The Metabolic Responses And Acid-base Status After Feeding, Exhaustive Exercise, And Both Feeding And Exhaustive Exercise In Juvenile 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 (EPOC) 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. At the same time, we investigated arterial blood acid–base status (pHa and [HCO3-]pl), oxygen consumption (VO2), ventilation frequency (Vf,), hemoglobin (Hb), blood glucose, blood lactate, muscle glycogen and muscle lactate concentrations after feeding, exhaustive exercise and both feeding and exhaustive exercise.The results as follows:1. In fasting fish, the pHa was 7.74±0.02. After feeding, the pHa showed no significant change within 3 h of feeding. However, pHa significantly increased by 0.14 units and reached a peak at 6 h after feeding (7.88±0.02). This transient increase slowly returned to the fasting pHa levels at 12—24 h after feeding.2. In fasting fish, the [HCO3-]pl was 5.42±0.29 mmol L-1. The increase in pHa was accompanied by a significant increase in [HCO3-]pl, which also peaked at 6 h (7.83±0.37 mmol L-1) after feeding and then slowly returned to fasting levels at 12 h.3. After feeding, the VO2 increased significantly, peaking at about 2.24 times higher than that of the pre-feeding level, and the increased metabolism persisted 52 h after ingestion. Feeding had no significant effect on Vf,, PCO2, [glucose]pl, [lactate]pl, Hb, white muscle lactate and white muscle glycogen.4. Exhaustive exercise led to a significant reduction in pHa by 0.46±0.06 units and a reduction in [HCO3-]pl by approximately 3 mmol L-1. After exhaustive exercise, the [lactate]pl significantly increased and peaked at 1 h. The pHa, [HCO3-]pl and [lactate]pl returned to resting levels at 4 h after exercise.5. The VO2 increased significantly after exhaustive exercise and gradually returned to pre-exercise level in fasting fish. The relationship between post-exercise VO2 (Y, mg O2 h-1kg-1) and time after exercise (X, min) was described by the following equation: Y=a±becx.6. The lactate concentration of white muscle rose acutely from a basal value of 4.80±0.26μmol g-1 to a peak level of 18.26±0.55μmol g-1 at 2 h after exercise in fasting fish and returned to pre-exercise level by 8 h. Exhaustive exercise caused a 61% decrease in glycogen, which remained low for at least 16 h post-exercise.7. In both feeding and exhaustive exercise fish, which had a higher pHa and [HCO3-]pl before exercise, exhaustive exercise only caused a reduction in pHa by 0.36±0.05 units and a reduction in [HCO3-]pl by about 2 mmol L-1.8. In both feeding and exhaustive exercise fish, the VO2 recovery profile was similar to those of fasting fish. However, there were significant differences in pre-exercise VO2, peak VO2 and the VO2 factorial scope between fasting and post-feeding fish. The EPOC between fasting and post-feeding fish was not significantly different.9. In both feeding and exhaustive exercise fish, the elimination of the lactate and the restoration of glycogen were similar to those of fasting fish.In conclusion:1. As anticipated, we detected a significant alkaline tide in Chinese catfish after feeding. To our knowledge, this is the first report of an alkaline tide in a teleost other than rainbow trout.2. Unlike other vertebrate classes, the alkaline tide in Chinese catfish may be compensated by excretion of metabolic base to the environment, so the PCO2 of the arterial blood did not change during digestion.3. The alkaline tide did dampen the reduction in pHa and [HCO3-]pl after exhaustive exercise, but recovery from the exhaustive exercise was not affected by digestion.