群体大小对麦穗鱼幼鱼凝聚力和协调性的影响

The Effect of Group Size on Shoal Cohesion and Coordination in Juvenile Pseudorasbora parva

为探讨群体大小对麦穗鱼(Pseudorasbora parva)幼鱼集群特征的影响,在(25±1)℃水温下对分别由1,2,4,8,16尾实验鱼组成的5个群体(每群体8个重复)进行视频拍摄及轨迹分析,计算和分析了游泳速度及群体中不同个体空间分布的相关数据,据此得到群体的凝聚力和协调性。结果显示:麦穗鱼的最近邻距离介于3~6cm(1~2倍体长)之间,且2个体组显著大于4,8,16个体组(p<0.05);群体排列的极性随群体增大而显著下降(p<0.05);麦穗鱼自发游泳速度多为0~10cm·s^(-1),且随着群体的增大有下降的趋势;群体中不同个体间游泳速度的同步性随着群体的增大而显著下降(p<0.05)。结果提示:麦穗鱼的最近邻距离随群体增大而下降,即凝聚力增加,从而显示出该鱼具有典型的集群行为;随着群体增大,群体游泳速度同步性和极性的下降则说明该鱼协调性随群体增大而下降。

To explore the effect of group sizes on motion feature, eight repetitions of Pseudorasbora parva juveniles with different group sizes （1, 2, 4, 8 and 16 individuals per group） were videoed at water temperature of （25±1） ℃ for 15min （15 frames · s^-1）, from which the coordinates of each individual were acquired and the swimming speed of individual spontaneous movements and the shoaling distribution structure of fish groups with different sizes were analyzed. The results showed that： 1） the median nearest neighbor distance （NND） mostly exhibited between 3 to 6 cm （1~2 BL）, the NND of 2 individuals significantly larger than the oth- er groups （4, 8 and 16 individuals groups） ; 2） the juvenile Pseudorasbora parva showed high levels of polarity of orientation within a group （80% to 94% individuals moving with the same direction）, which significantly decreased with group sizes; 3） juvenile Pseudorasbora parva swam mostly at a speed between 0 to 10 cm · s^-1 （81%~90%）, with the median swimming speed showed no significant difference among different group sizes; 4） the synchronization of swimming speed among fish individuals within each group decreased with increased group sizes. The results suggested that： 1） juvenile Pseudorasbora parva showed typical shoaling behavior as shoal cohesion increased with group size indicated by NND; 2） the shoal coordination decreased to some extend with group size increased from 1 to 16 individuals as indicated by decreased synchronization of swimming speed and decreased orientation polarity in large size group.