EXPERIMENTAL CONSIDERATION ON GATHERING EFFECT OF FLOORSPLACED TO FLOATING FISH REEFS FOR TARGETED TRIDENTIGER OBSCURUS IN HYPOXIA ENVIRONMENT

We conducted laboratory experiment on the floating fish-reef structure in order to create a refuge habitat for Tridentiger obscurus, a fish species inhabiting the eutrophic Amagasaki Canal year-round and this trends were verified on field experiment. We aimed to clarify the effects of fish-reef with interstices and floor structures that imitated the water bottom on the behavior of the Tridentiger obscurus. We made the fish reefs by attaching floor structure underneath the PVC pipes providing interstices. The tank experiment results showed that the preference of Tridentiger obscurus to the PVC pipes increased when the floor was attached, and the number of individuals swimming in the water de-creased. This trend was enhanced by extending the length of the floor. In the field experiment in the Amagasaki Canal, the fish reefs with floors and PVC pipes had the highest population of fish. The results insist that when creating habitat for Tridentiger obscurus with fish reefs, it is effective to install surface structure 6cm for the fish to stay on, in the lower front side of the interstice entrances.