Sawn-edge crabs are commonly known as blue crabs (hereinafter referred to as blue crabs). They are well-known edible crabs. They have delicious meat flavors, more ovary flavor, and are rich in nutrients. They not only have high commodity value, but also have nourishing and strengthening functions. They also have medicines. Use it. It is widely distributed in the coastal areas of the 30th latitudes of the north and the south, and the coast of the south of the Yangtze River estuary is rich in China. It was built 100 years ago to build ponds, but the output is not high and the scale is small. In the past 10 years, with the gradual reduction of natural marine crabs, artificial breeding of blue crabs has rapidly developed. However, the supply of crabs has become a bottleneck for artificial breeding. The supply of natural crabs is in short supply, and people in the aquatic industry began to actively explore the cultivation of artificial crab seedlings. Since 1990, the author has been conducting research on blue crab breeding and has done a large number of productive artificial seedlings. We hereby summarize experiences for the general farmers to promote The development of blue crab breeding. The reproduction season of blue crab varies from place to place in the breeding season of crabs, and is mainly related to water temperature. At temperatures above 18°C, their feeding and activities were normal and the gonads gradually developed. In the natural coastal areas of Guangdong Province or in the crab ponds, mature ovarian crabs can be seen on the anniversary. However, the general breeding season is March-June and September-October. When the salinity changes greatly in hot weather or at low temperatures, mature blue crabs are less common. This may be due to the high water temperature and low salinity affecting ovarian development. The annual temperature and water temperature in the coast of Zhanjiang are relatively high, and they are relatively stable. There are blue crabs that can hold eggs every year. However, the water temperature is low in January and February, and it is relatively rare to see green crabs. Male crabs weigh 110 grams for males and 130 grams or more for females. The blue crab mating was performed after the female crab was shelled and the new shell had not yet hardened. Before the female crab is about to have a pod, the male crab is guarded by the female crab. About one hour after the female crabs were husked, the male crabs mate with them immediately. Female crabs open their abdomens and expose a pair of genital holes on the sternum. The male crab's transfer device is inserted into the female's genital hole for mating. The mating time usually lasts 2-3 days. After the mating is completed, the male crab also waits for the female crab for a period of time to prevent other crabs from invading until the female crab shell completely hardens. Usually blue crabs mate with one sperm for spawning twice. Whether the male and female blue crabs mate or not is easily discerned by the naked eye. The main difference is that the mated male and female crabs have many cracks in their abdomens, which is caused by the wear and tear during mating. Female crabs that have been mated, have open bristly burrows around the abdomen, and can see that the genital hole has been plugged by the fallopian tube's secretions. The center of the junction between the posterior edge of the cephalothorax and the abdominal segment can be observed. The milky white dots with the size of the soy bean can be seen with light pressure. The mated female crabs were dissected and showed that the seminal vesicles were obviously enlarged and the holes were white. Microscopic examination showed sperm. Green crabs spawn in the blue crab ponds along the coast of the South China Sea. They can cultivate ovaries rich in female crabs, commonly known as crabs. This kind of crab is rich in food, suitable in temperature and salinity, and has been elicited after measures such as removing the eye shank. It is intensively cultivated for about one week. The blue crab will spawn on its own and hold the eggs on the abdomen bristles. The amount of eggs held by female crabs is related to their maturity, constitution, and environment. Under normal circumstances, female crabs spawn at night. There are also some spawning in the afternoon, this is an abnormal time spawning, the majority of spawning is small, after the majority of spawning fell to the bottom of the pool, it is not easy to adhere the eggs on the bristles of the abdomen, like abortion. The normal spawning of the female crab is at the bottom of the pool, and the ventral segment expands into a horizontal shape, and quickly adheres to the abdomen bristles after spawning. According to the author's observation, the amount of spawning of blue crab varies from place to place. In addition, there is usually a positive correlation with body weight, and the individual has a large amount of fecundity. In general, the amount of eggs per one animal is between 100 and 4 million. Female crabs with a body weight of 250-500 g have strong physique, high egg holding rate, high hatching rate, and good nursery effect. It is better to choose such female crabs for artificial breeding. The developmental speed of embryonic development of green crabs is closely related to the temperature of the water, which is the problem of accumulated temperature, that is, within a suitable temperature range, the water temperature is high and hatching is fast, and vice versa, the water temperature is 20-30°C. The optimum water temperature is 25-30°C. When the water temperature exceeds 32°C, the embryonic development is affected, often with many dead embryos, and the development time is also prolonged, resulting in diapause. Green crab fertilized eggs will undergo a series of changes along with the embryonic development color. Freshly produced eggs are orange, and the color change process is as follows: orange → light yellow → light gray → brown black → gray black → black → hatch. At the same time, as the embryo develops, the size of the embryonic body increases, and the abdominal segment gradually expands (is not easily closed). When the hatching female is to be hatched, the abdomen is stretched to a nearly horizontal state. When the embryo develops to grayish black, the heart of the embryonic body pulsates more than 100 times per minute, indicating that the embryo can hatch within 1-2 days. Green crab hatching and larval development Green crabs normally hatch from 06:00 to 08:00 in the morning. Individual crabs hatch at other times, but their larvae are of poor quality. Robust crabs often hatch while swimming. Weakly hovering crabs, often lying on the bottom of the pool or on the walls of the pool, swing their appendages and hatch hatchlings. The incubation time usually ends in about 20 minutes. The rapid hatching time and short time indicate that the embryonic development is synchronized and the hatched larvae are more robust. After hatching, the sturdy larvae immediately go up and the clusters become dark. From the intensity of phototaxis, it is possible to identify whether the larvae are robust or not. For artificial seedlings, we must choose strong and strong larvae and eliminate weak larvae. The newly hatched larvae were stage I larvae, which passed through the pupa larvae five times, divided into five stages, then metamorphosed into big nymphs, and then metamorphosed into juvenile crabs after molting. Its growth rate is directly proportional to water temperature. The hatching time at 28-30°C and the development time of bigeye larvae was 16-18 days, and it took 21-24 days to develop into larvae. Juvenile breeding techniques Blue crab nursery ponds can be used or properly remodeled, preferably a dedicated crab seedling pond, which is easy to operate. When the blue crab emerges, it will attach to the bottom of the pool. It is better to have a larger slope at the bottom of the pool and it is easy to emerge. The density of the larvae should be properly sparse, usually 5-10 million larvae per cubic meter of water. If the density is too large, it will unfavorably increase the survival rate. Because the early bait is not easy to solve, there are also people who claim that early-stage fostering should be followed by appropriate sparseness in the middle and later stages. However, sparse work sometimes also damages the larvae and has an impact on the survival rate. During the first phase of the larval larval newly hatched by blue crabs, they are immediately fed with bait. The open bait is a small plankton, usually a larvae of Chlorella, Platymonas, rotifers, shellfish, or carapace. The nauplii of the class. With the development of larvae, the zooplankton has gradually changed to small zooplankton as the main bait, such as Artemia larvae, branches and feet, scratching feet and so on. When the larvae develop into large ocular larvae, they gradually become carnivorous. At this time, it is necessary to control the feeding amount, otherwise the water quality is easily corrupted and the nursery fails. In the artificial nursery there are enough live feeds that are the key to success. The nursery process should be inflated. The aeration rate is similar to that of the shrimp seedlings. The amount of aeration in the early stage is small, and then it is gradually increased, so that the dissolved oxygen in the water is maintained at 5 ml/liter or more. Water larvae cultivated, pH 7.8-8.8. Salinity 25-32 ‰, larvae tend to fade in the later period, to the big eye larvae can gradually reduce the salinity, promote its better growth. In the early period of seedlings, water can be added, and in the middle and later periods, the water should be changed appropriately. In particular, it is easy to pollute the water, and the amount of water to be changed must be increased by more than 50% per day. When the blue crab larvae develop into the big eye larvae, large chelonians have developed and their ability to displace can be strengthened. When the food is insufficient or the feed is not suitable, they will eat each other. Especially when the larvae molt, the mutual danger of residual food is greater. Therefore, at this time, putting some concealed substances in the nursery ponds properly can reduce mutual disability and improve the survival rate of nursery. Disease control during nursery period Blue crabs often have bacterial diseases during the nursery period. Vibriosis and vibriosis are common. There are fungal diseases such as chytridomycosis, and ciliate spurs. The fixed ciliate disease is commonly polypene, and there are many organic substances in the water during the rearing period, and it is easy for polypenesis to occur. Keeping water clean is an effective measure for prevention. These disease prevention measures can be made by referring to the method of raising shrimp. The artificially raised seedlings of the blue crab grow quickly. The author tried several times to raise the effect very well. The male crab can grow to 340 grams in 93 days and the male crab can grow to 575 grams in 180 days (winter). Each female is 300-400 grams. After the artificial crab seedlings can supply a large amount of market, it will promote the development of the Qingjie aquaculture industry. Generally from juveniles with large eye larvae to larvae with a shell width of 2-3 cm, the survival rate is about 90%. There is a 95% survival rate of 3 to 9 centimeters in width of the crabs and 3 centimeters in the shell. This large crab is quite deducted and can be stocked. Artificial crab seedlings will certainly replace natural crabs in the near future.
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