Several key factors that should be paid attention to in healthy culture of Japanese scallop

Since the 1980s, floating raft culture of Japanese scallop has developed rapidly in Changhai County, Liaoning Province. At present, the culture area has reached more than 100000 mu, and it has become an important species of local famous and special mariculture, which plays a very important role in the development of marine fishery economy. Although the culture technology of Japanese scallop has been popularized rapidly, due to the negligence of some technical links in the operation, the mortality rate increased continuously during the culture period, and the specification, quality and fatness of commercial scallop decreased, thus affecting the economic benefits of the industry. Based on many years of investigation and on-the-spot investigation, the author analyzes many problems existing in the current culture of Japanese scallop, and thinks that the key problem for the sustainable and healthy development of this industry is to pay attention to popularizing the healthy culture model of Japanese scallop.

1. The main problems in the culture of Japanese scallop.

1. The layout of culture floating raft is too dense. From the point of view of the layout of floating raft at sea, the distance between floating raft is about 5m. Driven by interests, some farmers set up floating rafts in the existing rafts, and some blocked almost all the flow channels and waterways between different rows in order to increase the length of the raft, and the floating rafts on the sea were of different length and extremely irregular. The short one is about 70m, and the elderly is even about 200m. One floating raft is equivalent to the shellfish hanging number of the past two floating rafts, which not only affects the normal flow of sea water, but also blocks the waterway. And buried a security risk.

two。 The stocking density of seedlings is too high. The phenomenon of large-scale death has occurred in the culture of Japanese scallop in Changhai County since 1984. after years of investigation and research by experts, many reasons have been analyzed, such as the culture capacity is too large, the primary productivity of the culture area has reached the limit, and so on. We should be soberly aware that the carrying capacity of the sea area is limited. At present, the use of culture cages are basically in 15-20-layer plates, but the seedling density of shrimp-Japanese scallop in each layer has reached about 300 from the third-level temporary culture, and the overwintering temporary culture density is also nearly 100. This practice of blindly increasing the stocking density not only affects the individual growth rate and product quality of Japanese scallop, but also easily leads to the death of shellfish seedlings and the increase of deformed shellfish, which increases the mortality rate of shellfish seedlings. It reduces the fatness of commercial shellfish. Once the pollution of the sea area is caused, the loss will be even heavier.

3. The breed of culture is single. A few years ago, shellfish culture was mainly chlamys farreri or bay scallop. After the death of the two major varieties mentioned above, they now turn to the culture of a single variety of Japanese scallop, but once there are problems in the culture of Japanese scallop, there are no other alternative varieties to supplement. This single-species culture method is disadvantageous to the future development of farmers. According to the investigation, the chlamys farreri and bay scallop from individual farmers are growing satisfactorily this year, so in the absence of new alternative varieties, it is possible to culture shrimp scallop, chlamys farreri, bay scallop and other species at the same time.

4. The danger of death of shrimp and Japanese scallop still exists. The artificial breeding and floating raft culture of Japanese scallop in Changhai County are affected by the high temperature above 23 ℃ in summer, and the seedling preservation rate has been very low, which can not form a scale for a long time. In recent years, due to the change of natural environment and the improvement of culture methods, the survival rate of shellfish seedlings has been improved. We compared the water temperature in some aquaculture areas of the county from 1999 to 2004, and found that the summer water temperature before 2000 was different from that in recent 2 years. For example, the highest water temperature reached 24 ℃ ~ 26 ℃ from August to September in 1999, while the highest water temperature from August to September in 2003 and 2004 was only about 23 ℃. After comparative analysis, it was concluded that the main reason for the increase of survival rate of Japanese scallop in recent years was that the water temperature was relatively low. Therefore, it is suggested that when transporting shellfish seedlings, farmers should pay special attention to the temperature difference between different places and the methods of transporting shellfish seedlings, so as to avoid weakening the resistance of shellfish seedlings due to the excessive temperature difference between the two places, raising shellfish seedlings in an unsuitable environment, and so on.

Second, several key factors that must be paid attention to

1. Seize the season with suitable temperature and cultivate seedlings as early as possible. Chlamys farreri is a kind of cold water shellfish. The suitable temperature for growth is 5 ℃ ~ 20 ℃, and the optimum water temperature is 10 ℃ ~ 15 ℃. In the range of suitable temperature, the metabolism of scallop is exuberant, which plays a positive role in respiration and excretion, exercise and feeding, digestion and growth, gonadal development and reproduction. Therefore, when the water temperature is above 5 ℃ and below 20 ℃, the seedlings should be divided and cultivated as soon as possible, and the rapid growth period can be entered in time after slow seedling.

two。 Change the shoreline seedling into the sea seedling in order to shorten the dehydration time. The shellfish seedlings are transported from the temporary raft to the shore, and then to the raft area. The round-trip transportation time is long, and it is easy to cause the shellfish seedlings to be dehydrated for a long time, and the water temperature on the shore is high and is impacted by wind and waves. Sand and impurities on the shore are easy to enter the shell of shellfish seedlings, which has a great impact on the growth of shellfish seedlings. Seedling at sea is to put shellfish seedlings into the sea while dividing seedlings, which greatly shortens the dehydration time of shellfish seedlings, and its mantle is not easily affected. The practice shows that the operation of dividing seedlings at sea can not only improve the survival rate of seedlings, but also be more beneficial to the normal growth and development of shellfish seedlings.

3. Clean the net cage in time to remove impurities and prevent shellfish seedling pollution. The used cage should be cleaned before loading the seedlings to remove impurities; the new cage should be soaked in sea water before use; the old and seriously polluted cage or the new cage with odor can not be installed directly to prevent the pollution of shellfish seedlings. In addition, the dead shell and impurities should be removed when dividing the seedlings, so as not to pollute the water body and cause a vicious circle.

4. Choose a suitable temporary rearing area. The seedling of Japanese scallop has strict requirements on the temporary culture sea area, with large wind and waves and rapid running water, so it is not suitable for temporary culture of shellfish seedlings with poor drainage, large floating mud and poor bait organisms, which is also not conducive to the growth of shellfish seedlings. Qualified farmers should choose the deep-water area with slow water flow, great transparency, less floating mud, no big waves and rich food organisms to temporarily raise shellfish seedlings to create a good growth environment for shrimp and Japanese scallop seedlings. The selection of suitable temporary culture area is the preferred condition for cultivating seedlings with strong physique and vitality.

5. Make rational use of the aquaculture area and clean up the illegally occupied raft area waterways or waterways. The spacing between rows shall not be less than 60m to ensure smooth flow in the raft area and reasonable arrangement of floating rafts.

6. Increase the distance between the rafts. The farmers shall adjust the additional floating rafts between the rafts, the distance between the rafts shall not be less than 8m, and the floating rafts shall be reasonably arranged within the scope of use of the sea area.

7. The number of hangers should be reasonable. The hanging quantity should be arranged reasonably according to the current condition and safety degree of the sea area, and the distance between breeding cages should not be less than 1m.

8. The stocking density of seedlings should be suitable. There shall be no more than 100 seedlings per layer for the third-grade temporary culture, 40 seedlings per layer for overwintering cultivation, 20 seedlings per layer for one-year-old shellfish culture, and 13 seedlings per layer for large adult shellfish culture.

9. Strengthen law enforcement, even if correct the unscientific illegal operation phenomenon, protect the ecological environment of the aquaculture area from the overall situation, reduce the pollution of the sea area, in order to improve the survival rate of seedlings and promote the rapid growth of seedlings.

10. We will continue to implement a healthy aquaculture model and maintain the ecological balance of the water area. Disease and death still threaten the culture of Japanese scallop, and prevention and control should be the main way to prevent the disease. at the same time, in view of the current situation that the water quality of cultured waters is polluted and the water body approaches and reaches the degree of eutrophication, we should continue to study and popularize the economic species suitable for local growth. from single-variety culture to the combination of multi-variety shellfish and algae culture.

11. Keep strict precautions during high temperature to ensure the safety of seedlings in summer. In recent years, because the summer water temperature is lower than that in previous years, people almost forget the seedling culture method of sinking raft in deep water layer to prevent high temperature, and ignore the fact that the culture of Japanese scallop is limited by high temperature. therefore, farmers should adjust the stocking water layer of Japanese scallop in time according to the changes of water temperature in their respective culture areas, and when the water temperature reaches 23 ℃ from August to September in summer, measures should be taken as soon as possible. The floating raft is controlled to a low temperature with a water depth of less than 7m with a movable float to ensure that the shellfish seedlings spend the summer safely.