Oxygen removal from water versus arterial oxygen delivery: calibrating the Fick equation in Pacific salmon

Abstract

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.

Cardiac oxygen limitation during an acute thermal challenge in the European perch: effects of chronic environmental warming and experimental hyperoxia

“…Such increases in PvO 2 with warm acclimation are likely caused by a combination of thermally compensated metabolic rate and tissue oxygen extraction, as observed previously in the warm-acclimated Biotest perch (48), and a right-shift in the oxygen-hemoglobin dissociation curve (46). The PvO 2 in the reference fish exposed to ambient hyperoxia was maintained at a significantly elevated level throughout the thermal challenge, which was most likely the result of increased oxygen diffusion at the gills, and possibly increased cutaneous oxygen diffusion (25,33). Interestingly, there was a sharp drop in PvO 2 in the hyperoxic group at 28°C that occurred just prior to the onset of the decline in heart rate.…”

“…Again, the underlying cause for this dramatic metabolic response in hyperoxia is presently unknown. The relative importance of cutaneous oxygen uptake has been suggested to decrease with increasing temperature in salmonid fish (25), and so another fascinating possibility is that the sharp drop in PvO 2 could be at least partly explained by a sudden decrease in cutaneous blood perfusion at temperatures approaching CT max .…”

“…No significant differences were found between the experimental groups. (25). Briefly, a small incision was made in the left cleithrum, and the ductus of Cuvier was exposed using blunt dissection.…”

Experimental manipulations of tissue oxygen supply do not affect warming tolerance of European perch

“…Asterisks in B indicate a significant difference (P<0.05) from the control group. (Glover et al, 2013), increases in the utilization of the secondary circulatory system (Farrell et al, 2014) and/or maintaining a large diffusion gradient between the blood and tissues (due to an elevated partial pressure of oxygen in the venous system). Nevertheless, it is clear that the greatly increased ṀO 2 of hyperoxic fish at temperatures directly preceding CT max did not result in a significantly elevated acute upper thermal limit.…”

Cardiorespiratory upregulation during seawater acclimation in rainbow trout: effects on gastrointestinal perfusion and postprandial responses

“…A previous study on rainbow trout acutely exposed to seawater used the Fick equation and estimated that cardiac output (CO) increased by 30%, primarily via an increase in cardiac stroke volume (SV) (27). However, beyond the problems of estimating CO in fish with the Fick equation (15), Maxime et al (27) only examined circulatory responses for 24 h following seawater transfer. Therefore, it remains unresolved whether prolonged exposure to seawater results in a chronically elevated CO that may explain the increased gastrointestinal perfusion or whether there is also a redistribution of blood flow due to regional changes in vascular resistance.…”