ASSOCIATION BEHAVIOR OF YOUNG STRIPED JAC K PSEUDOCARANX DENTEX TO A SHADE OF FLOTSAM

Behaviors of the striped jack Pseudocaranx dentex to the shade of flot sam were observed in experimental tanks to determine whether or not th e shade would act as a factor to trigger association behavior of fishe s to a flotsam. During the daytime, 20 fish of 23 cm TL preferred to d istribute under the cover which was set on the right half side of a 90 m(3) outdoor tank, while there was no difference in fish distribution between the right and left sides in a control tank without cover. Dur ing the nighttime, however, there was no difference in horizontal dist ribution between the test and the control tanks. Fish in the test tank tended to distribute at shallower depths than those in the control ta nk during the daytime, while both fish distributed at the surface duri ng almost all of the nighttime. When the light intensity was increased by more than 10,000 1x in an outdoor 60 m(3) tank with a 90 x 180 cm plywood board at the surface, 21 striped jack of 24 cm TL distributed in the shade of the plywood board, while they went out of the shade an d swam around the tank when the decrease in light intensity exceeded 1 0,000 Lx. These data suggested that the shade might attract the stripe d jack and trigger the association behavior. It was also suggested tha t in marine ranching of the striped jack in coastal waters the feeding station should provide fish with shade to enhance their association b ehavior and to keep fish at a fixed area in the sea.