Foraging tactics and home range of dark chub in a Japanese river

The foraging tactics of dark chub, Zacco temmincki were classified into "sit-and-wait" where fish remained stationary in running water, "stop" where fish remained stationary in still water, and "cruising" where fish moved widely near the water surface. Sit-and-wait foragers primarily fed upon invertebrates that were carried by the current or fell onto the water surface, whereas cruising foragers fed upon algae and invertebrates that fell onto the water surface. Stopping individuals only fed occasionally. The percentage of sit-and-wait foraging increased as current velocity increased, whereas the percentage of cruising foraging was negatively affected by both current velocity and fish density. Larger individuals and males employed sit-and-wait foraging more frequently than smaller individuals and females. Hom range was large for cruising foragers. Aggressive interactions were frequent among sit-and-wait foragers. Although behavioural patterns of dark chub markedly differed between running and still waters, the gut content and growth rate did not differ significantly between the two habitats.