We studied the utilization of air versus water as a respiratory medium for O2 consumption (MO2) in the bimodally breathing African lungfish, Protopterus annectens (Owen, 1839), (151.2 ± 3.7 g) at 26-28°C. We also investigated the impact of a single meal on this respiratory allocation and nitrogenous waste excretion in lungfish entrained to a 48 h feeding cycle. Correction for the "microbial blank" was found to be critically important in assessing the aquatic component of MO2. After correction, total MO2 was low (∼1000 μmol· kg-1·h-1), and lungfish took about 40% of MO 2 from water and 60% from air. Following a meal of chironomid larvae (3.3% of body mass), MO2 values from both air and water increased in proportion over the first 3 h and continued to increase to a peak at 5-8 h postfeeding, at which point total MO2 (still 40% from water) was approximately 2.5-fold greater than the prefeeding level. When the same fish, entrained to the same 48 h feeding regime, were fasted, MO2 declined then later increased prior to the next anticipated feeding. In fed fish, the elevation in MO2 relative to fasted values was approximately 3-fold at 0-3 h and 9-fold at 5-8 h. This specific dynamic action (SDA) effect lasted until 23-26 h and amounted to only 9.5% of the oxycalorific content of the ingested meal. N-waste efflux was only slightly elevated after feeding, where there was a tendency for greater urea-N excretion (significant at 42-48 h); however, the lungfish remained ammoniotelic overall during the 48 h postfeeding period.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology