长江安庆江段存在溯河洄游型和淡水定居型刀鲚实证研究

为了探究长江十年禁渔后安庆江段刀鲚的生境履历，利用X射线电子探针微区分析技术研究安庆江段不同类型长颌刀鲚(Coilia nasus)和短颌刀鲚的耳石Sr和Ca微化学特征。结果显示，根据耳石Sr/Ca值的变化值将安庆江段的短颌刀鲚分为2类，一类是其比值为一直小于3.0的低值，表明其纯淡水的生境履历；另一类是其比值不仅有小于3.0的低值区，还有大于3.0的高值区(小于7.0)，表明其不仅有淡水的生境履历，还有高盐度的河口半咸水生境履历。长颌刀鲚的耳石Sr/Ca值均具有小于3.0的低值区和大于3.0 (甚至大于7.0)高值区的显著波动，表现为典型的淡水、河口半咸水及海水的溯河洄游型生境履历，Sr含量面分析图谱也可印证上述结果。本研究表明，长江安庆江段刀鲚群体组成较为复杂，同时存在溯河洄游型、淡水定居型短颌刀鲚和溯河洄游型长颌刀鲚3种生态表型个体。

Coexistence of freshwater resident and anadromous Coilia nasus in the Anqing section of the Yangtze River in Anhui Province, China

The Anqing section of the Yangtze (Changjiang) River in Anhui Province, China, is one of the most important migratory routes and distribution of the highly valued diadromous estuarine tapertail anchovy Coilia nasus. In the past, this section has suffered a severe loss of C. nasus resources caused by human activities, especially overfishing and water pollution. Since 2019, a fishing ban policy for the species in the Yangtze River has been introduced in China for resource restoration. Otoliths are calcium carbonate structures, and otolith microchemistry can provide detailed life history information that can be used to compare habitat use between different saline water bodies. To study the habitat history of C. nasus in the Anqing section of the Yangtze River after the implementation of the fishing ban, we examined the microchemical characteristics (Sr and Ca) of otoliths from the long (previously named C. ectenes) and short maxillary (previously named C. brachygnathus) types of anchovy using electron probe X-ray microanalysis (EPMA). Line-transect analysis of Sr/Ca ratios suggested that the short maxillary type of C. nasus could be divided into two groups. The otolith Sr/Ca ratios (calculated and expressed as Sr/Ca ×1,000) of one group were always < 3.0, indicating their freshwater residency. Those of the other group had phases of low (< 3.0, believed to be indicative of a freshwater habitat) and high values (> 3.0, believed to be indicative of a brackish or seawater habitat), indicating that anchovies not only have a freshwater habitat history with low salinity but also a brackish habitat history with high salinity. The latter group of anchovies were typically anadromous C. nasus, as the Sr/Ca ratio of the otoliths of C. nasus fluctuated significantly and coincided with variations between freshwater and estuarine brackish or seawater (i.e., anchovies experienced not only freshwater habitats but also brackish water habitats at different stages of their life history). The Sr content mapping of EPMA with different color patterns for freshwater (blue), brackish water (green-yellow) and seawater (red) habitats also confirmed the results obtained from the line-transect analysis. Our results demonstrated that the population composition of C. nasus in the Anqing section of the Yangtze river became complex, and there was coexistence of freshwater resident and anadromous C. nasus in the Anqing section of the Yangtze River in Anhui Province, China (i.e., freshwater resident and anadromous short maxillary and anadromous long maxillary type C. nasus). This phenomenon may suggest a restoration of C. nasus resource diversity after the implementation of the fishing ban in the Anqing section of the Yangtze River.