Tolerance of chronic hypercapnia by the European eel Anguilla anguilla
2003
SUMMARY European eels were exposed for 6 weeks to water CO 2 partial
pressures ( P CO 2 ) from ambient (approx. 0.8
mmHg), through 15±1 mmHg and 30±1 mmHg to 45±1 mmHg in
water with a total hardness of 240 mg l –1 as
CaCO 3 , pH 8.2, at 23±1°C. Arterial plasma
P CO 2 equilibrated at approximately 2 mmHg above
water P CO 2 in all groups, and plasma
bicarbonate accumulated up to 72 mmol l –1 in the group at a
water P CO 2 of 45 mmHg. This was associated with
an equimolar loss of plasma Cl – , which declined to 71 mmol
l –1 at the highest water P CO 2 .
Despite this, extracellular acid–base compensation was incomplete; all
hypercapnic groups tolerated chronic extracellular acidoses and reductions in
arterial blood O 2 content ( C a O 2 ), of
progressive severity with increasing P CO 2 . All
hypercapnic eels, however, regulated the intracellular pH of heart and white
muscle to the same levels as normocapnic animals. Hypercapnia had no effect on
such indicators of stress as plasma catecholamine or cortisol levels, plasma
osmolality or standard metabolic rate. Furthermore, although
C a O 2 was reduced by approximately 50% at the
highest P CO 2 , there was no effect of
hypercapnia on the eels9 tolerance of hypoxia, aerobic metabolic scope or
sustained swimming performance. The results indicate that, at the levels
tested, chronic hypercapnia was not a physiological stress for the eel, which
can tolerate extracellular acidosis and extremely low Cl –
levels while compensating tissue intracellular pH, and which can meet the
O 2 requirements of routine and active metabolism despite profound
hypoxaemia.
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