Hypercapnia adversely affects postprandial metabolism in the European eel (Anguilla anguilla)

Abstract

The present study examined the effects of elevated CO2 partial pressure on the specific dynamic action (SDA) and ammonia excretion in European eel (Anguilla anguilla) following forced feeding. Two different hypercapnic scenarios were investigated; one in which pCO2 oscillated between 20 and 60mmHg over 24hourcycles, and one in which pCO2 was constant at 60mmHg. Since high CO2 results in low pH with unchanged alkalinity, a normocapnic group at low pH (pCO2≈3mmHg, pH=6.5) was included to investigate possible direct effects of pH. Constant hypercapnia (60mmHg) and low pH (pH=6.5) both significantly increased the duration of the SDA response by 22% and 29%, respectively. Hypercapnia had no effect on standard metabolic rate, while constant or oscillating hypercapnia significantly lowered the maximum metabolic rate compared to controls, causing a significant reduction of the aerobic scope during constant hypercapnia. Under conditions of oscillating pCO2, the temporal and spatial postprandial increase in ammonia nitrogen excretion was significantly reduced. This group also excreted significantly less ammonia after ingesting a meal. No significant effects on the magnitude or duration of postprandial ammonia excretion were observed at high pCO2 or low pH/normocapnia. The results demonstrate that despite an exceptional tolerance towards elevated pCO2 and acidosis, postprandial metabolic processes of the European eel are adversely affected by hypercapnia and low pH.