Behavioral Responses To Predation Stress In Four Cyprinid Fish Species

In nature,fish are often subjected to different degrees of predation stress.Thus,the fish have developed a variety of anti-predator strategies.Among them,the anti-predator behavior is relatively efficient and highly plastic,thus it attracts much attention.To examine(1)the effects of predation experience,starvation and schooling on the anti-predator behavior of fish,(2)the inter-species differences of the anti-predator behavior among cyprinids.This study has carried out the following two aspects of research content:(1)The effects of predation experience and starvation on behavioral characteristics in juvenile qingbo(Spinibarbus sinensis)[the experiment was carried out in the case of single fish and group(5 fish)respectively];(2)The interspecies comparison on behavioral response to predation stress among breams(Parabramis pekinensis),grass carp(Ctenopharyngodon idellus),crucian carp(Carassius auratus)and qingbo.The experimental results are as follows:1.Fish from all groups showed increased activity when tested collectively compared to individually(P<0.001).The predator-experienced fish showed decreased locomotor activity to predators as an antipredator strategy when tested as singletons;however,increased locomotor activity occurred when tested in a group.2.Starvation elicited increased activity indicating increased foraging willingness when tested in a group(P=0.001);however,the difference between starved and normal-fed fish was no longer significant when they were tested as singletons.Compared with the control fish,the double-treated fish showed no difference in activity when tested both individually and collectively.3.When predators were present in the testing environment,juvenile breams with predation experience were more exploratory than that of the controls(P<0.05);In the absence of predators,predation experience led to a decrease in the exploratory ability of juvenile grass carps,while in the presence of predators,predation experience led to a significant increase in the exploration,activity and boldness of juvenile grass carps(P<0.05).4.Regardless of the presence or absence of predators in the testing environment,predation experience led to a significant increase in exploration and activity of juvenile crucian carp(P<0.05).The presence of predators in the testing environment led to an increase in the activity of juvenile qingbo(P<0.05).The above results suggested that:1.Schooling significantly affects the anti-predator and foraging behavior of fish,which may be related to the decrease of predation risk and the intensification of food resource competition caused by schooling.2.The effects of predation and starvation on the behavior of qingbo may offset each other.In addition,the strong stress response and the deterioration of physical condition caused by multiple stresses also had an impact on the anti-predation behavior of the experimental fish.3.The effects of predation experience and testing environment on behavioral characteristics of breams,grass carps,crucian carp and qingbo were significantly different between species.Grass carps are more sensitive to predation experience and testing environment,while qingbo is more conservative.But in general,when predators are present in the current environment,all four cyprinids respond to predators by maintaining highly locomotive state.4.The early experience of predation stress has a distinct effect on fish from the predation stress present in the current environment.Compared with the former,the presence of predators in the current environment is more urgent and direct stress for fish.However,early predation experience can help the prey fish to quickly and accurately identify the predator,and then make the appropriate anti-predator response in time,so it is crucial for the survival of fish.