Effects of polychlorinated biphenyls on the schooling behavior of Japanese medaka (Oryzias latipes).

The effects of polychlorinated biphenyls (PCBs; Kanechlor 400) on the schooling behavior of Japanese medaka (Oryzias latipes) were tested after feeding with various concentrations of PCBs (0, 1, 5, 25, and 125 microg/g). To test schooling, three PCB-exposed medaka and three untreated fish were placed in one chamber, and their swimming trajectories were recorded. Swimming velocity, turning angle, and nearest-neighbor distance (NND) were analyzed individually, and the polarization and expanse of each schooling group were analyzed. Fractal dimension analysis was performed for trajectory, swimming velocity, and turning angle. Six behaviors (school formed by six swimming medaka, school formed by six stationary medaka, school formed by three to five swimming medaka, school formed by three to five stationary medaka, swimming without schooling, and stationary without schooling) were quantified with time. Behavioral parameters were the same for PCB-exposed and unexposed medaka in the same schooling group. Swimming velocity decreased in a dose-dependent manner, and NND in the group exposed to 25 microg/g of PCBs was significantly longer (126%) than that in the controls. The fractal dimensions of trajectory and turning angle increased significantly in the highest PCB-exposure group, indicating that schools containing PCB-exposed individuals frequently changed direction. The PCBs shortened the time of school formed by six swimming fish, which was 23.7% of the control value in the group exposed to 25 microg/g of PCBs. The frequency of collisions between individuals was significantly greater in the highest-exposure group (31.3) than in the controls (13.3). Thus, PCB exposure influences the behavior of unexposed fish in the same school, consequently affecting schooling behavior.