渤海当年生小黄鱼矢耳石微结构特征

Sagitta Microstructure Characteristics of Young of the Year(YOY)Larimichthy polyactis in the Bohai Sea

以渤海海域采集的小黄鱼(Larimichthy polyactis)幼鱼为研究对象,分析其矢耳石的微结构特征。结果显示,小黄鱼矢耳石中心核呈圆形,平均直径为(24.35±0.72)μm,核内耳石原基为深黑色的圆形结构,平均直径为(12.07±0.58)μm,第1日轮距中心核的距离为(14.11±1.08)μm。初次摄食标记轮出现在第4条日轮处,标记轮暗带颜色加深、清晰可辨,该标记轮距中心核的距离为(20.67±2.28)μm。小黄鱼矢耳石前20条日轮,轮纹由圆环状逐渐变为椭圆,沿最长轴方向的轮纹宽度变化范围为6.51~14.37μm,且随着日龄的增加而逐渐变宽;20~40条日轮间轮纹宽度呈显著升高,40~85日龄轮纹宽度变化相对平稳,第56~60条轮纹处出现轮纹,平均宽度最大值为41.59μm。在小黄鱼矢耳石日轮沉积过程中,伴随着亚日轮结构的形成,亚日轮清晰度差,轮纹宽度较窄且波动较大,在显微镜下对视野轻微调焦时会暂时性“消失”。本研究对小黄鱼的矢耳石特征结构进行了分析,以期为野生小黄鱼及其他鱼种的日轮判断提供参考。

Sagitta microstructure of young of the year Larimichthy polyactis collected in the Bohai Sea was studied,which is routinely used for age analyses.Results showed that there was usually one circular nucleus with one deeply black primordium in it,and only a few samples presented two nuclei or primordia.Average diameter of sagitta nucleus and primordia were(24.35±0.72)μm and(12.07±0.58)μm,respectively.The first increment was observed on the second day,with a distance of(14.11±1.08)μm to the central nucleus.The first feeding check appeared on the 4th increment,with a distance of(20.67±2.28)μm to the central nucleus,displaying larger width,deeper color,and higher clarity.From the otolith nucleus to approximately the 20th increment,increments gradually changed from a ring shape to an ellipse.Increment widths in the long axis ranged from 6.51μm to 14.37μm and tended to increase with age.Increment widths dramatically rose until approximately the 40th increment,reaching a value of(36.05±8.32)μm.Thereafter,increment mean width did not show any clear trend.The process of daily increment deposition of L.polyactis was accompanied by the formation of sub-daily increments.Sub-daily increment deposits displayed a lack of periodicity,irregularity,low clarity,and incompleteness compared with daily increments.Changing the depth of the field while observing these less defined increments resulted in a temporary elimination of the sub-daily increments from view.The analysis of otolith increment deposition has been widely applied and developed in age validation of larvae and juvenile fishes.The counting results directly determine analytical accuracy of the hatching date,spawning field distribution,and migration of wild individuals.The numerous presence of sub-daily increments will increase the difficulty of discriminating daily increments.L.polyactis has well-developed sagitta,which possesses greater width of daily increment and a greater number sub-daily increments.Therefore,distinguishing daily increments from sub-daily increments is the primary task of the research on the sagitta microstructure of L.polyactis.In the present study,the sagitta microstructure characteristics of L.polyactis were analyzed to provide a reference for daily increment judgment of wild L.polyactis and other fish species.Meanwhile,this study will supplement the biological information on L.polyactis and provide data for resource surveys of wild populations.