The physiological consequences of a very large natural meal in a voracious marine fish, the staghorn sculpin (Leptocottus armatus).

Little information exists on physiological consequences when wild fish eat natural food. Staghorn sculpins at 10°-13°C voluntarily consumed 15.8% of their body weight in anchovies. Gastric clearance was slow with>60% of the meal retained in the stomach at 48h, and not complete until 84h. At 14-24h post-feeding, pH was depressed by 3 units and [Cl-] elevated 2-fold in gastric chyme, reflecting HCl secretion, while in all sections of the intestine, pH declined by 1 pH unit but [Cl-] remained unchanged. PCO2 and [total ammonia] were greatly elevated throughout the tract, whereas PNH3 and [HCO3-] were depressed. Intestinal HCO3- secretion rates, measured in gut sacs in vitro, were also lower in fed fish. Whole animal O2 consumption rate was elevated approximately 2-fold for 72h post-feeding, reflecting "specific dynamic action", whereas ammonia and urea-N excretion rates were elevated about 5-fold. Arterial blood exhibited a modest "alkaline tide" for about 48h, but there was negligible excretion of metabolic base to the external seawater. PaCO2 and PaO2 remained unchanged. Plasma [total amino acids] and [total lipids] were elevated about 1.5-fold for at least 48h, whereas small increases in plasma [total ammonia], PNH3, and [urea-N] were quickly attenuated. Plasma [glucose] remained unchanged. We conclude that despite the very large meal, slow processing with high efficiency minimizes internal physiological disturbances. This differs greatly from the picture provided by previous studies on aquacultured species using synthetic diets and/or force-feeding. Questions remain about the role of the gastro-intestinal microbiome in nitrogen and acid-base metabolism.