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Locomotion is vital to the survival and fitness of animals and dominates daily energy budgets. The main energy consuming process of locomotion is the muscle activity needed to maintain stability or generate propulsive forces. In fish, the speed of swimming is thought to depend on the gait type, which may reflect an energetically efficient locomotory behavior. Bluegill Sunfish (Lepomis macrochirus) exhibit either steady or intermittent (burst-coast) gaits when swimming in the field, but whether these gaits differ in their energetic efficiency is unknown. We analyzed the electromyography (EMG) of oxidative muscle in Bluegill swimming at low velocities to determine if steady swimming is more or less energetically efficient than intermittent swimming. EMG data were acquired using bipolar fine wire electrodes implanted into oxidative musculature at 2/3 tail length. Steady swimming EMGs were recorded in a flume (fish treadmill) at incrementally increasing speeds relative to body length, until nonoxidative muscle was recruited. As speed increased, EMG intensity increased, which corresponds to increased muscle recruitment. Fish reached maximum EMG intensity (100% oxidative muscle capacity) between 1.75 - 2.25 BL/s. Intermittent swimming EMGs were recorded while the fish swam volitionally in a pool. The burst phase consisted of 2-3 tailbeats, followed by a coast phase duration of 1 second or less. Based on preliminary results, fish in the pool swam at an average of 62.1% (n = 10) of their maximum oxidative capacity. When intermittently swimming, muscle activity was 37.9% more efficient than steady swimming at similar speeds. This demonstrates that when swimming volitionally Bluegill choose the most energetically effective gait. However, further analysis is needed to determine how individual variation affects swimming performance. Continued comparison of these methods of locomotion will broaden the understanding of energy decisions that fish make. These results suggest that intermittent swimming is the more energetically efficient form of aquatic locomotion. This work is supported by NSF grant award number 2135851. 

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.