the tide overflows the dam, blue crabs turn around the fence. If there is a hole in the fence, groups of blue crabs will flee here. At this point, the nets should be repaired immediately. In addition, when the water quality is low in a small tidal pool, it is easy to make the crabs burrow and escape. It is also necessary to pay attention. The predators of the shoal purse seine crab mainly include tigerfish, Chinese pond pupa, and finger horse licks. They often eat during the crab shelling period. Therefore, during the breeding period, they can be exposed to tides during each tide period. The dry pool captures and removes predators, but it can keep the pelican and pike in the pool, which is beneficial for cleaning up sludge and baits at the bottom of the pool, and can coexist peacefully with the green crab and increase additional production. (4) Harvesting of green crabs in the intertidal zone should be timely arrested, take arrest measures, catch large and small, and trap fat and thin, so as to obtain higher economic benefits. September is the mating season of blue crabs. Male crabs should be collected in due time because male crabs lose weight after many times of mating, which reduces the food value of crabs and causes a large number of deaths. The female crabs after mating are approximately the same. After 30 to 40 days of feeding, it will become a crab. If it is over-riped, it will result in holding eggs and crabs, which will also reduce the value. In addition, the water temperature in the sea area is declining. It is difficult to raise green crabs in winter, and it is also required to collect them in a timely manner. Generally, it is required that the crabs in the pond be captured before the end of October. The collection methods for the green crabs in the area include: (1) Lighting capture , According to the blue crab like to climb the pool or tide habits at night, lighting can be used to dig the network to pick up the method; (2) dry pool hand catch and capture: freehand touch is an old and practical crab technology Crab body will not be damaged, but there must be skilled techniques. Use crab crab. Basically, the crab can be netted, which saves time, but the crab is easy to be injured. Be careful when you operate it. The captured blue crabs must be bundled to prevent them from being bitten by each other. It should be stored in a cool and humid place during high temperatures in summer and covered with water and grass when it is cold. (5) Polyculture In recent years, the monoculture type of blue crabs has been rare, especially in the intertidal zone with green crabs, which are multi-species polyculture. The type of polyculture is relatively complex, and the basic principle is through appropriate mixing. The cultivation of other economic types can purify the sediment, form and maintain a suitable biological structure in the pond, and create an ecological environment suitable for the living and growing of blue crabs and polycultures. Currently, the polyculture species include fish, shrimp, shellfish, and algae. More than 10 species. (1) Shrimp: such as Chinese shrimp, hairy prawn, prawn, Japanese prawn, new amount of prawn, and white-tailed prawn. The stocking specifications of the shrimps require that the seedlings more than 3 cm in length after being raised, the seedling quantity is generally about 1000 to 2000 tails/mu, and the growth rate is faster than the shrimp ponds in the tide. When the water temperature is suitable, the seedlings are released one month later. You can start catching. (2) Fish: The main species are: cockroaches, barracudas, black cockroaches, mudskippers, etc. The pooled organic matter is an excellent bait for these fishes, and the amount of seedlings is generally between 20 and 500 per mu; 3) shellfish: mainly polyculture of some benthic shellfish, such as cockroaches, loach, raccoon, Philippine rice dumplings, barley, etc.; as a case of polyculture, for example, put the plot to control the area of ​​the pond in 20 % The following is appropriate, raise the surface of the shellfish every year to rest, select the flat surface of the central beach after the deep turning, flattening can be placed after the seedlings, each mu of painted seedlings in the amount of 30 ~ 50 kg is appropriate. (4) Algae: The polyculture of Taiwan's blue crabs and G. striata (Taiwan called asparagus) is more common. The mixed amount of algae can absorb a large amount of dissolved organic matter in the water and increase the dissolved oxygen in the water, which is more conducive to the growth of blue crabs and other economic animals in the pond. Mixed-stock should pay attention to matters: (1) the density of polyculture should not be too high, the species should not be too much, should be based on cultured blue crabs, daily management methods are also carried out by the method of breeding green crab, such as polyculture other varieties of miscellaneous And high density, it became a distraction and affect the growth of blue crabs. (2) The selection of polyculture species depends on the conditions of the pond. In particular, the type of pond bottom conditions is in accordance with the habitat of the cultured species. For example, the cross-year culture species is undesirable. In particular, fish species cannot generally be allowed to overwinter in the pond. The number of casualties that will be used for transplanting will be large. Only the raising of the seedlings will be allowed. The pre-occupation condition of the catchers can be met before the low temperature arrives.