Previous experience alters individual vulnerability to angling of crucian carp (Carassius auratus)

In recreational fisheries, fish often undergo catch-and-release angling, which can lead to an indirect selection response of the behavioral traits of the fish. As individuals experience high-intensity angling activities, individuals learn to avoid being selected for artificial bait again, resulting in a change in the vulnerability to angling of fish, which is partly dependent on the cognitive learning ability of the fish. Here, we examined the relationship between vulnerability to angling and learning in juvenile crucian carp (Carassius auratus) under laboratory conditions. Our study had six angling treatments with each containing different group mates (i.e., the angling stress group, all fish that only experienced repeated angling stress practice for a period of three days; the learning group, all fish that only observed individual in the angling stress group to be angled; the control group, all fish that did not undergo any angling or learning; the mixed Group 1, fish are from the control and learning groups; the mixed Group 2, fish are from the control and angling stress groups; the mixed Group 3, fish are from the learning and angling stress groups), each of which consisted of five replicates). All fish were tested for boldness before and after the previous experiences (i.e., angling stress or learning) test. Our results showed that for the stress group, the total angling time, mean individual angling time and total number of bait touches all increased from Day 1 to Day 3, and the total angling rate decreased during the three days of the angling stress practice. After encountering the previous experiences, fish in the control, stress and learning groups all had increased boldness, as assessed by a shortened percent latency to emerge from the refuge. The change in the percent latency of boldness was higher in the stress group than in the learning group, with the control group being intermediate. Furthermore, no differences in the total angling time and total number of bait touches were detected among the six angling treatments, but the stress group exhibited the longest mean individual angling time and lowest angling rate compared with the other five angling treatments, indicating that angling-stressed individuals greatly decreased their vulnerability to angling after the previous angling stress. Our results show that changes in the vulnerability of crucian carp to angling were related to previous individual angling experience but not to visual social learning.