| Food resources and predation pressure are two important factors affecting the behavior of fish, which frequently cause a situation of selection dilemma between survival and growth in fish species. On the one hand, fish individuals might be more likely to meet the predator and more vulnerable to attacks if they prefer to leave the hidden place more frequently for foraging activities, whereas on the other hand, the reduced foraging activities might weight against their growth performance if they prefer to spend more time in shelter. In order to explore the behavioral strategies of fish species to variation of food resources and predation pressure, and whether such strategies be affected by the life history, qingbo juveniles were selected as experiment object in this study and three series of experiments were conducted accordingly. In experiment I, we paired the fish individuals which were either predation experienced or predator-na?ve and hence formed the control group, mixed group, predation group. We measurement the behavior of three groups of experimental fish under two condition(one without predator presence while the other with predator presence in measuring device), respectively. In experiment II, we paired the fish individuals which were either2 weeks of starved or normal fed and hence formed the control group, mixed group,starvation group. We measurement the behavior of three groups of experimental fish under two condition(one without food presence while the other with food presence in measuring device), respectively. In experiment III, we paired the fish individuals which were either both predation-experienced and starved or predation-na?ve and normal fed and hence formed the control group, mixed group, starvation+predation stress group.We measured the behavior of three groups of experimental fish under four conditions(i.e. with no presence of predator or food, presence of only predator, presence of only food and presence of both predator and food in measuring device), respectively.The main findings of this study are as follows:(1)Both prior predation experience and predator in measuring environment showed significant effects on the time of first access to exploring area, total durations in exploring area, times of entries to exploring area and the swimming speed and distance between qingbo pair in exploring area(P≤0.05). Compared with the fish of control group,whether predators presented or not, the time of first access to exploring area, and distance between the paired fish and the swimming speed of predation experienced group were reduced. The presence of predators resulted in shorted time of first access toexploring area, increased entries times and decreased swimming speed of control group and predation experienced group, whereas the presence of predator also resulted in the increased total durations in exploring area and decreased distance between paired fish individuals in control group. Compared with the predation experienced group, the time of first access to exploring area of mixed group were postponed, but there were no significant difference between the two groups on other indicators, under the condition of no presence of predator in measuring environment.(2)Both starvation experience and presence of food in measuring environment showed significant effects on the time of first access to exploring area, durations in exploring area, entries times to exploring area, swimming speed and its correlation coefficient between paired fish individuals and the distance of paired qingbo when lingered in exploring area(P≤0.05). Compared with the fish of control group, whether food presented or not, the time of first access to exploring area was shorten in starvation group. When no food was presented, the total duration, entries times and speed correlation coefficient of paired fish individuals when swam in exploring area increased in starvation group, whereas the swimming speed and distance of paired fish individuals in exploring area decreased in starvation group. However, when food was presented in measuring device, the total durations and the average time per visiting in exploring area decreased, the times of entries reduced, the swimming speed and distance between paired individuals increased in starvation group. Compared with the fish of starvation group, the times of individual fish entered to exploring area alone increased in the mixed group, whereas there were no significant difference between the two group on other indicators, under the condition of food presence in the measuring device.(3)The experience of both starvation and predation showed significant effects on the time of first access to exploring area, durations and the average per visiting in exploring area, times of entries to exploring area, swimming speed, speed correlation coefficient and distance between paired fish when swam in exploring area(P≤0.05).Compared with the fish of control group the average per visiting to exploring area of starvation + predation exprienced group decreased, while the distance between paired fish and the swimming speed increased under the condition of presence of predator in measuring device. The swimming speed of starvation + predation experienced group increased under the condition of presences of predator and food in measuring device.Compared with the starvation + predation experienced group, the times of entries to exploring area of mixed group reduced under the condition of predator presence in measuring device.There were no significant difference on the behavior indicators between the two fish individuals in mixed group in all the three experiments,in addition to frequency by alone.The studies shows that:(1)Predator shows profound effect on the behavior pattern of qingbo juvenile,while food shows little effect. With the presence of predator in the environment, the activity of qingbo juvenilein exploring area increased. The behavior pattern of qingbo juvenile with both predator and food presented in environment are more prone to thebehavior pattern when predator is presented in environment.(2)The experience of starvation, as well as the experience of predation can lead to alteration of the behavior pattern in qingbo juvenile, with the predation experience results in a more prudent behavioral strategy. However, the exploratory behavior enhanced by starvation possibly due to the increased requirement of energy.(3)For qingbo juvenile that experienced both starvation and predation, both experiences acted interactively on behavior pattern and show profound effects on its behavioral strategy.(4)The fish of mixed group show distinctly different behavioral pattern compared to either control or treatment group, whereas it is not the simply the offset of the effects between both groups. |
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