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<br />EXECUTIVE SUMMARY <br /> <br />The objective of this study was to assess the occurrence and rate of <br />electrofishing-caused injuries in endangered Colorado pikeminnow Ptychocheilus lucius <br />caught by boat mounted, pulsed-DC electrofishing systems. Colorado pikeminnow <br />captured by electrofishing during the Interagency Standardized Monitoring Program <br />were examined for external injury and x-rayed in the field to assess vertebral injuries. <br />Radiographs revealed that 12 of 46 Colorado pikeminnow x-rayed had vertebral <br />compressions. Three fish (7%) had vertebral compressions considered acute injuries <br />related to the electrofishing capture and nine fish (20%) had chronic (previous) or <br />congenital abnormalities. Vertebral compressions affected 2-11 vertebrae but most <br />fish (67%) had vertebral compressions of only two vertebrae. No fractured or <br />misaligned vertebrae were observed. Injury type was determined by vertebra <br />architecture (size, shape, and density) in each radiograph and was not validated with <br />necropsy because all fish were released alive due to their endangered status. Three of <br />47 fish examined had external injuries that included bruises and associated muscle <br />compaction, bleeding of the gills, and respiratory arrest. Respiratory arrest occurred <br />due to extreme tetany after one fish was trapped under a live anode for 15-30 seconds <br />resulting in prolonged exposure to tetanizing currents that stopped opercular <br />movement. Another fish was bleeding from the gills after capture while in electrotaxis <br />toward a cathode. Neither of these fish had observable vertebral damage. Information <br />about the capture of the fish with bruises and muscle compaction was insufficient to <br />relate the injury to observed electrofishing parameters but it was also the fish with <br />III <br />