Death causes and preventive measures of cultured scallop

1 cause of death

1.1 excessive aquaculture density is a common problem. Farmers one-sidedly pursue the yield per unit area, and most of them adopt the method of high-density culture, with 100 UV 120 seedlings per layer net cage, or even higher. At present, scallop culture methods are mostly vertical, the water exchange capacity is poor, a large number of excreta can not be diffused in time, deposited on the seafloor around the culture raft, and decay, resulting in harmful substances (such as H2S). When the wind and waves increase, these harmful substances rise and poison the scallops. On the other hand, too high culture density led to a sharp decrease in food organisms, scallop due to the lack of bait, disease resistance and environmental deterioration ability to decline, resulting in a large number of death of scallop.

1.2 winds and waves affect many typhoons in the Zhejiang sea area, and they are concentrated in August-October, when the scallop lacks foot silk. Due to the impact of the wind and waves, the scallops rolled, collided and stranded each other in the cage, resulting in injury and death.

1.3 effect of reproduction due to the fact that at present, most of the seedlings of scallop come from artificial breeding plants, the seedling stage is early, the growth time is long in the sea area, and the gonads can develop and mature in August and September, and the organic matter and energy used for growth are reduced at this time. So the physique of scallop is relatively poor. When the "autumn tiger" weather occurs in the Zhejiang sea area, the water temperature in the shallow sea area changes greatly, resulting in the death of a large number of scallops. In our survey, we found that larger individuals with well-developed gonads had a higher mortality rate.

1.4 Sea area pollution due to the discharge of urban sewage and the increase of dumping objects from wharves and ships, the sea area is increasingly polluted, some culture areas have low transparency and a large amount of oil pollution, resulting in the deterioration of water quality and high mortality of scallops.

2 Preventive measures

2.l before adopting appropriate culture density, the appropriate culture density should be selected according to the flow rate of sea area, the transparency of water body, the quantity of bait organisms, the quality of seedlings, the level of culture and so on. The suitable size of 1cm seedlings should be 60 eggs per layer. When the seedlings reach 2-3cm, the seedlings should be divided in time and 20 eggs per layer should be released, and a reasonable culture layout should be designed to keep the cage spacing 60-80cm.

2.2 strengthen cultivation management during the period of culture (especially during the typhoon season), the safety of culture facilities should be regularly checked; the attached organisms on floating mud, net cages and shells should be removed in time, and the dissolved oxygen and bait organisms in the water should be fully utilized.

2.3 timely adjustment of aquaculture water layer can be controlled at about 3m in peacetime. During the period of high temperature in summer, typhoon season and large temperature difference in summer and autumn, sink 1m in the same cage and fasten the attached rock, or move to the outer area with deeper water for culture.

2.4 implement interculture and rotational culture of shellfish and algae to create an excellent ecological environment the photosynthesis of algae can increase the content of dissolved oxygen in water and improve the growth environment of scallop, while the excreta of scallop can provide nutrients for algae growth; at the same time, it makes full use of the culture space and improves the comprehensive economic benefits.