First, the early propagation of seedlings refers to the large-eyed larvae that were hatched and hatched from January to March. Several issues in the cultivation of early crabs and crabs are summarized below. 1. Cultivating Pro-crabs The first batch of early breeding seedlings in the crab seedling field of Suining County, Jiangsu Province in 1995 were fertilized by mating crabs, moved into a nursery room to strengthen cultivation, and passed embryo development and hatched into larvae. The total number of days was about 30 days. The number of hatches per day is very small, and it is not possible to keep the animals in sync. After microscopic examination: embryonic development of eggs, there is a big difference between crab and crab. It is the eggs of the same female crab. The degree of embryonic development is also inconsistent, that is to say, the developmental degree of each development stage is very different, there is a heartbeat period, there is a point period, and hatching is not synchronized. Incubation period is as long as 23 days, the number of days is elongated, and the larvae's constitution is relatively weak. It can be seen that the embryonic development of incubating crabs is incomplete and the hatching period is too long, then the developmental metamorphosis is uneven and the survival rate of the cultivated crabs is low. On the contrary, the crab embryos are fully developed, with their hatching and synchronization concentrated, their hatching period short, their survival rate high and the larvae robust. The second batch of crab seedlings in Suining County was hatched from February 7 to 14, 1995. The hatching period was 8 days. From the fertilization of egg to the hatching of Zl, there were 52 days. The hatched larvae were active, and the developmental metamorphosis was relatively uniform. The number of crabs raised is greater. Another example is the first batch of nursery for famous special aquaculture bases in Tianjin Dagang Oilfield. Its incubation period is February 19-25, 1997, and the incubation period is 7 days. From fertilization to hatching of Zl larvae for 69 days, the hatched larvae Robust and well-developed, the number of cultivated crabs is high. In both years, the two nursery farms in March conducted large-scale nursery. Their embryonic development was more than 80 days, and the hatchlings had better physique and quantity. Therefore, after mating and fertilizing production of crabs, effective measures must be taken to cultivate good eggs and crabs. It is advisable to transfer the crabs in the water at a low temperature of 3°C-6°C for a period of time to simulate the wintering period so that the embryos are in a relatively stationary state. It is conducive to hatching and raising seedlings. 2. Guaranteed supply of live food 2.1 Open-baited unicellular algae such as Chaetoceros, Chrysophyta, Platymonas and Chlorella, live organisms such as rotifers and Artemia nauplii are all good opening baits for crab Zl. At the same time, it can also purify and stabilize the water quality of the nursery water, thus increasing the developmental metamorphosis rate of the Zl-Z3 larvae. The temperature of the freshwater in the fresh sea of ​​early breeding seedlings is in the range of 10°C to 0°C. In order to ensure the feeding of bait, live bait should be cultivated in advance. In the early days of the flounder, the density of bait in the water is controlled at 100,000/ml and is indispensable. 2.2 Feeding of palatability bait means feeding of palatable bait after Z4 larvae. From the beginning of Z4 larvae, during the Z5, M (eyelid larvae) stage, the larvae grew and the food intake increased. When the food is scarce and scarce, the same type of mutual killing is serious, so at this stage, the supply of bait should be timely and appropriate. The cultivation of large artemia bugs requires more quantities, making it difficult to ensure supply, and the cost is relatively large. It is economical and practical to purchase copepods on the coast for storage, which is completely suitable for feeding of early-flushing seedlings. 3. Strengthen management During early breeding period, the temperature, water temperature is low, the light is weak, and the live and palatable biological feed is in short supply. Therefore, the management of nursery management is different from that of conventional nursery (Four and May seedlings). Specific requirements: 1 To reduce water quality Pollution, Zl will need to change water at the beginning. The water exchange capacity is increased by more than 1 time compared with the conventional nursery. In the Z4 stage, depending on the degree of pollution, it is necessary to pour the pool at any time, and at the same time, the amount of feed should be appropriate. 2 The larval density of early propagation seedlings is generally controlled at 200,000/m3 and the density should not be too large. 2 The water temperature difference between nursery and water is controlled at about 0.5°C. Second, there is no precise definition of early-stage seedlings. We believe that the crabs in the pool on April 20th (in the middle and lower reaches of the Yangtze River) need to increase the water temperature to cultivate young crabs. The large-eyed larvae that were raised before this time can be considered as early propagation seedlings. Generally, young crabs are cultured in early and late plantings from early February to late March. The hatching crabs that have emerged too early have not passed the winter, and the emergence rate is very low. The big ocular larvae that are bred are congenitally deficient; when the time is late, the advantage of early seedlings is lost. The juvenile crab out of the pool is too small and directly affects the breeding of adult crabs. . 1, before the preparation of the seedlings 1.1 cloth water grass cloth plants around the pond, water plants accounted for about l/2 area around the pool. Before April, only the peanut roots are generally available. Where conditions permit, some water hyacinths such as water hyacinth or water lettuce can be stored in the greenhouse before winter. If there is no water peanut, you can put it in the water with a willow root or a brown bench stick. Water, grass, etc. must be disinfected before going to the bottom of the pool, and can be soaked with bleach or superior chlorine for half an hour. 1.2 Clear ponds and influent ponds Clear ponds should be planted in the first half of the next half-matured period. Every 100 square meters is to be splashed with about 10 kg of quick lime and 0.5 kg of bleached powder, and drained after two days. One week before the seedlings were inoculated, the inlet was filtered with a 60-mesh or 80-mesh sieve, and the seedlings were sprinkled with quicklime for 3-5 days before seedlings were sprayed. Test the water in the pool and keep the pH around 7.5. Raise the temperature of the water to about 20 °C (or close to the pond temperature at the nursery). If it is a coastal crab, the pool water salinity should be adjusted to 2‰-3‰. 1.3 The preparation of winter food The basic food in winter ponds is very scarce. It is possible to cultivate plankton by using greenhouse warming in advance. However, it is not economical. , And the crabs will not need fertilizer after 2-3 days of becoming a young crab. Therefore, we do not use fertilizer and water for young crabs. There are several types of bait that can be prepared at the moment: (2) buying frozen copepods; (2) buying a small amount of fresh eggs, hatching them in salt water before hatching, and hatching when the seedlings hatch from the pond. Feed, (3) a microencapsulated feed containing high-stable Vc; 4 using 1-2:1 fish gizzards and eggs after steaming through a 40-60 mesh sieve; 5 soymilk and egg yolk. Prepare these feeds and the crabs will be ready for feeding. 1.4 During the process of raising crab crabs into V-stage juvenile crabs, juvenile crabs are more delicate and susceptible to illness. Therefore, some medicines should be prepared for prevention, such as oxygen-supplying agents, oxytetracycline, and Crab-tai. 2, under the management of the post-emergence 2.1 crab crab seedlings under the long-distance transport, cocoon dry due to lack of water, it is not appropriate to immediately put the crab into the water, to prevent the silk suddenly absorb water and cause discomfort. The seedling boxes should be opened. Each box should be showered with pool water or the seedling box should be immersed in the pool water. After 3-5 minutes, the seedlings should be placed in the pool. The density of seedlings can be controlled at 100 square meters for l-3 kg. 2.2 The bait should be fed immediately after feeding the crab. The first feeding is more appropriate, and the feeding amount accounts for about 20%-40% of the seedling weight. After an average of 4-6 hours, the feeding amount can be reduced to 10%-20% of the seedling weight. Until crabs metamorphose into young crabs. After the crabs become Phase I juvenile crabs, their habits change, and they only need to be fed with micro-encapsulated bait or steamed eggs, and the amount of feeding will be appropriately adjusted according to the survival rate of the crabs. Hours can't be eaten, and there is no residual bait for the best amount in 2 hours. Mean 6-8 hours feeding. As the juvenile crab grows continuously, the amount of feeding increases, and the type of feeding can also increase the number of bean cakes, steak meat, and snail meat. After the fish is steamed or the egg yolks are removed from the crab, they can be removed. 2.3 The temperature of crab seedlings in the lower pool is about 20°C, and then it can be slowly increased by 1°C every day. Conditioned cultivation ponds can be raised to about 25°C and kept there. Under this temperature control, the crabs begin to metamorphosing into stage I juvenile crabs after 1-4 days. It is required to measure the water temperature once every 1-2 hours, and measure 4 to 6 points per pool. Record well and if the temperature drops, warm immediately. Special attention should be paid to the temperature difference between rainy days and day and night. 2.4 Water quality control The pH value of the water in the pool is measured on a daily basis with a precision pH test paper. If the pH value is found to be less than 7.0, quicklime may be used to disperse the whole pool with a concentration of approximately 510ppm. It should not be changed too suddenly. Before the large-eyed larvae metamorphose into juvenile crabs, they may not change their water. For example, if water quality is relatively stable, water may not be added. After the first phase of juvenile crabs, fresh water or a little change of water is added every 2-3 days, changing water or adding water accounts for l/5—l/8 of the pool water. The temperature difference between the new water and the pool water should not exceed 2°C. The water level can slowly rise to 70-80 cm. The transparency is controlled at 35-40 cm. 2.5 Oxygenation and Disease Prevention Oxygen pumps are not stopped under special circumstances. Frequently inspect the underwater stone to prevent clogging. In the event of a power outage, the whole pool will be sprayed with fast oxygen 2 times a day, with an amount of 3-5 g/m2. Or spray once a day with 5 to 10 grams of slow oxygen donor per square meter. As the young crabs in I-V stage have more diseases, we should do daily preventive work. In the feed often add a certain amount of oxytetracycline, furazolidone, etc., weekly spilled crab ponds in the pond, excellent chlorine net, etc., can play a certain role in prevention. In addition, we must prevent the entry of predatory creatures and timely kill animals such as frogs entering the pond. 3. Sub-pooling and catching 3.1 Timely sub-pool When the water temperature is controlled between 20°C and 25°C, it takes about 20-25 days from the big-eyed larvae to the V-stage young crabs, with an average of about 5 days. quickly. If the survival rate is relatively high, the density in the pool will become larger and larger, easily causing fratricide, uneven feeding, and deterioration of water quality. At this time, it is necessary to divide the pool in time to promote its rapid growth and improve the specifications of the outlet. It should be noted that ponds used as sub-pools should also be strictly cleared ponds, filtered into the water, put into water plants, adjust the water quality, water temperature and so on. 3.2 From the end of April to the end of May, the temperature of the outdoor water reached 15°C and the crabs began to ingest food and clam shells. At this time, you can start catching and selling. Before the capture, heating can be stopped, so that the water temperature in the pool is basically the same as the water temperature outside the shed, so that the young crabs can be better adapted to the pond. The early fishing can be directly collected on the aquatic grasses, and the latter can be rushed to the water for trapping. 3.3 Preservation of pond crabs The young crabs that control the growth of young crabs and the young caves that have caves are all small in size and can be stored in ponds. Deepen the pond water to 1.2-1.5 meters, add water and grass, reduce feeding properly, and feed 1 plant vegetable diet, such as corn, wheat, bean cake, etc. for 3-5 days. Change the water and splash it in half a month. A quick lime, this strict control of its growth, to the end of the year can be cultivated a certain number of crabs.
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