Variations in gastric acid secretion during periods of fasting between two species of shark

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Vol. 141; no. 2; pp. 210 - 214
• Main Authors: Papastamatiou, Yannis P., Lowe, Christopher G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2005
• Subjects: Animals; Data-loggers; Digestion; Eating - physiology; Elasmobranchii; Energetics; Fasting - physiology; Female; Foraging ecology; Gastric Acid - secretion; Gastric pH; Ginglymostoma cirratum; Hydrogen-Ion Concentration; Leopard sharks; Male; Marine; Nurse sharks; Sharks - physiology; Species Specificity; Stomach; Triakis semifasciata; Energetics; Stomach; Gastric pH; Data-loggers; Leopard sharks; Nurse sharks; Digestion; Foraging ecology
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpb.2005.05.041

Vertebrates differ in their regulation of gastric acid secretion during periods of fasting, yet it is unknown why these differences occur. Elasmobranch fishes are the earliest known vertebrates to develop an acid secreting stomach and as such may make a good comparative model for determining the causative factors behind these differences. We measured gastric pH and temperature continuously during periods of fasting in captive free-swimming nurse sharks ( Ginglymostoma cirratum) using autonomous pH/temperature data-loggers. All nurse sharks secreted strong gastric acids (minimum pH 0.4) after feeding; however, for most of the sharks, pH increased to 8.2–8.7, 2–3 days after feeding. Half of the sharks also exhibited periodic oscillations in pH when the stomach was empty that ranged from 1.1 to 8.7 (acid secretion ceased for 11.3 ± 4.3 h day − 1 ). This is in contrast to the gastric pH changes observed from leopard sharks ( Triakis semifasciata) in a previous study, where the stomach remains acidic during fasting. The leopard shark is a relatively active, more frequently feeding predator, and continuous acid secretion may increase digestive efficiency. In contrast, the nurse shark is less active and is thought to feed less frequently. Periodic cessation of acid secretion may be an energy conserving mechanism used by animals that feed infrequently and experience extended periods of fasting.