Metabolic Responses of Juvenile Striped Bass to Exercise and Handling Stress with Various Recovery Environments

Abstract

Striped bass Morone saxatilis were exposed to exercise and handling stresses similar to those experienced during salvage operations in the Sacramento-San Joaquin Delta, California, and several recovery environments to assess energetic costs and mortality. Young of the year (2.1-15.9 g wet weight) were exercised in a swim tunnel at a maximum speed of 94 cm/s (11.7-14.1 body lengths/s) for 5 min at 15°C and 25°C and yearlings (30.8-144.7 g) at the same maximum speed (5.5 body lengths/s) and for the same amount of time at 15°C. Using static respirometry, the preexercise and handling (in freshwater), 0-h postexercise and handling, and 2-h postexercise and handling oxygen consumption rates (mg/h) were measured in four recovery treatments: freshwater, brackish water (10‰ NaCl), salt water (30‰ NaCl), and buffered freshwater (10 mM NaHCO₃). Significant increases in 0-h postexercise oxygen consumption rates (compared with the preexercise rates) were followed by significant decreases during recovery, but rates did not fully return to preexercise values within 2 h in young of the year at 25°C or yearlings. No significant differences in metabolism were seen among recovery environment treatments in the same sampling period. Therefore, recovery treatment groups were combined. In the same sampling periods, yearling fish consumed more oxygen than young of the year at the same temperature, with a mass coefficient of 0.72 ± 0.04 (mean ± SE) for young of the year and yearlings at 15°C during the preexercise period. Young of the year at 25°C (combined treatments) had higher metabolic rates than those at 15°C. Buoyancy difficulties and disorientation (which were more exaggerated at 15°C than at 25°C) were observed in young of the year in salt water for up to 2 h following exercise and handling stress, and 45% of the yearling fish in the saltwater treatment died over the subsequent 48 h, presumably from acid-base or ionoregulatory causes. Based on available studies, we recommend that salvaged striped bass be released into brackish water of 3-10‰ salinity to reduce losses that may be caused by screen salvage operations.