Control of breathing in African lungfish ( Protopterus dolloi ): A comparison of aquatic and cocooned (terrestrialized) animals

Abstract African lungfish, Protopterus dolloi exhibited constant rates of O2 consumption before (0.95 ± 0.07 mmol kg−1 h−1 ), during (1.21 ± 0.32 mmol kg−1 h−1 ) and after (1.14 ± 0.14 mmol kg−1 h−1 ) extended periods (1–2 months) of terrestrialization while cocooned. Although a breathing event in terrestrialized fish consisted of multiple bouts of inspiration and expiration in rapid succession, the mean frequency of pulmonary breathing events was unaltered in the terrestrialized fish (16.7 ± 1.4 h−1 versus 20.1 ± 4.9 h−1 in the aquatic and terrestrialized fish, respectively). Hypoxia (∼20 mmHg) increased the frequency of breathing events by 16 and 23 h−1 in the aquatic and terrestrialized fish, respectively. Hyperoxia (∼550 mmHg) decreased breathing event frequency by 10 and 15 h−1 in the aquatic and terrestrialized animals. Aquatic hypercapnia (∼37.5 mmHg) increased pulmonary breathing frequency (from 15.3 ± 2.3 to 28.7 ± 5.4 h−1 ) in free swimming lungfish, whereas aerial hypercapnia was without effect in aquatic or terrestrialized fish.