| Abstrakt: |
AbstractWhile electrofishing has become a common capture technique in fisheries research, the potential impact of this technique on the fish is not completely understood. Mature female chinook salmon Oncorhynchus tshawytschaand eggs at key developmental stages were electroshocked with 10-s pulsed DC from a standard backpack electroshocker in a controlled environment. Eggs from one-third of the shocked females showed extreme mortality (>93%), while the remaining shocked families shared egg mortality (12-20%) similar to the controls (9.9%). Eggs shocked at the early eyed stage showed significantly higher mortality (34.2%) than control (unshocked) eggs, while mortalities were low (≤2.1%) for shocked eggs and for controls at all other developmental stages. Upon examination of fish radiographs, we found that the electroshocked juvenile fish had significantly more spinal aberrations than the unshocked fish. Hematocrit, serum cortisol and glucose, serum lysozyme activity, and total leukocyte counts were monitored in control and shocked juvenile fish for 3 weeks. Hematocrit declined over 3 weeks in both groups. Serum cortisol and glucose levels increased significantly in both groups within 12 h, but shocked fish showed a slower return of cortisol levels to preshock values and an overall higher glucose response. The combination of electroshock and handling did not affect serum lysozyme levels, but unshocked (handled) fish exhibited immediate and significantly reduced lysozyme activity for up to 2 weeks. Total leukocyte numbers were higher in shocked fish late in the experiment (at 2 and 3 weeks). Although electrofishing is useful to determine the precapture physiological status of field-caught fish, our data show that electrofishing can have significant detrimental impacts on the fish. |
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