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First published online July 6, 2005
Journal of Experimental Biology 208, 2693-2705 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01678

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Alkaline tide and nitrogen conservation after feeding in an elasmobranch (Squalus acanthias)

Chris M. Wood^1,2,3,*, Makiko Kajimura^1,3, Thomas P. Mommsen^3,4 and Patrick J. Walsh^2,3

¹ Department of Biology, McMaster University, 1280 Main St West, Hamilton, Ontario, Canada L8S 4K1
² Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, USA
³ Bamfield Marine Sciences Centre, 100 Pachena Drive, Bamfield, British Columbia, Canada V0R 1B0
⁴ Department of Biology, University of Victoria, Victoria, British Columbia, Canada V8W 2N5

View larger version (19K): [in a new window]   Fig. 1. The influence of (A) the control treatment or (B) experimental feeding on arterial pH (pHa; circles) and venous pH (pHv; triangles) in Squalus acanthias of Series 1. The experimental meal was 20 g of flatfish muscle paste in 20 ml of 140 mmol l–1 NaCl saline per kg dogfish, administered as a bolus down the stomach tube at time 0 h. The control treatment was comparable gastric loading of 40 ml of 140 mmol l–1 NaCl saline per kg dogfish. Values are means ± 1 S.E.M. (N=5). P represents the pre-feeding measurement (horizontal dotted lines). The overall influence of experimental feeding was significant for both pHa and pHv (two-way ANOVA, P x0.05). Within each treatment, means not sharing the same letter are significantly different (one way ANOVA followed by the LSD test). Asterisks indicate significant differences between control and experimental treatments for the same parameter at the same time.

View larger version (17K): [in a new window]   Fig. 2. The influence of (A) the control treatment or (B) experimental feeding on arterial true plasma bicarbonate ([HCO3–]a; circles) and venous true plasma bicarbonate ([HCO3–]v; triangles) concentrations in Squalus acanthias of Series 1. Values are means ± 1 S.E.M. (N=5). Other details as in legend of Fig. 1. The overall influence of experimental feeding was significant for both [HCO3–]a and [HCO3–]v (two-way ANOVA, P x0.05).

View larger version (19K): [in a new window]   Fig. 3. The influence of (A) the control treatment or (B) experimental feeding on arterial CO2 tension (aCO2; circles) and venous CO2 tension (vCO2; triangles) in Squalus acanthias of Series 1. Values are means ± 1 S.E.M. (N=5). (1 torr=0.1333 kPa.) Other details as in legend of Fig. 1. There was no overall significant influence of experimental feeding for either parameter (two-way ANOVA, P>0.05).

View larger version (18K): [in a new window]   Fig. 4. The influence of (A) the control treatment or (B) experimental feeding on arterial O2 tension (aO2; circles) and venous O2 tension (vO2; triangles) in Squalus acanthias of Series 1. Values are means ± 1 S.E.M. (N=5). (1 torr=0.1333 kPa.) Other details as in legend of Fig. 1. There was a significant overall influence of experimental feeding only for vO2 (two-way ANOVA, P x0.05).

View larger version (19K): [in a new window]   Fig. 5. The influence of (A) the control treatment or (B) experimental feeding on the rate of ammonia-N excretion in Squalus acanthias of Series 2. Other details as in legend of Fig. 1. There was a significant overall influence of experimental feeding (two-way ANOVA, P x0.05). There were no significant differences between control and experimental treatments at the same time. Values are means ± 1 S.E.M. Data were taken from those dogfish of Series 2 (control N=5, experimental N=4) where there was no struggling or potential for blood loss from fin abrasion.

View larger version (28K): [in a new window]   Fig. 6. The influence of (A) the control treatment or (B) experimental feeding on the rate of urea-N excretion in Squalus acanthias of Series 2. Values are means ± 1 S.E.M. (control N=5, experimental N=4). Other details as in legends of Figs 1 and 5. There was no significant overall influence of experimental feeding (two-way ANOVA, P>0.05). There were no significant differences between control and experimental treatments at the same time.

View larger version (18K): [in a new window]   Fig. 7. The influence of experimental feeding (triangles) or the control treatment (circles) on (A) plasma urea-N (B) plasma ammonia-N and (C) plasma trimethylamine oxide-N (TMAO-N) concentrations in Squalus acanthias of Series 2. Note the different units (µmol l–1 for ammonia-N versus mmol l–1 for urea-N and TMAO-N). Values are means ± 1 S.E.M. (N=8). Other details as in legend of Fig. 1. There was a significant overall influence of experimental feeding only on plasma ammonia-N (two-way ANOVA, P x0.05) but not on plasma urea-N or TMAO-N.

View larger version (23K): [in a new window]   Fig. 8. The influence of experimental feeding (triangles) or the control treatment (circles) on (A) plasma osmolality and (B) plasma chloride concentration in Squalus acanthias of Series 2. Values are means ± 1 S.E.M. (N=8). Other details as in legend of Fig. 1. There were significant overall influences of experimental feeding on both osmolality and chloride (two-way ANOVA, P x0.05).

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