柳江下游大眼鳜仔稚鱼耳石特征及孵化期推算

Otolith characteristics and incubation period estimation of larval and juvenile Siniperca knerii in the lower reaches of Liujiang River

【目的】分析柳江下游大眼鳜(Siniperca knerii)仔稚鱼的耳石形态变化和微结构特征,明确该江段大眼鳜的生长和繁殖现状,为其资源保护及合理开发利用提供理论依据。【方法】以2022年采集的柳江下游大眼鳜仔稚鱼为试验材料,经50%乙醇麻醉后测量体长(mm),用解剖针挑取耳石;采用温度标记法确证矢耳石轮纹增量周期;通过显微镜观察矢耳石和微耳石形态特征并统计耳石轮纹数,利用耳石日轮技术推算其孵化日期;通过Image J测量矢耳石与微耳石的长(μm)、宽(μm)、周长(μm)和面积(μm^(2))等形态指标,并计算环率、矩形趋近率、椭圆度、辐形比、外形尺寸和圆度等形状指数,比较两类尺寸等级(体长≤13 mm和体长>13 mm)的大眼鳜矢耳石形态变化,对大眼鳜矢耳石形态指标与体长关系进行拟合,采用AIC(Akaike information criterion)准则选取最适模型,分析二者间的关系。【结果】2022年采集的大眼鳜样本微耳石轮纹数范围为3~9轮,矢耳石轮纹数范围为6~16轮,矢耳石标记轮纹数与标记时间呈线性相关,大眼鳜矢耳石轮纹增量具有日周期性,用日轮数N+3表示日龄,推算2022年柳江下游江段大眼鳜样本的孵化期为5月1日—8月8日。随着大眼鳜仔稚鱼的生长,矢耳石由近圆形发育成一端略尖的桃形,微耳石由近圆形发育成贻贝形,矢耳石相较于微耳石变化更明显。拟合大眼鳜矢耳石的长、宽、周长和面积4个形态指标与体长的关系,以线性模型为最佳拟合模型,两类尺寸等级的大眼鳜矢耳石形态指标与体长相关性均较强,第二类R2大于第一类,两类尺寸等级的线性模型拟合效果无显著差异,表明大眼鳜仔稚鱼在早期生活阶段耳石形态与体长呈线性相关,且在一段时间内相关性逐步增强。【结论】柳江下游大眼鳜仔稚鱼孵化期整体短于珠江流域鳜属鱼类的自然繁殖期,矢耳石更适合作为大眼鳜早期年龄鉴定的器官,耳石的大小可作为判断该物种早期生长现状的重要依据。

【Objective】The purpose of the study was to analyze the morphological changes and microstructural charac‐teristics of otolith in Siniperca knerii larval and juvenile fish in the lower reaches of the Liujiang River,and to explore the current growth and reproduction status of S.knerii in this section of the river,so as to provide theoretical basis for resource protection and rational development and utilization of S.knerii.【Method】The S.knerii larval and juvenile fish col‐lected from the lower reaches of Liujiang River in 2022 were used as experimental materials.After anesthesia with 50%ethanol,the body length(mm)was measured,and the otolith was selected with anatomical needle.Temperature marking method was used to confirm the increment period of sagitta otolith marking ring.The morphological characteristics of sa‐gitta otolith and lapillus otolith were observed by microscope and the number of otolith marking rings were counted.The incubation date was extrapolated using otolith daily increment technology.The morphological indices of length(μm),width(μm),circumference(μm)and area(μm^(2))of sagitta otolith and lapillus otolith were measured by Image J.And the shape indices such as circularity,rectangularity,ellipticity,aspect ratio,shape size and roundness were calculated.The morphological changes of sagitta otolith of S.knerii body length of two types of size classes(body length≤13 mm and body length>13 mm)were compared,the relationship between the morphological indices of S.knerii sagitta otoliths and body length was fitted,and the optimal model was selected using Akaike information criterion(AIC)to analyze the relationship between the two.【Result】S.knerii samples collected in 2022 ranged from 3 to 9 lapillus otolith marking rings and 6 to 16 sagitta otolith marking rings.The number of sagitta otolith marking rings was linearly correlated with the mar-king time.The increment of S.knerii sagitta otolith marking rings was daily periodic,and the day age was represented by the number of daily rings N+3.It was estimated that the incubation period of S.knerii samples in the lower reaches of Liu‐jiang River in 2022 was from May 1 to August 8.With the growth of S.knerii larval and juvenile fish,sagitta otoliths de‐veloped from near round to peach-shaped with a slightly pointed end,and lapillus otoliths developed from near round to mussel shaped.Changes of sagitta otoliths were more obvious compared to that of lapillus otoliths.The linear model was the best fitting model to fit the relationship between body length and four morphological indices:length,width,circum‐ference and area of the sagitta otoliths of S.knerii.The correlation between the morphological indices of otoliths and body length of S.knerii in two size classes was strong.The R2 of the second class was larger than that of the first class,and there was no significant difference in the linear model fit effects between the two size classes.The results indicated that the otolith morphology of S.knerii larval and juvenile fish was linearly correlated with body length in the early life stage,and the correlation gradually increased in a period of time.【Conclusion】The incubation period of S.knerii larval and juvenile fish in the lower reaches of the Liujiang River is overall shorter than the natural breeding period of Siniperca fishes in the Pearl River Basin.Sagitta otolith is a more suitable organ for early age identification of S.knerii,and the size of the oto‐lith can be used as an important basis for judging the early growth status of this species.