PAPASTAMATIOU, Yannis P.*; LOWE, Christopher G.; HOLLAND, Kim N.; University of Hawaii at Manoa; California State University Long Beach; University of Hawaii at Manoa: Variations in the response of gastric acid secretion during periods of fasting between shark species

Elasmobranchs are the earliest known vertebrates to have developed an acid secreting stomach and also exhibit a variety of foraging modes. Inter-specific differences in the response of acid secretion during periods of fasting are thought to exist amongst elasmobranches, although the causative factors behind these differences are unknown. We have measured gastric pH continuously, using autonomous pH data-loggers, in free sw!
imming leopard (Triakis semifasciata), nurse (Ginglymostoma cirratum), and blacktip reef sharks (Carcharhinus melanopterus) and found that leopard and blacktip reef sharks continuously secrete gastric acid, while nurse sharks periodically cease acid secretion while fasting. Measurements of acid secretion rates, pepsin levels and a mathematical model of gastric pH changes, suggest that maintaining a continuously acidic stomach may decrease digestion time of a subsequent meal by 5-7 hours in leopard sharks. We hypothesize that frequently feeding shark continuously secrete gastric acid as it provides antiseptic conditions, while reducing digestion time of a subsequent meal. Infrequently feeding sharks periodically shut down acid secretion as an energy conserving mechanisms while fasting.