1. The choice of river
River selection is the precondition for the success or failure of river multiplication. China's domestic rivers are criss-crossing and rich in resources. The rivers suitable for the proliferation of crabs have a wide area and great potential, yet they need to be developed and utilized. The rivers that are suitable for the proliferation of river crabs should have the following characteristics: non-polluting water resources, rich natural fishery resources, gentle water flow, open rivers, many rocks in riverbeds, suitable ratios in deep water and shallow water, pH values ​​of water 6.5-8.5, and river courses The submerged aquatic plants are abundant, and many farmland and residential areas are distributed along the banks of the river.
2. The seedlings of crab species are the basis of the aquaculture industry. The proliferation of river crabs should be strictly controlled and the crabs should be put into use. The seeding time should be suitable for winter and spring. The northeast region can be postponed due to unfrozen, and it should not be postponed to the end of March at the latest; the regions in the Yangtze River basin should not be postponed until March; During the good period, the crab species should be introduced just after the Spring Festival. Because of the low temperature during this time, the young crabs are easily transported after catching and have high survival rate. The adaptability and growth period after entering the river are relatively long, which is conducive to improving the survival rate and catching rate.
The species density of river crab crabs should be increased or decreased depending on the water quality of the river and the condition of the river bed. It is generally advisable to place 100-300 crab species per hectare according to the water surface area of ​​the river during the dry season. The size of crabs introduced is generally 600-1000/kg. The seeding specifications are too small, the size of the returned crabs is not large, the seeding specifications are too large, and the cost is relatively high. According to the county's multiplication experience, the best allocation of crab species should be 600-800/kg.
In order to ensure the success of river multiplication hydrolysate and obtain good economic benefits, it is necessary to strictly control the selection of crabs, because the quality of crabs directly restricts the success or failure of river multiplication. This article highlights the following points that must be mastered in order to purchase crab species:
(1) Preferred natural crab species
The practical experience over the past few years tells us that natural crab species are superior to artificially propagated and cultivated species in terms of their survival rate and catch rate and their growth specifications. When purchasing natural crab species, it is best to directly purchase from the fishermen at the estuary in the vicinity so as to prevent the cultivation of artificially cultivated crab species as natural crab species, and to avoid the loss of the purchased species.
(2) The purchase of species depends on the physical integrity and body condition
You should purchase a crab with blue-green (original body color) and fresh luster. This kind of crab is a good product. On the other hand, if the body color is faded or slightly yellow, the quality is poor. It is necessary to remind practitioners that it is not only convenient to purchase goods in the hands of traders in farmers' markets, because the crabs have a long time to leave water and their survival rate is relatively low.
(3) Prevent the purchase of inferior crab species
When purchasing crab species, care should be taken that crab species with crab legs and abdomen umbilicus with yellow rust spots cannot be purchased. Because most of these crabs die in the river because they cannot be shelled and die, causing the proliferation costs to increase, affecting the ultimate benefits, and even causing losses.
(4) Beware of real crabs
Here, the author reminds some practitioners who do not know the physical characteristics of the crabs, should pay special attention to when purchasing crab species, if conditions permit, invited fisheries professionals or people who have the experience to buy crabs to go to buy the species to prevent some The unscrupulous species used to sell crab species such as phase-to-face crabs (commonly known as crickets) along the coast, selling species of crabs, causing serious losses to the buyers.
3. Perfecting management measures River multiplication River crabs have a large number of fishers who rely on rivers for their large water surface and long river channels. This poses great difficulties for management work. Local governments should formulate appropriate management measures according to local conditions. Here only describes the effective management method that the county has implemented for several years: that is, the combination of fishermen and non-fishermen sub-contracted rivers, ranging from 3 to 10 km each, the contractor has purchased crab species, and the fishery authorities supervised and released the crab species. Into the river. At the same time, fisheries and other law enforcement agencies cooperated with cooperative management to prevent the occurrence of illegal operations such as electricity, explosions, and poisons, vigorously promoted the fishery law, and reasonably coordinated the conflicts between fishermen's daily fishing operations and river contractors, and ensured that rivers reproduce crabs. Smooth development.
4. Timely arrest
Crabs usually grow in freshwater for about 6-18 months, and they end their splurging lifestyle. They begin to flock in groups and leave the habitat where Mr. Yuan grew up. They gather in the rivers and seas of the Tonghai River, and they arrive down the river and arrive. The estuary mates and breeds in the shallow sea. This is the reproductive migration in the life history of crabs. In fishery production, it is the annual crab cake. My county's genital migrating crabs usually start in cold dew, and gradually increase until the winter solstice. The maximum time for migrating is a few days before and after the frost fall. Because of the sudden drop in temperature, the migrating crabs enter the peak period, and the migrating time for crabs lasts for about 2 months. Therefore, practitioners should, according to local climate change conditions, prepare their own recovery crabs. The specific method for catching in our county is to select a shallow shoal where the water depth is less than lm and the water flow is gentle. Use a 2.5cm mesh polyethylene net with a net height of 2.2m. The length of the net is tailored to the width of the river. At the bottom of the river, a small wooden stake is drilled every 5m, and then the underside of the net is hung on a small stake, and the net under the river is compacted by the pebbles in the river. At the same time, along the bottom line of the net, a hole of 10cm in diameter and 1.8m in height is drilled every 8m before entering the bottom of the net. The depth of the river reaches 30cm in the river. When it is approaching the twilight moment, the river can be hung on a large stake and every other time. The 3m is stabilized by a strut. At this time, the net can be carried along with a net pocket and a pre-prepared tool for observing the bottom of the river. This crab-removing method saves time, labor, and effort. The crabs that are caught are full of limbs and have a high recovery rate. They are worth learning and promoting.
The multiplication of river crabs has been in the county for nearly a decade. This year, the rivers in our county have dropped about 150,000 large-scale crab species. The estimated production value is nearly one million yuan. The author believes that as long as the river is selected, the good crabs are planted and management measures are perfected, the ratio of input to output of river multiplication crabs can reach more than 1:10, and the comparative benefit is very significant. Compared with crabs grown in the same pool, crabs produced from rivers are large in size, fine in color, superior in quality, and taste more delicious. They are highly favored by consumers. The technical highlights of river multiplication are described below: