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First published online September 19, 2006
Journal of Experimental Biology 209, 3777-3785 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02442
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Feeding and digestion in low salinity in an osmoconforming crab, Cancer gracilis II. Gastric evacuation and motility

Iain J. McGaw

School of Life Sciences, University of Nevada, Las Vegas, NV 89154-4004, USA and Bamfield Marine Sciences Centre, Bamfield, British Columbia, VOR 1BO, Canada


Figure 1
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  		Fig. 1. Methodology for quantifying food processing in the foregut. Large contractions were counted as (A) opening and (B) closing of the gastric mill apparatus and relaxation and contraction of the cardiac sac. Minor gut contractions were quantified as (C) relaxation and (D) contraction of the pyloric region of the foregut.

 

Figure 2
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  		Fig. 2. Passage of digesta through the foregut, midgut and hindgut regions of 10 Cancer gracilis maintained in (A) 100%SW, (B) 80%SW and (C) 60%SW. Values represent means ± s.e.m. In some cases standard errors were small and do not show clearly on the graphs.

 

Figure 3
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  		Fig. 3. Radiographs showing passage of digesta through the gut system of Cancer gracilis in 100%SW, 80%SW and 60%SW. The foregut appears as a heart shaped mass in the upper portion of each radiograph. Digesta then passes into the midgut region, and finally appears in coil formation in the hindgut.

 

Figure 4
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  		Fig. 4. Radiographs showing the regurgitation of food from the stomach of a Cancer gracilis in 60%SW. The boundaries of the foregut and oesophagus are shown. (A,B) The cycle starts with a relaxation of the foregut (C,D), followed by a strong contraction of the cardiac sac (solid arrows). (E,F) Increasing waves of contraction expel food up and out of the oesophagus (dotted arrows).

 

Figure 5
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  		Fig. 5. Mean times (± s.e.m.) for emptying of the foregut, midgut and hindgut of 10 Cancer gracilis maintained in 100%SW, 80%SW and 60%SW.

 

Figure 6
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  		Fig. 6. Gut contraction rates (mean ± s.e.m.) of 10 Cancer gracilis measured at various times after change of salinity to 100%SW, 80%SW and 60%SW. (A) Contractions of the cardiac sac and gastric mill. (B) Contractions of the pyloric stomach region.

 

Figure 7
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  		Fig. 7. (A) Passage of digesta through the foregut, midgut and hindgut and (B) gut contraction rates in 10 Cancer gracilis exposed to a salinity cycle. Crabs were fed in 100%SW and allowed to digest the food for 3 h. The salinity was then lowered to 65%SW for 6 h, before being raised back up to 100%SW.

 




© The Company of Biologists Ltd 2006