The sea-scallop seedling maintenance rate of the bay scallops is generally less than 10%, but in the shrimp ponds, the seedling conservation rate is generally above 1.0%, and even the higher ones can reach 40% or more. Due to different management and methods, the seedling maintenance rate is very poor. Great disparity. According to the production and test conditions in recent years, several technical points that should be noted for the preservation of seedlings in the bay scallops are described below.
1. Pond Condition The pond is better with sandy bottom, followed by rock reefs, with poor sand quality, and poor mud bottom quality. It should be able to maintain a water level of about 1.0m below the bottom of the pool. The shrimp ponds in the north all have a ring ditch, and the water level of the ring ditch can be maintained above 1.3 m. Before harvesting shrimp, it is best to turn the bottom of the pool to the bottom of the soil. Sprinkle lime 50-100kg per acre evenly to improve the bottom quality; install 50-60 mesh nylon screen at the inlet.
2. Fertilizer Before the juveniles are out of the pond, the shrimps have already been stocked, and the residual bait of the shrimps and the excretion of the shrimps, together with the consumption of the shrimps by the zooplankton, can achieve the purpose of water and fertilizer. It is still relatively large. Apply 1ppm of nitrogen fertilizer every 2 days and apply 2-3 times. If fertilizer and water are difficult, it can be used for fertilization once a day for 5 days. With good water, the growth rate of scallops can be increased, and the survival rate and seedling maintenance rate are also improved. Generally, the transparency of the pool water is about 40cm, the water color is yellow-brown, yellow-green, and the food predominant species are Chaetoceros, diamond-shaped algae, Skeletonema, Cylindroa, and Chlorella. If there is too much dinoflagellate, Timely change the water or replace the pond.
3. The juveniles are out of the pool Currently, the bay-out scallop outfall specifications are generally controlled at about 250 μm. The mesh of the seedling-bags should be used for 80 mesh, and the mesh bag size should be 25cm40cm-30cm50cm. The effect of the mesh bags is too small. Bag density is 20,000 to 10,000 bags per bag. A mesh or brown rope must be added to the bag to increase the adhesion matrix and to meet the growing demand of juveniles. A hard nylon net is also added to facilitate picking. The bag is stretched to increase the environment inside the bag, and at the same time, the surface area of ​​the seedling bag is also increased, and the exchange capacity of the water body inside and outside the bag is enhanced. The floating raft should be set in the ring ditch. The raft should be about 20m long. The two ends should be fixed by wooden stakes. The buoyancy should be dense and evenly set. The seedlings should be hung in the low light water layer of 30-.40cm. Each string of 4-6 bags, hanging spacing 50cm, each string under a 0.7-1kg falling stone, the Department of buoyancy should be floating surface 1/3 or more.
4. Brush bag and bag hanging bag. Do not wash the bag within 5 days to prevent the larvae from leaking from the mesh. During the holding period, the daily growth of the shell is generally about 1.0 μm, so the general shell height can reach 300 μm after 5 days, while the 80 mesh nylon mesh has an aperture of 198 μm, and the hypotenuse of the aperture is 280 μm, so it is safe to brush the bag without Leaving baby boy.
Brush bag is best to use a large test tube brush or long hair hard brush, one to wash the mud on the bag completely clean; the second is to plug the debris mesh hole to improve the exchange of water inside and outside the seedling bag, the traditional The soft brush used light brush, light wash, it is difficult to brush through the mesh, which is currently the shrimp pond seedling operation is too careful, resulting in poor water exchange within the seedling bag, bait and dissolved oxygen is difficult to reach the scallop larvae The main reason for the corresponding reduction in the seedling maintenance rate is the demand. Brushing the seedling bag must be done once a day. Many units are used once a day for 3 days. This is absolutely negligible because the mesh hole is too small and the pool is free of wind and waves. It is easy to plug the mesh. After about 13 days of storage in the 80-mesh bag, it should be poured into a 60-mesh bag. The mesh size of the 60-mesh sieve is 258 μm, and the length of the mesh is 365 μm. The scallop shell height is above 360 ​​μm. Each bag can hold about 10,000 capsules; after being raised for 10 days, the larvae of scallops are already over 500μm, and they should be poured into 40-mesh bags in time, about 5000 bags per bag. All kinds of mesh bags must be made of hard nylon mesh bags. And add a certain amount of attachment groups. When using a 60-mesh bag, you can brush the bag once every two days, but you have to smash the bag once a day. When using a 40-mesh bag, you can hit the bag once in the water every day. You can not brush the bag.
5. Pool water management Shrimp pool water change, from the third day of juveniles into the pool, once a day early, changing the amount of water to 10% is appropriate, in the middle and late period, about 20% is appropriate. Changing the water can not only prevent water quality from aging, but also maintain a relatively stable water temperature. It can also form water flow and promote the exchange of water in the seedling bag. According to the weather conditions, in the rainy days, the pond water level should be increased as much as possible, and the seedling bags should be reduced to prevent the mutation of surface water pool salinity from causing the juveniles to adapt or even die. In the first 3 days of seedling separation, pool water exchange should be strengthened, and the amount of water exchanged can be more than 30%, so that the environmental conditions of the pool water and the water environment of the natural sea area are close to each other, so as to increase the adaptability of juveniles when they enter the sea. Improve the rate of farming into the sea.
6. When the juvenile shell is up to 1mm, the juveniles should be brushed into the seedlings in a timely manner in the water with a soft brush from the attachment base. The water in the container is changed with the brush. Sub-seedlings generally use a 30-mesh bag, each bag containing about 2000-3000 grains. The sub-seedlings are generally in June, and the temperature is relatively high. Sun-seeds should be erected or separated as soon as possible.
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