| Most of the animals in nature,such as fish,always are living together and moving in a way of high coordination.These animals can exhibit complex collective behavior which is a widespread phenomenon within animal kingdom for part or all of their lifehistory,and it is also an important survival strategy for fish.Compared with solitary individual fish,the group living can confer not only ecological benefits but also costs to individuals of animals.Although group living is conducive to obtain food,many factors such as complex and varied natural environment as well as intense intraspecies competition often lead to individual fish facing starvation stress.There are great individual differences in phenotypes(such as aerobic scope,AS)in fish,which can affect the ability of occupying spatial position within a group,and then have an influence on the ecological benefits and risky costs of individuals,and finally present in the population dynamic process.To investigate the effects of nutritional status and aerobic scope on schooling behavior in fish,the present study used juvenile goldfish(Carassius auratus)with similar body weight and healthy condition as experimental model at(25.4±0.2)~oC,which included 19 batches(total 760 individuals)with each batch having 40 individuals.Firstly,the feeding metabolism(usually termed special dynamic action,SDA)was measured in 40 fish with depriving of food for a week and 40 fish with normal nutritional status to determine the multiple regression equations between metabolic rate and feeding level,SDA duration,and fish body mass.Secondly,fish of each batch was measured their standard metabolic rate(SMR)and maximum metabolic rate(MMR)for calculating aerobic scope(AS=MMR-SMR).According to the combinations of AS and nutritional status,six fish of each group were conducted a color-tagging under the scales,and finally the schooling behavior of each group was recorded via a wide-angle camera.In the present study,five treatments were set,including the control treatment(3high AS and 3 low AS individuals at normal nutritional status of fasting for 24 h),the starvation treatment(3 high AS and 3 low AS individuals at a fasting status of 1 w),the mix treatment 1(3 high AS individuals fasted for 1 w and 3 low AS individuals at in normal nutritional status of fasting for 24 h),the mix treatment 2(3 low AS individuals fasted for 1 w and 3 high AS individuals at in normal nutritional status of fasting for 24h),and the mix treatment 3(3 individuals fasted for 1 w and 3 individuals at in normal nutritional status of fasting for 24 h,both phenotype having similar AS).Individual spatial position within schooling,individual food intake,individual characteristic parameters(including individual swimming speed,acceleration and total swimming distance)and group characteristic parameters(including group swimming speed,group acceleration,the total swimming distance,synchronization of individual swimming speed,individual distance,nearest neighbor distance and polarity)were measured from the videos.The results of the present study are describing as follows:(1)No significant effect of nutritional status and aerobic scope on individual spatial position within schooling was found,and the total food intake of the starvation treatment was less than those of the control treatment and the three mixed treatments.(2)In the control treatment,there were negative correlations between food ration,meal size during the feeding and individual spatial position during feeding,postprandial30 min and postprandial 150 min of C.auratus.In other treatments,the individual spatial position did not correlated with the food intake and meal size at the all feeding and digestive stages.(3)In addition to the starvation treatment,the residual AS was negatively correlated with the food intake and meal size of the control treatment and the three mixed treatments.(4)During the acclimation period,there was no significant difference in individual swimming speed between the starvation and the control treatment,but the individual swimming speed was slower in the three mixed treatments than both the control and starvation treatment,and no difference in individual swimming speed was found among the three mixed treatments.The individual swimming speed of all five treatments was the highest during the acclimation period,the lowest during the feeding period,and the intermediate during the digestion period.The total swimming distance was similar to the individual swimming speed.There is no effect of starvation on individual swimming acceleration during the acclimation period,and the individual swimming acceleration was significantly higher at the acclimation stage than those of the other stages.During both the adaptation and feeding period,there was no significant difference in individual swimming acceleration among all treatments,but there were differences in this parameter among the three digestive periods.(5)The movement speed of the group was similar to the individual swimming speed,and starvation did not affect the movement speed of the group during the acclimation.The group swimming speed was decreased in the control,starvation and mixed treatment 1 during the feeding period,and the group swimming speed during the feeding period was lower than other periods in the mixed treatment 2 and 3.During the process of food digestion,the group swimming speed of the control,starvation and the three mixed treatments all decreased.The result of group movement distance was consistent with the group swimming speed.The results show that starvation did not affect the acceleration of the group swimming during the acclimation period,and the group swimming acceleration during the acclimation period of all treatments was lower than those of both the feeding and digestion periods.(6)There was no difference in IID and NND among the acclimation,ingestion,and digestion periods in all treatments,and no difference in IID and NND was found among all treatments during any of five periods.No significant difference in synchronization of individual swimming speed was found between the starvation and control treatment during the acclimation period.Similarly,synchronization of individual swimming speed did not show difference between the control and starvation treatment during the feeding and digestive periods.During the acclimation period,the group polarization of the starvation treatment was not different from the control treatment.During the feeding and digestion stages,the group polarization of the starvation treatment was lower than that of the control treatment.The group polarization of all treatments was lower at feeding stage than those at both the acclimation and digestion periods.(7)In all treatments,the individual spatial position was obviously repeatable during all of the acclimation,ingestion,and digestion periods.Except of individual acceleration in the mixed treatment 1and group swimming acceleration in the control treatment,all of the nutritional status treatments had high repeatability in schooling behavior parameters.The suggesting of results in the present study is listing as follows:(1)Both the nutritional status and aerobic scope had no effect on the individual spatial position within schooling in gold fish(C.auratus).(2)Within the school of gold fish(C.auratus)of normal nutritional status,occupying the spatial position at the front of the school can confer to the ecological benefits of more food resources,but starvation eliminates the heterogeneity of ecological benefits of individual spatial position distribution within the school.(3)Starvation and digestion have no effect on the group cohesion of the gold fish(C.auratus),but the phenomenon that starvation reduces the group coordination only emerged during the digestion stage,and that is the individual difference in obtaining food in the group leads to different digestive strategies,which leads to more disordered swimming synchronization of individuals,and finally leads to the decline of group coordination.(4)The schooling behavior of gold fish(C.auratus)exhibited obvious variation within the group,but it still maintains stable phenotypic repeatability among different feeding and digestion stages,which indicates that this fish species has group personality. |
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