Experimental Biology Online - EBO 

ISSN 1430-3418 

The Society for Experimental Biology
Annual Meeting

University of Kent at Canterbury
7-11 April 1997

General Respiration [A13]

Respiratory and cardiovascular adaptations in the South American lungfish – a paradox revisited [A13.4 ]

V.Harder¹, R.H.S. Souza², W. Severi³, F.T. Rantin⁴ and C.R. Bridges¹

² Physiology, CEPTA Pirassununga

³ Ecology, University of Mato Grosso

⁴ Physiology, Federal University of Sao Carlos

Among three recent genera of lungfishes, a group that according to Lenfant et al. (1967) "provides a unique opportunity to study the physiological adaptations correlated with the emergence of airbreathing", the South American lungfish Lepidosiren paradoxa is structurally the most advanced and shows the greatest degree of atrial subdivision and ventricular septation. In contrast, however, to its African counterpart Protopterus, the South American lungfish is only poorly represented in physiology literature.

The obligate airbreather Lepidosiren inhabits rivers and lakes both in tropical (Amazon) and subtropical (Pantanal) regions. It has been suggested that this species aestivates up to several months in moist mud burrows during the dry season.

In the present study heart rate, cardiac output and breathing frequency of active and, for the first time, burrowed individuals have been investigated. In addition oxygen uptake and carbon dioxide excretion were determined and, in order to characterize environmental conditions, physico-chemical parameters have been monitored in the natural habitat over a 3-month period by means of water analysis. Burrowed individuals show a dramatic increase in the airbreathing frequency (sevenfold), while the heart rate remains – with the exception of during the first hours in the mud, when a bradycardia occurs – unaffected. Lepidosiren does not show a similar change in the airbreathing rate when submitted to graded hypoxia. Under hypoxic conditions the gill ventilation is significantly (P<0.05) reduced compared to normoxic values.

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