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P1-97: In early summer, nesting Bluegill Sunfish (Lepomis macrochirus) expend large amounts of energy building nests, spawning, protecting their offspring, and chasing away predators. The energetic demands of nesting are likely significant and may heavily influence their life history and reproductive success. However, the exact metabolic cost of nesting is difficult to quantify without precise information about the three dimensional position of the center of mass of nesting fish. Field observations of Bluegill Sunfish nesting in Lake Waban (Wellesley, MA) were obtained throughout June until early July by using underwater cameras, fitted with a temperature and light sensor, calibrated to allow three dimensional tracking. The positional data of nesting Bluegill Sunfish were analyzed to derive velocity and acceleration in order to calculate their metabolic rate. We chose to analyze repetitive nesting behaviors, such as rim circling and defensive chasing, due to their frequency of occurrence and consequentially high metabolic demand. Using metabolic rates calculated from Bluegill swimming in a flume, we found that rim circling is nearly 22.2 times more metabolically expensive than the average metabolic cost of swimming in a straight path for the same velocity and duration. Since rim circling is so metabolically expensive and since we estimate that rim circling occurs nearly 25,500 times during an 8 day nesting period, our results strongly suggest that the nesting cycle is one of the most critical periods in the life history of Bluegill Sunfish. The high energetic demands of nesting and the temporary bout of starvation while the fish occupies its nest results in a small margin of error for reproductive success. These conclusions deepen our understanding of male Bluegills’ true paternal investment and can serve to illuminate our understanding of their life history from a quantifiable perspective.