中文摘要：

为研究群体成员大小差异对不同喜好生境鱼类集群行为特征的影响,实验分别以鳊（Parabramis pekinensis）和中华倒刺鲃（Spinibarbus sinensis）幼鱼为实验对象,比较分析4尾等大小（E）和不等大小（2大2小,NE）实验鱼群体的自发游泳速度、空间分布以及对恐吓刺激反应等集群行为参数的差异.结果显示：（1）和鳊相比,中华倒刺鲃有更高的自发游泳速度、速度同步性和排列方向的极性,但二者对恐吓刺激的反应率及反应的协调一致性相似;（2）当群体成员大小出现差异时,两种鱼群体排列方向的极性不受影响,且大小个体成员间的速度及其同步性均没有差异,但整体的速度同步性与等大小群体相比有所下降;（3）个体间距离数据显示,个体大小差异不会影响两种鱼群体的凝聚力;（4）群体成员在两种鱼群中偏好位置不同,当群体成员大小不同时,大个体成员更偏好占据领头鱼位置;（5）群体成员大小的差异导致两种鱼对刺激的反应率下降.研究表明：中华倒刺鲃具有更高的活跃性、更好的群体运动的协调性,可能与其流水生境相关;当群体成员大小出现差异时,成员不分大小在整体上协调运动的速度和方向,并保持群体有较高的凝聚力,但两种鱼类自发游泳速度调整策略截然不同（鳊大小个体速度妥协趋同,而中华倒刺鲃低速个体速度提高）;群体成员大小差异导致鱼群对恐吓刺激的反应率有所下降,可能原因包括体形差异导致的社会因素造成敏锐性下降、信息交流效率受阻和（或）集群收益代价出现分化影响一致决策的形成等.

英文摘要：

The phenotypic composition of groups affect ecological and social processes, which is crucial for collectivebehavior research. To explore the influence of body size variation on shoal behavior between two cyprinids with different habitats, the juvenile Chinese bream （Parabramis pekinensis） preferring still water and Qingbo （Spinibarbus sinensis） enjoying flowing water were selected to study spontaneous swimming behavior, spatial structure and the responseto startling stimulus of fish groups including four similar fish individuals or including two larger and two smaller fishindividuals. The results showed that the spontaneous swimming speed, the synchronization of speed and the alignmentpolarity of the juvenile Qingbo were significantly higher than those of Chinese bream, and that the responses to frighten stimulus were similar between two species. The polarities of equalsize groups were similar to those of non-equalgroups while the non-equal groups showed lower synchronization of speed in both species. However, all measured variables were not different between large and small size individuals within non-equal size group. The difference in bodysize did not impact group cohesion. The larger individuals of heterogeneity in spatial structure preferred to stay at thefront of fish shoal. The flow regime habitats of Qingbo may explain its higher activeness and synchronization of swimming speed and alignment polarity than Chinese bream. Group members with different body size can coordinate theirswimming speed and direction of movements even with higher group cohesion. Interestingly, smaller Qingbo individuals elevated their speed to keep pace with larger individuals whereas Chinese bream individuals adjusted their speedto a moderate value. Variation of body size decreased the response ratio to frighten stimulus, possibly due to decreasedresponse acuity to external stimulus as a consequences of social factor （e.g. social hierarchy）, and impaired efficiencyof information flow and （or） the divergence of ecol