长江南京江段长颌鲚生境履历的反演研究

利用电子探针显微分析技术(EPMA),对2009年和2014年采自长江南京段的长颌鲚耳石微化学进行了研究,反演了其生境履历.结果显示,这些长颌鲚耳石上元素Sr/Ca值的动态可分为两类.一类Sr/Ca值出现显著波动,不仅具有对应淡水生境的低值(1.87±0.36),而且有对应于河口半咸水生境的较高值(4.80±0.80),甚至出现了外海高盐度生境的高值(7.85±0.57),反映了溯河洄游的生境履历特征.另一类Sr/Ca值稳定3.0以下(14NJC09和14NJCE10),仅反映出在淡水生境中生活的履历.上述结果均得到了耳石Sr面分布的验证.上述“反演”的结果首次发现,传统上认为的一定是溯河洄游的长颌鲚,也可能存在有淡水定居个体.单纯利用上颌骨的长短并不能作为有效判别长江刀鲚资源群体中溯河洄游个体和淡水定居个体的标准.

Inversion of habitat history for the long-jaw ecotype Coilia nasus collected from Nanjing section of the Yangtze River

To understand the migration characteristics of long-jaw grenadier anchovy Coilia nasus, an electronic probe microanalyzer (EPMA) was applied to analyze the micro-chemistry patterns of element Sr and Ca in otoliths of ten C. nasus (length ratio of upper jaw/head>1) collected from Nanjing section of the Yangtze River in 2009 and 2014. The results of line transect analyses showed that the Sr:Ca ratio (i.e., Sr/Ca×103) in the otolith of the anchovies could be divided into two types: (1) Sr/Ca ratio had a fluctuation pattern between low (<3.0) and high (>3.0) phases in the otolith, suggesting the individuals were anadromous eco-type which experienced not only the freshwater, but also the brackish water even the sea water at different stages in their life history. (2) Sr/Ca ratio was consistently at low phase (<3.0) throughout the otolith, indicating that the individuals only experienced freshwater habitat during its whole life history. These evidences were supported by the Sr mapping analyses. The results found, for the first time, that long-jaw grenadier anchovy could be the individual of freshwater resident eco-type, although it is traditionally believed that all of them in the Yangtze River are diadromous eco-type. The former with low commercial value and the latter with high commercial value cannot be effectively distinguished from each other only by the upper jaw length of C. nasus.