Effects of environmental hypercapnia on pulmonary ventilation of the South American lungfish

Abstract

Aquatic hypercapnia at PCO 2 of 55 mmHg significantly increased pulmonary ventilation in the South American lungfish Lepidosiren paradoxa, whereas no significant increases occurred when hypercapnia was applied to the gas phase with or without concomitant aquatic hypercapnia. On return from gas phase hypercapnia to inspiration of air there was a marked transient increase of ventilation. This post-hypercapnic response is discussed in relation to the possible presence of upper airway or pulmonary CO 2 receptors that inhibit pulmonary ventilation during hypercapnia. Post-hypercapnic hyperpnea has been reported for various groups of reptiles and for anuran amphibians. The occurrence of post-hypercapnic hyperpnea in Lepidosiren adds new information related to the evolution of respiratory regulation in vertebrates. 2001 The Fisheries Society of the British Isles

Relationship between cerebro‐spinal fluid pH and pulmonary ventilation of the South American lungfish, Lepidosiren paradoxa (Fitz.)

“…When water PCO 2 rose from 0 to 20 mmHg, this species increased respiratory frequency of pulmonary ventilation 2-fold from about 12 to 24 breaths/hr (Johansen and Lenfant,'68). Likewise, Lepidosiren increased pulmonary ventilation in response to higher water CO 2 levels (Sanchez and Glass, 2001), indicating a similar respiratory control in the two species.…”

“…Once again, this indicates that lungfish share various features of pulmonary ventilatory control with the tetrapods. Recently, Sanchez and Glass (2001) reported that Lepidosiren exhibits "post-hypercapnic hyperpnea." When combined with aquatic hypercapnia, inspiration of hypercapnic gases into the lungs slightly increased pulmonary ventilation.…”

“…Pulmonary ventilation was calculated as tidal volume times the respiratory frequency per hour. For an example of recordings by the above method, see Sanchez and Glass (2001).…”

Air‐breathing fishes in aquaculture. What can we learn from physiology?

“…In tropical aquaculture ponds with high stocking density, no aeration and little water exchange, CO 2 is likely to reach high levels because air-breathing fishes typically obtain oxygen from the air breathing organ, but excrete CO 2 across their gills into the water (Evans et al, 2005;De Lima Boijink et al, 2010). One exception may be L. paradoxa which appears to increase lung rather than gill ventilation during exposure to hypercapnia (Sanchez & Glass, 2001). In many tropical areas, water is rather poorly buffered and the putatively high CO 2 level would therefore cause considerable reductions in water pH.…”

Sensing and transfer of respiratory gases at the fish gill

“…It has long been recognised that fish exhibit pronounced physiological responses, including hyperventilation and catecholamine release, when exposed to environmental hypercarbia (see review by Perry and Wood,'89); more recently, the cardiovascular responses to hypercarbia have been characterised. Species from several major groups have been studied including representatives from the Chondrichthyes (Randall et al,'76;Heisler et al,'88;Graham et al,'90), Chondrostei (Crocker et al, 2000), Lepisosteidae (Smatresk and Cameron,'82), Dipnoi (Sanchez and Glass, 2001), and Teleostei (Janssen and Randall, '75;Burleson and Smatresk, 2000;Reid et al, 2000;Soncini and Glass, 2000;Sundin et al, 2000;Perry and McKendry, 2001). Until recently, it was generally accepted that the physiological responses to hypercarbia were not directly attributable to changes in CO 2 /pH but instead were an indirect effect of the marked Bohr and Root effects that occur during hypercapnic acidosis.…”