Physiological Effects of Brief Air Exposure in Exhaustively Exercised Rainbow Trout (Oncorhynchus mykiss): Implications for "Catch and Release" Fisheries

Abstract

Rainbow trout (Oncorhynchus mykiss) which were air exposed for 60 s after exhaustive exercise initially had a much larger extracellular acidosis than trout which were only exercised. In both groups, however, plasma pH returned to normal by 4 h. Blood lactate concentrations were also greater in the air-exposed fish and continued to increase throughout the experiment. During air exposure, there was retention of carbon dioxide in the blood, and oxygen tension (Po2) and hemoglobin:oxygen carriage (Hb:O2) both fell by over 80%. After 30 min of recovery, however, blood gases resembled those in fish which were only exercised. Finally, survival after 12 h was 10% in control fish and 88% in the exercised fish but fell to 62 and 28% in fish which were air exposed for 30 and 60 s, respectively, after exercise. These results indicate that the brief period of air exposure which occurs in many "catch and release" fisheries is a significant additional stress which may ultimately influence whether a released fish survives.

Physiological response of wild rainbow trout to angling: impact of angling duration, fish size, body condition, and temperature

“…Although the range of baseline and elevated levels vary by study from possible factors such as temperature and genetic differences, results from each study consistently demonstrated that the physiological disturbance increased with the duration of stress or exercise. Handling stress has also been demonstrated to cause significant physiological disruptions (Pickering and Pottinger, 1989;Ferguson and Tufts, 1992), and handling stress during the hook removal process is a concern among researchers examining the response of fish to angling (Cooke et al, 2001). We suggest that the initial slope of increase for levels of plasma cortisol and lactate in extended capture fish following landing and handling stress represents the early stages of a stress response that will continue to increase.…”

“…Once a fish was hooked, other anglers stopped fishing and assisted with the sampling procedure, thus maintaining similar fishing effort. Handling time (hook removal) began when a fish was netted after landing until the angler removed the hook, and anglers were instructed to keep fish under water during the handling portion of capture to avoid any associated mortality due to air exposure (Bouck and Ball, 1966;Ferguson and Tufts, 1992). Anglers were instructed to land fish as they normally would while fishing recreationally, but not to play fish to exhaustion.…”

“…angling duration) on physiological parameters were combined because both exhaustive exercise and handling stress have been shown to cause physiological changes in rainbow trout, and it was not feasible to separate their effects in this study (Pickering and Pottinger, 1989;Ferguson and Tufts, 1992). The amount of time fish were anesthetized in clove oil and sampled for blood under anesthesia was not included in analysis of the elevation of blood parameters because it was relatively short and similar for all fish (mean minutes:seconds ± S.E., anesthesia 2:08 ± 0:06, blood sampling 1:23 ± 0:05).…”

“…In addition, it has been demonstrated that the immediate physiological response by rainbow trout exposed to clove oil is minimal with short exposure times and most likely reflects stress prior to anesthesia (Wagner et al, 2002). Thus, landing time and the time required to remove hooks were considered to be the most influential to any physiological changes, due to the physically exhaustive nature of both stressors (Ferguson and Tufts, 1992;Booth et al, 1995). Fish were separated into rapid and extended capture groups because it has been demonstrated that physiological changes can occur within a few minutes after the onset of a stressor, therefore, the levels of blood parameters for rapid capture fish would potentially reflect the levels of free-swimming fish (Wydoski et al, 1976;Pankhurst and Dedual, 1994).…”

“…Recent studies have also addressed the effect of hook type on the ease of removal and handling time by comparing various hook types, such as circle versus standard "J" hooks and barbed versus barbless hooks (e.g., Cooke et al, 2001Cooke et al, , 2003, and by measuring the physiological response to air exposure, which commonly occurs during the hook removal process (Ferguson and Tufts, 1992;Cooke et al, 2001). …”