海州湾不同养殖区紫贻贝的营养特征及其影响因素

为探究海州湾不同养殖区紫贻贝(Mytilus galloprovincialis)收获期营养成分变化及其影响因素，于2021年1—3月测定了海州湾不同养殖区(H1：离岸1 n mile，H2：离岸3 n mile，H3：离岸7 n mile、H4：离岸13 n mile，H5：离岸21 n mile)水环境理化因子、紫贻贝的条件指数及蛋白质、脂肪、糖原、氨基酸等营养成分，分析了水体理化因子与条件指数和营养成分的关系。结果显示，随着离岸距离的增加，水温和叶绿素a (Chl-a)浓度等关键理化因子均有升高趋势，1—3月H1站位紫贻贝的条件指数逐渐增加，H2~H5站位的条件指数均在2月达到峰值；各站位的紫贻贝总糖含量呈正态分布，于2月达到峰值，其中，H4和H5站位总糖含量在3月显著下降(P<0.05)，比2月分别降低了62.7%和61.6%；H5站位紫贻贝的氨基酸含量在1月显著高于其他站位(P<0.05)，而后，在3月显著降为各站位中最低(P<0.05)；1—3月各站位紫贻贝外套膜的糖原含量呈先上升后下降的趋势，而3月H5站位紫贻贝糖原含量显著高于其他站位。本研究表明，紫贻贝营养物质储备的差异主要与水温和饵料密度有关，离岸养殖更有助于紫贻贝积累营养物质及生长，离岸养殖区紫贻贝性腺成熟早，营养物质积累快，H5站位紫贻贝比近岸站位可提早1个月上市。本研究将为拓展紫贻贝养殖空间、优化养殖布局提供数据参考。

Factors influencing the nutritional characteristics of Mytilus galloprovincialis from different culture areas in the Haizhou Bay

Mytilus galloprovincialis has high-protein and low-fat contents, as well as medicinal and therapeutical values. It is one of China''s most important mussel breeding species, with strong adaptability, mature and straightforward breeding technologies, and high yield. It mostly feeds on small plankton, with main nutrients varying seasonally with different growth stages, and the individual biochemical components of the same species also differ geographically. The change of bait is also an important factor in changing the volatile substances of this shellfish. The mussels'' nutritional flavor characteristics have been a concern of national scholars. However, the nutritional and flavor characteristics of M. galloprovincialis in different cultural areas have not been reported yet. Haizhou Bay is the main M. galloprovincialis aquaculture area in China, with an annual output of more than 150 000 tons and a value of 300 million yuan. Mussels cultivated in five sites (H1 to H5) in this region were collected once every month, from January to March. H1 is one nautical mile off the coastline; H2 is 3, H3 is 7, H4 is 13, and H5 is 21 nautical miles off the coastline. The physical and chemical factors of these water environments and the protein, fat, total sugar, and glycogen contents within the soft tissues of the sampled mussels were measured. The results showed that the M. galloprovincialis nutrient content varied among sampling time and sites and was directly related to the gonad development. The H1 condition index increased continuously from January to March, and the mussels'' highest condition index in other areas was found in February. The highest total sugar content of mussels collected in all regions was observed in February, while for the H4 and H5 areas, it decreased significantly in March and was 62.7% and 61.6% lower than that in February, respectively. These changes were mainly caused by M. galloprovincialis entering its breeding season in March. The total content of 16 amino acids and the content of flavorful amino acid at H5 were significantly higher than those in other regions in January (P<0.05). However, these amino acid levels decreased significantly and became the lowest in March for the mussels sampled in the H5 region. From January to March, the glycogen content in the mussel mantle increased firstly and then decreased, while its highest level was found in mussels collected in H5 in March. Most of the cultivated M. galloprovincialis are sold in winter. Here we observed that the gonad development and nutrients and flavor amino acids levels of the offshore mussels were different from those of the nearshore mussels, and the offshore mussel completed the material and energy storage earlier and entered the breeding period sooner, suggesting that the best marketing time is different for the studied areas. Differences in the mussels´ nutrient reserve were mainly related to temperature and feed density. The water temperature and the Chlorophyll-a (Chl-a) concentration tended to increase with the offshore distance rise, leading to the rapid development and early marketing time of M. galloprovincialis in the studied offshores. In February, mussels in the H5 area were rich in nutrients and flavor materials; therewith, they could be marketed one month earlier than in other areas. Early listing of the offshore cultured mussel can prolong its market supply time and reduce the competitive pressure caused by centralized listing. In addition, the offshore cultured mussel has a good market potential because of its short breeding cycle, wide breeding space, and good taste. In recent years, thanks to the development of internet technology, online sales have become an important sales channel in all industries. This way avoid the third-party vendor, wherein the producer can sell directly to customers with higher unit prices and a vast market. Combined with the advantages of offshore mussel cultivation, farmers can use online sales to increase their income further. With the increase in the density of offshore aquaculture in the Haizhou Bay, harmful algal blooms threaten the safety of shellfish products. Environmental problems in nearshore areas are the main factors hindering the favorable and productive development of the M. galloprovincialis industry. Therefore, the development of offshore aquaculture has great potential. Compared with the nearshore sea, the offshore sea has more extensive space, frequent water exchange, and larger environmental capacity. In order to improve the output of mussel aquaculture, New England began to transfer the aquaculture area from the nearshore to the offshore sea. Although the cost and technology needed for the offshore culture are significant, the comprehensive benefits of the offshore culture are still considerable. The offshore aquaculture development is conducive to optimizing the spatial structure of the marine industry, improving the overall efficiency of food production, alleviating its resource and environmental pressures, and cultivating new marine products with technological and industrial advantages. This study may provide supportive data for optimizing the spatial layout planning and harvesting time of M. galloprovincialis offshore cultivation.