title: Physiological adaptations of the gut in the Lake Magadi tilapia, Alcolapia grahami, an alkaline- and saline-adapted teleost fish.
abstract: We describe the gut physiology of the Lake Magadi tilapia (Alcolapia grahami), specifically those aspects associated with feeding and drinking while living in water of unusually high carbonate alkalinity (titratable base=245 mequiv l(-1)) and pH (9.85). Drinking of this highly alkaline lake water occurs at rates comparable to or higher than those seen in marine teleosts. Eating and drinking take place throughout the day, although drinking predominates during hours of darkness. The intestine directly intersects the esophagus at the anterior end of the stomach forming a 'T', and the pyloric sphincter, which comprises both smooth and striated muscle, is open when the stomach is empty and closed when the stomach is full. This unique configuration (a functional trifurcation) allows imbibed alkaline water to bypass the empty stomach, thereby avoiding a reactive mixing with acidic gastric fluids, and minimizes interference with a full stomach. No titratable base was present in the stomach, where the mean pH was 3.55, but the intestine was progressively more alkaline (foregut 6.96, midgut 7.74, hindgut 8.12, rectum 8.42); base levels in the intestinal fluid were comparable to those in lake water. The gut was highly efficient at absorbing water (76.6%), which accompanied the absorption of Na(+) (78.5%), titratable base (80.8%), and Cl(-) (71.8%). The majority of Na(+), base and water absorption occurred in the foregut by an apparent Na(+) plus base co-transport system. Overall, more than 70% of the intestinal flux occurred via Na(+) plus base co-transport, and less than 30% by Na(+) plus Cl(-) co-transport, a very different situation from the processes in the intestine of a typical marine teleost.
authors: Department of Zoology and Physiology, University of Wyoming, Laramie, WY, 82071, USA.
authors: Annie Narahara
authors: AN
authors: Bergman
authors: Pierre
authors: P
authors: Laurent
authors: George
authors: G
authors: Otiang'a-Owiti
authors: Harold L
authors: HL
authors: Bergman
authors: Patrick J
authors: PJ
authors: Walsh
authors: Paul
authors: P
authors: Wilson
authors: Chris M
authors: CM
authors: Wood
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects* / Q000502:physiology*; D000818:Animals; D001692:Biological Transport; D004327:Drinking Behavior / Q000502:physiology; D004777:Environment; D005247:Feeding Behavior / Q000502:physiology; D005618:Fresh Water; D005766:Gastrointestinal Contents; D041981:Gastrointestinal Tract / Q000187:drug effects / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007422:Intestines / Q000187:drug effects / Q000502:physiology; D007630:Kenya; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D017210:Tilapia / Q000502:physiology*
chemical_list: D012965:Sodium Chloride