Preference based modeling of rheotaxis of Ayu (Plecoglossus altivelis altivelis)

Modeling fish behavior to observe if virtual fish can swim up a modeled river is a promising technique for estimating the easiness of fish migration. However, in many fish migration modeling researches, rheotaxis (the movement of fish in response to current) has been treated as an a priori driving force. Since rheotaxis is one of the most important factors that determine swimming direction, it should be expressed from the viewpoint of preference. In this research, we attempt to determine preference of rheotaxis based on laboratory experiments using adult and Juvenile Ayu (Plecoglossus altivelis altivelis). We conduct pair comparison of Ayu distribution between upper and lower section of a test watercourse using several velocity conditions (10, 30, 40 cm/s for Juvenile and 20, 30, 50, 70, 90 cm/s for adult). With velocities of 30 cm/s and 40 cm/s for juveniles, and 50 cm/s for adults, ayu distribution in the upper section showed a high level. Even when highly preferred illumination condition of 4000lx is set at the lower section, Ayu kept high distribution at the upper section. We define a procedure to calculate preference of rheotaxis and build it into our fish behavior simulation model on ArcGIS. The model could successfully reproduce observed fish migration behavior in a river.