How to improve the survival rate of scallop seedlings in cultured scallop

The ponds and ponds suitable for seedling conservation should have an east-west rectangular structure, sand bottom or hard bottom, with a water storage depth of more than 1.5 meters, a salinity of less than 35 ‰, and no pollution of open sea water sources; before entering the pond, it is necessary to thoroughly remove the bottom dirt layer and give full exposure; it is forbidden to put large-size benthic fish or other species that require a large amount of bait in the seedling ponds to prevent water pollution.

Pay attention to the regulation and control of water quality. 10-15 days before entering the pond, the water intake of scallop is 60cm-80cm, fertilizing and fertilizing water, the amount of nitrogen fertilizer per cubic meter of water is 3.5g, the application rate of phosphorus fertilizer depends on the situation, it is generally about 10 times of nitrogen fertilizer, and the bait density is controlled at 50, 000-200000 / ml. 4-5 days before entering the seedling, the pool water is gradually added to the highest water level, with a transparency of 70 cm-80 cm; if the transparency is too large, when the temperature is high around noon, the method of less dosage is used to apply inorganic fertilizer in time; if the transparency is too small, the bait density is too large, a few days before the scallop seedlings enter the pool, the amount of water should be appropriately increased, so that the water quality is clear but not thin, fat but not old. Before seedling release, the physical and chemical indexes of the water quality of the seedling protection pond should be strictly monitored to ensure that the indicators are within the prescribed range; after the seedling is distributed, the daily water exchange volume should reach more than 20%, and if the water color changes to water quality aging, it is a sign of the death of shellfish seedlings. At this time, the water should be changed thoroughly or the pool should be changed in time to protect the seedlings.

When selecting high-quality juvenile shellfish seedlings out of the warehouse, we should carefully select the juvenile shellfish seedlings with uniform specifications, firm adhesion, suitable density and attachment time of less than 15 days. The water quality condition of the seedling farm should be basically the same as that of the seedling preservation pond. generally, the water temperature of the pond is stable at 13 ℃, and the water temperature of larva cultivation should not be higher than the prescribed water temperature. In raising seedlings, the food varieties of unicellular algae should be matched reasonably, and the supply should be sufficient to ensure uniform specifications and healthy health.

In general, the specification of juvenile shellfish is 500 microns, and the specification is raised to 700 microns-800 microns, which can greatly improve the seedling preservation rate.

Strict operation rules for loading and transporting seedlings bagging personnel should carry out pre-post technical training, operate skillfully, shorten the bagging time as much as possible, and hoist the adhesive base to the mouth of the bag with polyethylene thread to avoid multi-layer stacking and backlog friction, resulting in injured seedlings. It is suitable to transport seedlings in the early morning or at night. During transportation, attention should be paid to sealing, moisturizing and cooling, so as to shorten the transportation time as much as possible.

It is reasonably determined that the seedling density can be protected by no more than 100 million young shellfish per mu and no more than 30,000 seedlings per bag. With the increase of the specification of juvenile shellfish, the number of loaded seedlings should be reduced appropriately.

Use double-layer net bags and round net bags to protect seedlings

When the seedlings are protected in double-layer mesh bags, the juvenile shellfish are loaded into polyethylene mesh bags with specifications of 20-30 mesh and a cover of 40-60 mesh. About 10 days after entering the pool, the shellfish seedlings in the bag have grown up, the outer bag will be removed, and the young shellfish on the outside of the inner bag will be temporarily reared in a 40-mesh bag, which can not only remove the attachments, but also evacuate the shellfish seedlings. The seedling preservation rate of double-layer net bags can generally reach more than 30%.

The round mesh bag is made of 20 mesh and 40 mesh polyethylene mesh, with a diameter of 200 mm and a height of 280 mm-300 mm at the bottom, with a cylindrical plastic frame with a diameter of 185 mm and a height of 60 mm. The circular mesh bag has many advantages. Under the support of the plastic frame, it has a large space for seedling protection, and the flow of water is smooth, so that the shellfish seedlings can move freely, increase the feeding probability, and avoid the death caused by the accumulation, friction and mutual bite of juvenile bain. the seedling preservation rate of circular mesh bags can be as high as 40%.

Strengthen the daily supervision measures to fully tighten the float, appropriately increase the falling stone of the seedling bag, reduce the swing of the net bag, persist in patrolling the pool, and prevent the occurrence of entanglement and breaking of the net bag, broken rope and falling stone, as long as the mesh is not seriously blocked, there is no need to brush the net. When it is necessary to wash, it can be lifted in water to reduce the damage of shellfish seedlings.

At the right time, the time for seedling protection in the pond should not be too long, generally 20-25 days, the specification of juvenile shellfish reaches about 3 mm, then the seedlings can be divided into the sea and transferred to the middle breeding stage. The time to go to sea should be in calm weather to avoid dryness and direct sunlight. It is better to carry out in the morning and evening.