Control of several key points in large size "Yellow River Estuary" hairy crab culture

In order to start the "Yellow River Estuary" aquatic product brand and improve the market competitiveness of the "Yellow River Estuary" hairy crab, Kenli County, Shandong Province, conducted a large scale "Yellow River Estuary" hairy crab culture experiment in the 10,000 mu River Crab demonstration Park in 2005, and achieved good economic and social benefits. Now several key technical issues in the process of culture are discussed with the majority of colleagues.

I. Pond ecology

Under the influence of traditional ideas, many units use the method of building ponds and raising, but the effect is not good. The survival rate of hairy crabs in the Yellow River Estuary is low, the market size is small, and the economic benefit is poor. This is because: ① underwater effective area is small, water utilization rate is low; ② water quality is difficult to manage, "Yellow River Estuary" hairy crab growth, molting in the weight rate is low; there are no attachments and concealment in the ③ pond, "Yellow River estuary" hairy crab has high drilling rate, easy to escape, more opportunities to kill, and vulnerable to enemy attacks; under the condition of low dissolved oxygen in ④, the organic matter at the bottom of the pool is decomposed to produce toxic gases, invade the crab body, and affect the meat taste.

The living habits of hairy crabs in the Yellow River Estuary are different from those of fish, requiring different ecological conditions. It requires waters with high coverage of aquatic plants, shallow but unpolluted silt bottom, pH7.5~8.5, as well as clean water quality and suitable water depth. Soil and water sources are generally determined, and appropriate water depth and pH are also easy to control, but as important ecological factors, aquatic plants have different ecological functions due to their different varieties and cultivation forms. Such as: verticillium verticillata, bitter grass, goldfish algae, etc., "Yellow River Estuary" hairy crabs like to eat, but can not form a stable community, so it is difficult to form an effective ecological effect; water peanuts can form a stable community, but it pollutes the water as heavily as cattail grass; the roots of Zizania caduciflora are well developed, and the young buds and tender stems are the happy event of hairy crabs in the "Yellow River Estuary". They have strong regeneration ability and water purification ability, but they need to be carefully cultivated year after year in the ponds where the crabs are released earlier. Although Reed is not fond of eating hairy crabs in the Yellow River Estuary, it has a strong ability to purify water and does not pollute the water after death. The planting forms of Zizania caduciflora and Reed are strips with shallow trenches, which are easy to feed and recapture, and give a certain living space, which can ventilate and increase light. In general, the coverage rate of aquatic plants should be 70% to 80%. From an ecological point of view, the pond area is too small to create a good ecological environment; the pond area is too large, which brings difficulties to management and recapture. Therefore, the pond area should be 1 mu ~ 15 mu.

2. Crab breeding and stocking

1. The time of stocking crabs is in October of the Gregorian calendar at the earliest and June of the Gregorian calendar at the latest. In the former, many sets of crabs are placed in adult crab ponds, resulting in stump, death and mixed size when adult crabs are caught, which affects overwintering and spring management, while the latter coincides with the first molting period of hairy crabs in the "Yellow River Estuary", which not only has great transportation losses, but also delays the crab's adaptation to the new environment, and the growth starting point is low. Therefore, the release time should begin after the adult crabs were sold at the beginning of the previous year and end in mid-April. The smaller the size of the seedling, the earlier the stocking time should be.

two。 Crab species quality requirements neat specifications and achieve a certain weight, breeding in the same year can meet the 100g/ only ~ 150g/ only listed specifications. According to the author's determination, the molting weight gain rate in adult crab culture is 47.3%, and the good one is 61.3%. From April to September, the minimum molting time is 2 times, and the maximum molting time is 4 times. Considering the accumulated weight gain rate of non-molting growth, the molting weight gain rate of 4 times is 80%. If only 100g/ is required to be listed, the minimum specification of crab species should not be less than 52g/. As far as the general culture level is concerned, the molting growth and weight gain rate is between 50% and 60%, and the crab species specification is 40 / kg~80 / kg. Secondly, the size of artificially cultivated young crabs is smaller than that of natural crabs, and a considerable number of them reached sexual maturity in that year, and the weight of biological individuals decreased significantly. On the one hand, there is still incompatibility between artificial breeding techniques and the requirements of river crab development; on the other hand, there is a serious degradation of river crab germplasm, and the mortality rate of sexually mature individuals molting for the first time in spring is more than 60%. Therefore, the selection and purchase of crab species should not only pay attention to specifications, but also select improved varieties, and check sexual maturity and individual proportion at the same time.

3. When the stocking time of density crab is before the middle of April, the coverage rate of aquatic plants in the pond accounts for 80%, its effective area can reach 100% to 150%, the silt is shallow but not dirty, the specification of crab species is 40 / kg, the stocking density is 1.5 / square meter ~ 2.0 / square meter, and the culture survival rate is 85% and 90%. Crab species specification 60 / kg, stocking density 2.0m ~ 3.0m ~ 2, culture survival rate 80% ~ 90%, crab species specification 80 / kg, stocking density 3.0m ~ 4.0m ~ 2, culture survival rate 75% / m ~ 800 Crab species specification 100s / kg, stocking density 4.0ind / m2, culture survival rate 70%-80%, stocking density can also be increased or decreased according to the quality of the conditions.

III. Feed

The "Huanghe Estuary" hairy crab has a wide diet and strong food selection, so the continuous feeding of single variety feed has many disadvantages: the nutrition of ① is single, the growth of crab body is slow, the feed utilization rate of ② is low and the coefficient is high, and ③ pollution is serious, which spoils the water quality. Through the experimental comparison, the selectivity of the "Yellow River Estuary" hairy crab was stronger than that of the single ingredient feed prepared with the mixture of high-grade and low-grade raw materials, the feed coefficient decreased obviously and the crab body grew faster. At the same time, in the case of commercial feed, the "Yellow River Estuary" hairy crab still needs to eat a certain amount of aquatic plants, so no matter how sufficient the concentrate feed is, it should be properly fed to some aquatic plants.

IV. Management

1. The management of crab culture during molting period is better, the molting peak period is 10 days, and some take 20 ~ 30 days. Obviously, the long molting period is not conducive to weight gain and cultivation. As for the protection of soft-shell crabs, the measures can only be shown in the management of the molting process. To make the "Huanghe Estuary" hairy crab concentrate on molting, the key points include: ① accurately controls the time of each molting; before and after each molting of ②, the nutrients such as animal protein in the feed should reach 50% to 80%; once the molting crab is found in ③, it will sprinkle quicklime 15kg/ mu ~ 20kg/ mu, at the same time, add a large amount of water, change water, and make the new water level higher than the original water level 10cm, in order to increase the area of attachment. After ④ molting enters the peak period, only water injection does not need to change water; during the peak period of ⑤, the number of feed tables should be increased to ensure the full intake of soft-shell crabs. After molting, the soft-shell crab hardens after about 2 days, but it takes 10 days to raise it indoors. Practice has proved that the intensity of light has a great influence on the hardening of soft shell, so it is difficult to plant shady trees on the ridge of the pond.

two。 The temperature difference between day and night in early spring is large. Because the hairy crab "Huanghe Estuary" is sensitive to temperature, it comes out of the water when the water temperature reaches more than 7 ℃ in the afternoon, and when the temperature gradually drops to 2 ℃ at night, the foot is stiff, and the phenomenon of "love ridge" appears as in late autumn and early winter. Therefore, sooner or later, we should persist in patrolling the pond and put the frozen "Yellow River estuary" hairy crab in warm water of about 20 ℃, which can return to normal. Feed a small amount of high-quality feed in time. Adult crabs stored in the pond should be sold in time, otherwise it is easy to mate and die when the water temperature reaches more than 13 ℃. Individuals whose small size cannot be listed and whose gonads are mature should be cultured separately until the end of the first molting, when the gonads have degenerated to the Ⅲ-Ⅰ stage. It is necessary to clear ponds, clear silt, remove weeds and apply calcium fertilizer in time.

3. Summer management to control the amount of feed, feed should not be excessive. Pay attention to the change of water quality to prevent the production of toxic gases at the bottom of the pool. Regular use of microbial preparations or substrate modifiers to improve water quality, can also be regularly applied with quicklime, regular change of water. Prevent crabs from escaping during the flood season.