). Given that metabolic recovery in skeletal muscle (muscle lactate, ATP and glycogen, but not PCr) occurs more rapidly at warm than cold temperatures in exhausted rainbow trout Oncorhynchus mykiss and Atlantic salmon Salmo salar (Kieffer et al., 1994;Wilkie et al., 1997;Kieffer, 2000), the expectation is that swimming performance is restored faster at a higher temperature. This expectation would be consistent with the known increase in both maximum oxygen uptake and maximum cardiac output with temperature (e.g. Butler et al., 1992;Farrell, 1997;Taylor et al., 1997) because an improved oxygen delivery system could support a more rapid recovery of the metabolic debt incurred with exhaustive exercise. However, when Atlantic salmon were angled rather than chased to exhaustion, muscle glycogen, intracellular pH and lactate were restored more rapidly under cold conditions than warm conditions (Wilkie et al., While the temperature dependence of exercise performance in fishes is reasonably well documented, information on the temperature dependence of metabolic recovery and reperformance is scant. This study examined the recovery of swimming performance after exhaustive exercise in rainbow trout Oncorhynchus mykiss at seasonal temperatures ranging from 5 to 17°C and explored the relationship between performance and preceding metabolic state. The primary objective of the study was to test the hypothesis that increased temperature increases the capability of rainbow trout to repeat a critical swimming speed (U crit), as assessed by two consecutive critical swimming speed tests separated by a 40·min rest interval. An additional expectation was that certain plasma ionic, metabolic and humoral parameters would be correlated with how well fish reperformed and so plasma levels of lactate, potassium, ammonia, osmolality, sodium and cortisol, as well as hematocrit, were monitored before, during and after the swim challenges via an indwelling cannula in the dorsal aorta. As expected, performance in the first Ucrit test (Ucrit1) was positively related to temperature. However, the relationship between Ucrit1 and reperformance (Ucrit2) was not dependent on acclimation temperature in a simple manner. Contrary to our expectations, Ucrit2 was less than Ucrit1 for warmacclimated fish (14.9±1.0°C), whereas Ucrit2 equaled Ucrit1 for cold-acclimated fish (8.4±0.9°C). Cold-acclimated fish also exhibited a lower Ucrit1 and less metabolic disruption compared with warm-acclimated fish. Thus, while warm acclimation conferred a faster Ucrit1, a similar swimming speed could not be attained on subsequent swim after a 40·min recovery period. This finding does not support the hypothesis that the ability of rainbow trout to reperform on U crit test is improved with temperature. Both plasma lactate and plasma potassium levels were strongly correlated with Ucrit1 performance. Therefore, the higher Ucrit1 of warm-acclimated fish may have been due in part to a greater anaerobic swimming effort compared with cold-acclimated fish. In fact, a significant co...

No abstract

Measurements of swimming ability, such as critical swimming speed (Ucrit), have commonly been used as indicators of the effects of environmental challenges on the general health of fish. In this study, we introduce repeat swimming performance as a particularly sensitive means to assess fish health and the effects of environmental stressors. Adult sockeye salmon (Oncorhynchus nerka) performed two Ucrit tests separated by a 40-min recovery period. When recovery ability was expressed as a ratio of Ucrit values in the first and second swim challenges (Ucrit,2/Ucrit,1), control fish exhibited recovery ratios of unity (0.98 ± 0.01 (mean ± SEM)). In contrast, the recovery of fish pre-exposed to between 0.12 and 0.77 mg·L-1 dehydroabietic acid (DHA) for 8-14 h, and swimming in either hypoxia or normoxia, was impaired. These fish had recovery ratios significantly lower than unity (0.92 ± 0.02) despite swimming to a similar initial Ucrit as control fish. The effect of pre-exposure to DHA was also evident in measurements of oxygen consumption and plasma lactate concentration. Unhealthy fish exhibited significantly lower initial and second Ucrit values than control fish. To account for the low initial swimming performance of these fish, a normalized recovery ratio was introduced ((Ucrit,1/Ucrit,1(control) + Ucrit,2/Ucrit,1)/2). This index of recovery (0.65 ± 0.08) identified the poor physical status of these fish.

Numerous studies have examined the effect of temperature on in vivo and in situ cardiovascular function in trout. However, little information exists on cardiac function at temperatures near the trout's upper lethal limit. This study measured routine and maximum in situ cardiac performance in rainbow trout (Oncorhynchus mykiss) following acclimation to 15, 18 and 22 °C, under conditions of tonic (30 nmol l-1), intermediate (60 nmol l-1) and maximal (200 nmol l-1) adrenergic stimulation. Heart rate increased significantly with both temperature and adrenaline concentration. The Q10 values for heart rate ranged from 1.28 at 30 nmol l-1 adrenaline to 1.36 at 200 nmol l-1 adrenaline. In contrast to heart rate, maximum stroke volume declined by approximately 20 % (from 1.0 to 0.8 ml kg-1) as temperature increased from 15 to 22 °C. This decrease was not alleviated by maximally stimulating the heart with 200 nmol l-1 adrenaline. Because of the equal and opposite effects of increasing temperature on heart rate and stroke volume, maximum cardiac output did not increase between 15 and 22 °C. Maximum power output decreased (by approximately 10-15 %) at all adrenaline concentrations as temperature increased. This reduction reflected a poorer pressure-generating ability at temperatures above 15 °C. These results, in combination with earlier work, suggest (1) that peak cardiac performance occurs around the trout's preferred temperature and well below its upper lethal limit; (2) that the diminished cardiac function concomitant with acclimation to high temperatures was associated with inotropic failure; (3) that Q10 values for cardiac rate functions, other than heart rate per se, have a limited predictive value at temperatures above the trout's preferred temperature; and (4) that heart rate is a poor indicator of cardiac function at temperatures above 15 °C.