L. BRUNET AND M. J. SABO, School of Forestry, Wildlife and Fisheries, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA

Large areas of sunfish spawning habitat become hypoxic (dissolved oxygen concentrations < 2.0 mg/l) during the late spring and early summer months in the Atchafalaya Basin. In order to effectively guard nesting territories, male sunfish must exhibit aggressive behavior towards perceived intruders. In aquaria, we performed tests with intruder models and food items to determine if the behavior of males of two sunfish species (bluegill Lepomis macrochirus and spotted sunfish L. punctatus) differed when inhabiting low and high dissolved oxygen concentrations. Behavioral reaction time to a food item (worm) under hypoxic conditions increased in both bluegill and spotted sunfish. When presented with fish-model intruders, bluegill became more passive, less alert, and less aggressive under hypoxic conditions; while spotted sunfish became slightly less passive, more alert, and less aggressive. Hypoxia causes male bluegill to respond more passively when challenged, but spotted sunfish remain alert when inhabiting hypoxic habitats.