The metabolic responses and acid–base status after feeding, exhaustive exercise, and both feeding and exhaustive exercise in Chinese catfish (Silurus asotus Linnaeus)
Feeding and exhaustive exercise are known to elevate metabolism. However, acid–base status may be oppositely affected by the two processes. In this study, we first investigated the acid–base response of Chinese catfish to feeding (the meal size was about 8% of body mass) to test whether an alkaline tide (a metabolic alkalosis created by gastric HCl secretion after feeding) would occur. We then determined the combined effects of feeding and exhaustive exercise on excess post-exercise oxygen consumption and acid–base status to determine whether the alkaline tide induced by feeding protects against acid–base disturbance during exhaustive exercise and affects subsequent recovery. Arterial blood pH increased from 7.74 ± 0.02 before feeding to 7.88 ± 0.02 and plasma [HCO3−]pl increased from 5.42 ± 0.29 to 7.83 ± 0.37 mmol L−1 6 h after feeding, while feeding had no significant effect on $$ P_{{{\text{CO}}_{2} }} $$. Exhaustive exercise led to a significant reduction in pH by 0.46 units and a reduction of [HCO3−]pl by ~3 mmol L−1. Lactate concentrations in white muscle and plasma increased by 2.4 mmol L−1 and 13.4 μmol g−1, respectively. Fed fish had a higher pH and [HCO3−]pl than fasting fish at rest, and the reductions in pH (0.36 units) and [HCO3−]pl (~2 mmol L−1) were thus lower after exhaustive exercise. However, the recovery of acid–base status and metabolites were similar in digesting and fasting fish. Overall, a significant alkaline tide was found in Chinese catfish after feeding. The alkaline tide elicited by feeding significantly prevented the decreases in pH and [HCO3−]pl immediately after exhaustive exercise, but recovery from exhaustive exercise was not affected by digestion.