SUMMARYThe mechanism underlying the decrease in aerobic scope in fish at warm temperatures is not fully understood and is the focus of this research. Our study examined oxygen uptake and delivery in resting, swimming and recovering sockeye salmon while water temperature was acutely increased from 15°C to 24°C in 2°C h -1 increments. Fish swam at a constant speed during the temperature change. By simultaneously measuring oxygen consumption (M O2 ), cardiac output (Q) and the blood oxygen status of arterial and venous blood, we were able to determine where in the oxygen cascade a limitation appeared when fish stopped sustained swimming as temperature increased. High temperature fatigue of swimming sockeye salmon was not a result of a failure of either oxygen delivery to the gills or oxygen diffusion at the gills because oxygen partial pressure (P O2 ) and oxygen content (C O2 ) in arterial blood did not decrease with increasing temperature, as would be predicted for such limitations. Instead, arterial oxygen delivery (Ta O2 ) was initially hampered due to a failure to adequately increase Q with increasing temperature. Subsequently, lactate appeared in the blood and venous P O2 remained constant.

No abstract

Oxygen consumption (M O2 ) was measured for gilthead seabream (Sparus aurata) during spontaneous and forced activities. During spontaneous activity, the swimming pattern was analysed for the effect on M O2 on the average speed (U), turning rate () and change in speed (DU). All swimming characteristics contributed significantly to the source of spontaneous swimming costs, and the models explained up to 58% of the variation in M O2 : Prediction of M O2 of fish in field studies can thereby be improved if changes in speed and direction are determined in addition to swimming speed. A relationship between swimming speed and M O2 during forced activity was also established. During spontaneous activity, 2.5 times more energy was used than in forced swimming at a speed of 0.5 BL s À1. This indicates that spontaneous swimming costs may be considerably higher compared with those of a fixed swimming speed. However, comparing M O2 at the respective optimum swimming speeds with the lowest cost of transport (U opt ) resulted in similar values independent of swimming mode. This could be an important observation in estimating energetic costs of free-ranging fishes.

Decreased critical swimming speed and increased oxygen consumption (M O2 ) was found for externally tagged Atlantic cod Gadus morhua swimming at a high speed of 0Á9 body length (total length, L T ) s À1 . No difference was found in the standard metabolic rate, indicating that the higher M O2 for tagged cod was due to drag force rather than increased costs to keep buoyancy.

While it is well known that O2 is directly removed from the water by skin and gill tissues of fish, the mismatch between O2 removal from water (O2 uptake; [Formula: see text]) and the O2 delivered to tissues by the primary circulation (O2 consumption; [Formula: see text]) has never been measured directly. Using data from four recent studies that simultaneously measured [Formula: see text] and [Formula: see text] in 2-5 kg Pacific salmon, our analysis revealed that sockeye salmon can remove an additional 12-48 % more O2 from the water than the primary circulation delivers to the systemic tissues. This percentage did not change significantly during swimming activity, a result that contradicts an earlier prediction that the difference should decrease when [Formula: see text] increases during exercise. In resting Chinook salmon, a similar percentage difference in simultaneously measured [Formula: see text] and [Formula: see text] was observed, yet the difference tended to disappear during acute heat stress to a near lethal temperature. These results emphasize that caution should be exercised when using the Fick equation to estimate cardiac output because the overestimate of cardiac output that results from using the Fick equation in Pacific salmon is not small, may not be fixed and may exist in other teleosts.

This study reports the first results on telemetry of caudal differential pressure during spontaneous swimming activity in cod Gadus morhua and demonstrates that tail-beat pressure may be used as a predictor of activity and swimming costs of free-swimming cod. Tail-beat pressure was monitored using a differential pressure sensor on the caudal peduncle of cod and spontaneous swimming activity was quantified using a customized video-computer tracking programme. Tail-beat pressure was found to correlate with (1) swimming speed (U) and oxygen consumption ðM O2 Þ during forced swimming and (2) mean U during spontaneous activity. Based on the relationship between M O2 and the integrated pressure performed by the tail during forced swimming, it should be possible to predict M O2 during spontaneous activity. To gain precise measures of activity and thus predictions of M O2 for free-swimming fish, however, individual calibrations are necessary.

No abstract

2005) Does temperature preference relate to the anaerobic capacity of Atlantic cod (Gadus morhua L.) with different haemoglobin phenotype?, Marine Biology Research, 1:6, 411-416, AbstractThe effect of Hb-I* phenotype on white muscle lactate dehydrogenease (LDH, E. C. 1.1.1.27) activity and buffering capacity was studied in Atlantic cod (Gadus morhua ), acclimated and measured at temperatures near their behavioral temperature preference. It was hypothesized that these conditions would optimize biochemical processes but no difference was found in LDH activity between the Hb-I* phenotype after 56 d of acclimation to 6 and 148C. However, LDH activity was both mass-and temperature-dependent; mean activity was 162.29/5.0 and 275.99/6.4 IU g (1 wet mass (mean9/SEM) at 6 and 148C respectively and larger fish had the highest rate of enzyme activity. White muscle buffer capacity was unaffected by Hb-I* phenotype but higher in cod held at 148C.