Investigating real-time arterial oxygen tensions in fish

Collaboration: Deakin University & University of Gothenburg

Oxygen uptake across the gills has been proposed as a potential bottleneck in the oxygen transport cascade of aquatic animals. However, most studies to date have relied on intermittent blood sampling for assessment of blood oxygen status, offering only brief snapshots of arterial blood oxygenation. This limitation has left significant gaps in our understanding of gill oxygen uptake in fish, particularly under rapidly changing environmental conditions.

To address this, we implanted ‘oxygen miniprobes’ directly into the dorsal aorta of rainbow trout (Oncorhynchus mykiss, n=25; Fig. 1). This allowed for continuous, real-time monitoring of arterial oxygen tension (PaO₂), offering unprecedented resolution in tracking how gill oxygen uptake responds to varying metabolic demands.

We applied this approach under three acute experimental challenges: thermal stress, exhaustive exercise, and progressive hypoxia. These pilot trials served to explore the potential for generating new physiological insights. Furthermore, in a subset of fish, we also collected conventional arterial blood samples in order to validate probe readings.

Fig. 1: Conceptual figure of an implanted oxygen miniprobe inserted into the dorsal aorta of rainbow trout (Oncorhynchus mykiss), allowing for the investigation of gill oxygen uptake

Our study results were highly promising. Starting from the surgical implantation where PaO₂ readings responded dynamically to the flow of ventilatory water across the gills. Intermittently removing gill irrigation (perfusion) or alternating between one-sided and two-sided gill perfusion caused marked changes in PaO2 (Fig. 2), confirming the system’s sensitivity. The signal persisted for more than 48 h after the implantation (the maximum length of the experimental protocol), and on-line PaO₂ measurements were consistent with values obtained from blood samples. The real-time recordings revealed some intriguing patterns of gill oxygen uptake that we look forward to presenting in more detail in future publications.

Our findings demonstrate the feasibility and accuracy of continuous PaO₂ monitoring in fish using dorsal aortic oxygen sensors. On-line PaO₂ readings were highly responsive, consistent with blood samples, and revealed dynamic oxygenation patterns during thermal, exercise, and hypoxic stress. This approach opens up exciting new opportunities to explore the fine-scale dynamics of gill oxygen uptake in response to aerobic challenges. In particular, it holds strong potential for empirically addressing long-standing questions about the role of gill oxygen limitation in fish.