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(1) Selection conditions for farms

For clam farms, the wind and waves should be relatively calm. , medium and low tide areas with smooth tides, flat terrain, lots of sand and little mud (sand content is 70% to 90%); the specific gravity of seawater is 1.010~l.025, and the ideal specific gravity is 1.012~1.020; the flow rate is 40~ 100 cm/sec.

(2) Sowing seedlings throughout the whole city

1. Seedling sowing season: The seedling sowing season varies greatly depending on the individual size of the seedlings. White seedlings are usually sown in April to May; medium seedlings are mostly sown in December, and in some places the seedlings are postponed to the following spring due to cold weather and other reasons; large seedlings are generally sown before spawning.

2. Renovation of the cheng: The main work of reorganizing the cheng is to build embankments with miscanthus at the edge of the chengdi near the harbor road and the subtidal zone to prevent the loss of clam seedlings. The embankment is 30 to 40 centimeters wide and about 25 centimeters high. Large tidal flats should also be surrounded by miscanthus and divided into several blocks to facilitate management. Then the stones and debris on the cheng surface were picked up, the depressions were filled with sand, and the cheng surface was leveled. If the site is soft, drainage ditches must be dug to prevent water accumulation in the site. Finally, one week before sowing seedlings, sprinkle the field with bleaching powder (15 kg/acre) or tea seed cake (8 kg/acre) to kill harmful organisms.

3. Seedling sowing methods: There are two seedling sowing methods: dry sowing and wet sowing.

(1) Dry sowing: When the field is dry after low tide, the clam seedlings are unloaded from the seedling transport boat moored on the field. When sowing seedlings, it is required to spread them evenly to prevent them from gathering in piles. If the tide has risen and it is impossible to continue sowing seedlings or if sowing is not completed, the clam seedlings should be removed and immersed in the water until the next tide.

Because white seedlings are small and light, they are easily carried away by the tide and lost, so this method is often used to sow seedlings.

(2) Wet sowing: In wet sowing, when the tide has not left the cheng surface, the clam seedlings are transported by boat to the cheng ground where the signs have been inserted, and they are spread evenly within the marked area according to the amount. Sowing of seedlings should be carried out during flat tide or slow current to avoid loss of clam seedlings.

The wet sowing method increases the time for sowing seedlings, improves work efficiency and the survival rate of clam seedlings, but the sowing is less uniform. This method is only suitable for sowing medium and large seedlings.

4. Seedling density: Seedling density directly affects the growth rate and yield of clams. If the seedling density is too high, the clams will grow slowly; if the seedling density is too sparse, the cultivation area cannot be fully utilized and the yield per unit area will be low. Therefore, it is necessary to master the appropriate seeding density. The amount of seedlings sown should be determined according to factors such as the size of individual clam seedlings, the height of the tidal area, and substrate conditions (Table 19-6): Large clam seedlings have a high survival rate and can be sown less; those in low tidal areas , the clam seedlings take a long time to feed, grow quickly, and have many enemies. The clam seedlings have a high damage rate, so they should be sown more appropriately; in the fields with hard substrate and good stability, they can also be sown more.

In addition, it should be increased or decreased according to the amount of bait organisms in the sea area and the flow rate.