• White, Alaina
  • Schreer, Jason F.
  • Cooke, Steven J.


Two of the major stressors associated with the catch-and-release of recreationally angled fish are exercise and air exposure. This study investigated the combined effects of exercise and air exposure duration on the congeneric largemouth bass Micropterus salmoides and smallmouth bass M. dolomieu, two of the most popular sportfish in North America. We simulated angling by exercising the fish (i.e., chasing by hand) for either 20 or 180 s and then immediately exposed fish to air for random durations ranging from 0 to 10 min. To assess the combined effects of increased exercise and air exposure durations, and the time needed to recover, we monitored several behavioral responses for both species. For largemouth bass, we also measured hematological variables (i.e., lactate, glucose, and hematocrit). Never did exercise and air exposure have a significant effect on the same response measured in the same species, suggesting that there are two separate responses occurring: likely an exercise response and a stress response associated with hypoxia. Our results also indicate that largemouth bass recover from combined exercise and air exposure faster than smallmouth bass. Smallmouth bass took longer to regain equilibrium, to stop leaning, and to return to very shallow (i.e., normal) ventilation depth, as a result of the treatments of exercise and air exposure, than the largemouth bass. This is likely due in part to behavioral and habitat differences between the two species as well as their different aerobic capacities and sensitivities to hypoxia. Interestingly, no mortality was observed despite air exposure durations of up to 10 min. It is still unclear how air exposure interacts with environmental stressors, such as water temperature. We conclude, based on these findings and as suggested from other studies, that air exposure is a significant stressor, and that species-specific guidelines are needed for catch-and-release practices to be most effective, and to best insure the sustainability of fisheries.


Study site and animals

This study was conducted in June of 2006 at the Queen's University Biological Station on Lake Opinicon, in Elgin, Ontario (44°31′N, 76°20′W). All fish were collected from Lake Opinicon by anglers using rod and reels and landed within 20 s to minimize physiological disturbance (Kieffer, 2000). Following capture, fish were held in coolers filled with lake water which was changed frequently (at least every 10 min) and all fish were delivered to an indoor wet lab facility within 1 h. Fish were held for at least 24 h prior to experimentation in flow-through tanks (approximately 200 L) provided with lake water. For experiments done using behavioral sampling, largemouth bass (n = 56) ranged in size (total length) from 231 to 445 mm (mean total length ± standard error, 331 ± 7.5 mm) and smallmouth bass (n = 21) ranged from 238 to 432 mm (307 ± 12.9 mm). During behavioral assessments for largemouth bass, water temperatures ranged from 18 to 23 °C and water temperatures ranged from 19 to 22 °C for smallmouth bass. These temperatures are considered moderate for both species (Armour, 1993). Hematological experiments were restricted to largemouth bass (n = 46), which ranged in size (total length) from 266 to 443 mm (345 ± 7.1 mm) at water temperatures of 20–21 °C.

Behavioral sampling

Daily, eight largemouth and/or smallmouth bass were moved from common holding tanks to individual tanks (200 L flow-though tanks divided into four sections with porous foam dividers) and held overnight (at least 12 h). Laboratory access was restricted to prevent external disturbance during all experimentation. During the move, each fish was placed in a padded V-shaped holder filled with lake water, where total length was measured and a dorsal spine was clipped for identification. The next morning, resting ventilation rates (per minute) for each fish were measured, by counting operculum movements over 30 s and multiplying by 2, as was depth of ventilation or operculum movements (very shallow, shallow, medium, or deep). Also recorded was whether or not each fish had equilibrium, was leaning/unsteady, and was parallel to the bottom, meaning that the fish was level in the water column, rather than tail lower or higher than head. All eight fish were then simultaneously exposed to different treatments of exercise followed by various air exposures. To simulate brief or exhaustive exercise, fish, while in their individual flow-through tanks, were chased by hand for either 20 or 180 s, an approach frequently used for catch-and-release research, especially to assess the effects of exercise (Kieffer, 2000, Cooke et al., 2001, Cooke et al., 2003, Suski et al., 2004, Schreer et al., 2005). Following exercise, each fish was immediately held out of the water, by inserting a thumb into their mouth and gripping the lower jaw, for a randomly generated time (generated in SPSS 12.0 (September 2003)) from 0 to 10 min (to the nearest second). Although the 10 min period might seem excessive, it was intended to account for lengthy hook removal followed by measuring, weighing, pictures, etc. After treatment, the fish were replaced into their individual flow-through tanks and monitored for 9 h. All responses were measured immediately and again every 10 min for 3 h, and again at 5 and 9 h. During the first 10 min, the fish were observed continuously and the time of any changes in the responses, besides ventilation rate, were recorded. After 9 h the fish were moved to an outdoor flow-through holding tank (approximately 500 L) until the next morning (24 h post-treatment), to assess delayed mortality, and were then released back into Lake Opinicon.