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First published online March 31, 2007
Journal of Experimental Biology 210, 1335-1349 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02736

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Osmoregulation, ionoregulation and acid–base regulation by the gastrointestinal tract after feeding in the elasmobranch (Squalus acanthias)

Chris M. Wood^1,2,3,*, Makiko Kajimura^1,3, Carol Bucking^1,3 and Patrick J. Walsh^2,3,4

¹ Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, L8S 4K1, Canada
² Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, FL 33149, USA
³ Bamfield Marine Sciences Centre, 100 Pachena Drive, Bamfield, British Columbia, Canada
⁴ Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, Ontario, K1N 6N5, Canada

View larger version (31K): [in this window] [in a new window]   Fig. 1. The influence of feeding on the relative mass of the tissue (expressed as g kg–1 body mass) of various segments of the gastrointestinal tract in the dogfish shark – (A) stomach-1 (cardiac stomach), (B) stomach-2 (pyloric stomach) and (C) intestine. The inset bars indicate the mass contributed by the tissue water content, and the differences represent the mass contributed by the tissue dry-matter content. Means ± 1 s.e.m. (N=6–8 at each time point). Means not sharing the same letter are significantly different (P<0.05); the same symbols apply to the mass contributed by tissue water content and so have not been repeated.

View larger version (5K): [in this window] [in a new window]   Fig. 2. The influence of feeding on plasma total CO2 concentration in blood samples drawn by caudal puncture in the dogfish shark. Means ± 1 s.e.m. (N=6–8 at each time point). Means not sharing the same letter are significantly different (P<0.05).

View larger version (10K): [in this window] [in a new window]   Fig. 3. The influence of feeding on the pH of the fluid phase of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach), intestine and colon in the dogfish shark. Means ± 1 s.e.m. (N=6–8 at each time point). Within a compartment, means not sharing the same letter are significantly different (P<0.05).

View larger version (9K): [in this window] [in a new window]   Fig. 4. The influence of feeding on total water volumes (expressed as ml kg–1 body mass) of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine in the dogfish shark. This measurement includes water in both the fluid and solid phases. Means ± 1 s.e.m. (N=6–8 at each time point). Within a compartment, means not sharing the same letter are significantly different (P<0.05).

View larger version (19K): [in this window] [in a new window]   Fig. 5. The influence of feeding on (A) the osmolality and (B) the urea concentration of the fluid phases of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine in the dogfish shark. Simultaneously measured values in the blood plasma are also shown. Means ± 1 s.e.m. (N=6–8 at each time point). As points of reference, the dark bars represent the measured values for ambient seawater (SW) (N=4), and the light bars represent the estimated value for the ingested food [N=5; value for osmolality from Holmes and Donaldson (Holmes and Donaldson, 1969)]. Significant differences are not marked in A so as to avoid clutter; the only significant differences (P<0.05) within compartments are in plasma osmolality, as indicated by means not sharing the same letter in the following series: a=6 h, 30 h, 360 h; b=20 h, 120 h, 360 h; c=20 h, 60 h, 120 h. In B, within a compartment, means not sharing the same letter are significantly different (P<0.05). For clarity, x,y refers to stomach-2 and a,b to stomach-1.

View larger version (29K): [in this window] [in a new window]   Fig. 6. The influence of feeding on (A) sodium, (B) chloride and (C) potassium concentrations of the fluid phases of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine in the dogfish shark. Simultaneously measured values in the blood plasma are also shown. Means ± 1 s.e.m. (N=6–8 at each time point). As points of reference, the dark bars represent the measured values for ambient seawater (SW) (N=4), and the light bars represent the measured values for the ingested food (N=5). Within a compartment, means not sharing the same letter are significantly different (P<0.05). There were no significant differences in the plasma compartment in A–C. In C, for clarity, x,y,z refers to stomach-2 and a,b,c to stomach-1.

View larger version (19K): [in this window] [in a new window]   Fig. 7. The influence of feeding on (A) Ca and (B) Mg concentrations of the fluid phases of the gastrointestinal contents in stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine in the dogfish shark. Simultaneously measured values in the blood plasma are also shown. Means ± 1 s.e.m. (N=6–8 at each time point). As points of reference, the dark bars represent the measured values for ambient seawater (SW) (N=4), and the light bars represent the measured values for the ingested food (N=5). Within a compartment, means not sharing the same letter are significantly different (P<0.05). There were no significant differences in the plasma compartment in A. In B, for clarity, x,y refers to stomach-2 and a,b to stomach-1.

View larger version (14K): [in this window] [in a new window]   Fig. 8. The influence of feeding on the composition of gall bladder bile in the dogfish shark. Means ± 1 s.e.m. (N=6–8 at each time point). For each parameter, means not sharing the same letter are significantly different (P<0.05). There were no significant differences for K+.

View larger version (32K): [in this window] [in a new window]   Fig. 9. A comparison of the summation of total measured osmolytes in the blood plasma and the fluid phases of stomach-1 (cardiac stomach), stomach-2 (pyloric stomach) and intestine prior to feeding (A) and at 20 h post-feeding (B). Arrows indicate measured osmolalities. (A) Prior to feeding, note the reasonable agreement between total measured osmolytes and measured osmolality in blood plasma, stomach-1 and stomach-2, but not in intestine. (B) After feeding, note continued agreement in blood plasma, but the discrepancies in all three gastrointestinal fluids. Note also the different contributions of urea versus Na++Cl– in the various compartments.