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- McArley, Tristan J., et al.
(author)
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Experimental hyperoxia (O-2 supersaturation) reveals a gill diffusion limitation of maximum aerobic performance in fish
- 2022
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In: Biology Letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 18:11
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Journal article (peer-reviewed)abstract
- Several studies have demonstrated that hyperoxia increases the maximal O-2 consumption rate (<(M) over dot>O-2max) in fish, but exactly how this occurs remains to be explained. Here, we tested the hypothesis that hyperoxia improves arterial oxygenation in rainbow trout during exhaustive exercise. We demonstrate a 35% higher <(M) over dot>O-2max in hyperoxia (200% air saturation) relative to normoxia, which was achieved through a combined 15% increase in cardiac output due to elevated peak heart rate, and a 19% increase of the arterial-venous (A-V) O-2 content difference. While arterial O-2 partial pressure (PaO2) and O-2 saturation of haemoglobin declined post-exhaustive exercise in normoxia, this did not occur in hyperoxia. This protective effect of hyperoxia on arterial oxygenation led to a 22% higher arterial O-2 content post-exhaustive exercise, thereby allowing a higher A-V O-2 content difference. These findings indicate that <(M) over dot>O-2max is gill diffusion limited in exhaustively exercised rainbow trout. Moreover, as previous studies in salmonids have demonstrated collapsing PaO2 in normoxia at maximal swimming speed and at acutely high temperatures, a diffusion limitation may constrain <(M) over dot>O-2 in other situations eliciting peak metabolic demand. These findings, along with the fact that hyperoxia increases <(M) over dot>O-2max in several other fishes, suggest that gill diffusion limitations of <(M) over dot>O-2max may be widespread in fishes.
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| 2. |
- Mendoza, P., et al.
(author)
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Starch and fiber intake effects on energy metabolism, growth, and carapacial scute pyramiding of red-footed tortoise hatchlings (Chelonoidis carbonaria)
- 2022
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In: Comparative Biochemistry and Physiology a-Molecular & Integrative Physiology. - : Elsevier BV. - 1095-6433. ; 265
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Journal article (peer-reviewed)abstract
- Tortoise husbandry includes reports of excessive growth and carapace pyramiding, although triggers still remain to be fully elucidated. Juvenile red-footed tortoises (Chelonoidis carbonaria) were fed with two different diets, one high in fiber (HF; 14.2% crude fiber; 39.2% neutral detergent fiber, NDF; dry matter basis, DMB) and one high in starch (HS; 27.7% DMB), to assess effects on energy metabolism, nutrient digestibility, and growth. A total of 20 hatchlings (10 per diet) were used to evaluate: apparent digestibility coefficients (Da) of nutrients and gross energy (GE), passage times at 5 and 11 months of age; resting and post-prandial metabolic rates at 6 and 12 months of age; growth rates; pyramiding; and estimated body composition. Animals fed HS showed higher mass-specific intake of digestible energy (113.9 +/- 32.1 kJ kg(-1) day(-1) vs. 99.6 +/- 35.3 kJ kg(-1) day(-1); P < 0.05), digestible DM (6.1 +/- 1.8 g kg(-1) day(-1) vs. 5.0 +/- 1.8 g kg(-1) day(-1); P < 0.01), shorter transit (3 +/- 1 days vs. 4 +/- 1 days; P < 0.01) and retention times (8 +/- 2 days vs. 10 +/- 2 days; P < 0.01), and higher Da of DM, starch, NDF, and GE. Crude protein Da was higher for HF. Rest and post-prandial metabolic rates, and pyramiding degree were not affected by diets. At 13 months, the animals from HS presented wider plastrons and carapaces, and higher carapace width growth rates. In addition, these animals had lower body mineral content (1.88 +/- 0.15% vs. 2.15 +/- 0.19%; P < 0.01) and bone density (0.13 +/- 0.01 g mm(-2) vs. 0.15 +/- 0.02 g mm(-2); P < 0.02). Results provide evidence that highly digestible foods can accelerate shell growth and lower mineralization in this species.
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