The influence of feeding on aerial and aquatic oxygen consumption, nitrogenous waste excretion, and metabolic fuel usage in the African lungfish, Protopterus annectens

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 Mo2 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.