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

Chris M. Wood, Makiko Kajimura, Carol Bucking, Patrick J. Walsh

Research output: Contribution to journalArticle

50 Citations (Scopus)

Abstract

In order to study the physiological consequences of voluntary feeding in the gastrointestinal tract of a ureotelic marine elasmobranch, dogfish (fasted for 96 h) were sampled at various times up to 360 h after consuming a 5-6% ration of teleost fish (hake) under natural feeding conditions. Digestion and absorption were completed between 120 and 360 h post-feeding. The tissue masses of different segments of the gastrointestinal tract increased and decreased markedly as the chyme moved through, mainly because of fluid engorgement rather than hyperplasia. In fasted dogfish, the cardiac and pyloric stomachs contained only small volumes of highly acidic fluid (pH 1.77±1.12, 2.05±0.08) similar in composition to seawater. Feeding resulted in gastric pHs of 3.20±0.31 and 3.95±0.40 at 6 h, followed by slow declines through 60 h. An alkaline tide in the blood also occurred at 6 h. In the face of large changing masses of highly acidic chyme in the stomachs, the pH (6.50±0.10), ionic composition and volume of chyme in the intestine (spiral valve) were precisely regulated from 6 to 60 h post-feeding at very different values from those in the stomachs, and intestinal HCO3 - remained low (5.12±0.83 mmol l-1). The colon was usually empty and its pH constant at 7.20±0.16 at all times. Despite the ingestion of strongly hypo-osmotic teleost tissue, the osmolality of the chyme remained in equilibrium with that of the blood plasma in all segments at all times after feeding. Much of the osmotic equilibration was because of the secretion of urea into the chyme, particularly in the intestine. After feeding, gastric fluid concentrations of Na+ and Mg2+ declined, K+ and Ca2+ increased, whereas Cl- exhibited little change, indicating that additional drinking of seawater was minimal. Na+, K+, water and especially Cl- were absorbed in the intestine, whereas Mg2+ and Ca2+ were largely excluded. Our results illustrate the complex integration of digestive and ionoregulatory function in the elasmobranch digestive tract, and marked differences from the teleost pattern.

Original languageEnglish
Pages (from-to)1335-1349
Number of pages15
JournalJournal of Experimental Biology
Volume210
Issue number8
DOIs
StatePublished - Apr 1 2007

Fingerprint

Squalus acanthias
Elasmobranchii
Osmoregulation
osmoregulation
gastrointestinal system
Gastrointestinal Tract
Stomach
stomach
Acids
Dogfish
acids
acid
Intestines
intestines
Seawater
teleost
seawater
calcium
engorgement
fluid

Keywords

  • Alkaline tide
  • Chyme composition
  • Dogfish
  • Gastric acid secretion
  • Osmolality
  • Shark
  • Urea

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Agricultural and Biological Sciences (miscellaneous)

Cite this

Osmoregulation, ionoregulation and acid-base regulation by the gastrointestinal tract after feeding in the elasmobranch (Squalus acanthias). / Wood, Chris M.; Kajimura, Makiko; Bucking, Carol; Walsh, Patrick J.

In: Journal of Experimental Biology, Vol. 210, No. 8, 01.04.2007, p. 1335-1349.

Research output: Contribution to journalArticle

Wood, Chris M. ; Kajimura, Makiko ; Bucking, Carol ; Walsh, Patrick J. / Osmoregulation, ionoregulation and acid-base regulation by the gastrointestinal tract after feeding in the elasmobranch (Squalus acanthias). In: Journal of Experimental Biology. 2007 ; Vol. 210, No. 8. pp. 1335-1349.
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