ABSTRACT

The African sharptooth catfish Clarias gariepinus has bimodal respiration, it has a suprabranchial air-breathing organ alongside substantial gills. We used automated bimodal respirometry to reveal that undisturbed juvenile catfish (N=29) breathed air continuously in normoxia, with a marked diurnal cycle. Air breathing and routine metabolic rate (RMR) increased in darkness when, in the wild, this nocturnal predator forages. Aquatic hypoxia (20% air saturation) greatly increased overall reliance on air breathing. We investigated whether two measures of risk taking to breathe air, namely absolute rates of aerial O₂ uptake (Ṁ_O2,air) and the percentage of RMR obtained from air (%Ṁ_O2,air), were influenced by individual standard metabolic rate (SMR) and boldness. In particular, whether any influence varied with resource availability (normoxia versus hypoxia) or relative fear of predation (day versus night). Individual SMR, derived from respirometry, had an overall positive influence on Ṁ_O2,air across all contexts but a positive influence on %Ṁ_O2,air only in hypoxia. Thus, a pervasive effect of SMR on air breathing became most acute in hypoxia, when individuals with higher O₂ demand took proportionally more risks. Boldness was estimated as time required to resume air breathing after a fearful stimulus in daylight normoxia (T_res). Although T_res had no overall influence on Ṁ_O2,air or %Ṁ_O2,air, there was a negative relationship between T_res and %Ṁ_O2,air in daylight, in normoxia and hypoxia. There were two T_res response groups, ‘bold’ phenotypes with T_res below 75 min (N=13) which, in daylight, breathed proportionally more air than ‘shy’ phenotypes with T_res above 115 min (N=16). Therefore, individual boldness influenced air breathing when fear of predation was high. Thus, individual energy demand and personality did not have parallel influences on the emergent tendency to take risks to obtain a resource; their influences varied in strength with context.