Synbranchus marmoratus (Bloch) breathes air during terrestrial excursions and while dwelling in hypoxic water and utilizes its gills and adjacent buccopharyngeal epithelium as an air-breathing organ (ABO). This fish uses gills and skin for aquatic respiration in normoxic (air-saturated) water but when exposed to progressive aquatic hypoxia it becomes a metabolic O2 conformer until facultative air breathing is initiated. The threshold PwOO2 (aquatic O2 tension or partial pressure in mmHg) that elicits air breathing in S. marmoratus is higher in larger fish. However, neither air-breathing threshold nor the blood haemoglobin (Hb) concentration of this species were changed following hypoxia (PwOO2 < 20 mmHg) acclimation. In hypoxic water S. marmoratus supplies all of its metabolic O2 requirement through air breathing. ABO volume scales with body weight raised to the power of 0.737 and the amount of O2 that is removed from each air breath depends upon the length of time it is held in the ABO. Ambient PwOO2 directly affects the air-breath duration of this fish, but the effect is smaller than in other species. Also, average air-breath duration (15.7 min at PwOO2 0–20 mmHg) and the average inter-air-breath interval (15.1 min) of S. marmoratus are both longer than those of other air-breathing fishes. Although the gills of S. marmoratus are involved in aerial O2 uptake, expelled air-breath CO2 levels are not high and always closely correspond to ambient PwCOCO2, indicating that virtually no respiratory CO2 is released to air by this fish. CO2 extrusion therefore must occur aquatically either continuously across another exchange surface or intermittently across the gills during intervals between air breaths. This study with S. marmoratus from Panama reveals physiological differences between this population and populations in South America. The greater Hb content of South American S. marmoratus may be the result of different environmental selection pressures.
In the field: an interview with Harald Wolf
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In our new Conversation, Harald Wolf talks about his fieldwork experiences working with desert ants in Tunisia to understand their navigation.
Propose a new Workshop
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Our Workshops bring together leading experts and early-career researchers from a range of scientific backgrounds. Applications are now open to propose Workshops for 2024, one of which will be held in a Global South country.
Julian Dow steps down and John Terblanche joins the JEB team
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After 15 years with the journal, Julian Dow from University of Glasgow, UK, is stepping down as a Monitoring Editor. We wish Julian all the best for the future and welcome John Terblanche, Stellenbosch University, South Africa, who is joining the team. Julian talks about his long association with The Company of Biologists and the journal and John tells us about his life and career in this News article.
Ecotourism affecting iguana glucose tolerance
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Ecotourists feeding grapes on skewers to north Bahamian rock iguanas may be doing the reptiles more harm than good as the sugar charged diet is giving the animals high blood sugar.
Evolution of metabolic plasticity
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In their Commentary, Frank Seebacher and Julian Beaman propose that metabolic plasticity originated in prebiotic protocells and that it was a pre-requisite for effective transfer of genetic material across generations – the hallmark of Darwinian evolution.
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