Belgium

Oxygen uptake across the gills has been proposed as a bottleneck in the oxygen transport cascade of pelagic fish with high aerobic requirements. However, most investigations of this topic have relied on intermittent blood sampling, which only provides a snapshot in time of blood oxygenation, so large knowledge gaps remain.
We present a novel method with exciting potential for the study of oxygen uptake limitation in fish. By implanting oxygen sensors into the dorsal aorta of the highly athletic rainbow trout (Oncorhynchus mykiss, n=25), arterial oxygen tension (PaO₂) immediately downstream of the gills could be monitored continuously. We combined this with whole animal respirometry at two distinct water flow regimes within the respirometers (10 and 20 l min⁻¹) and hypothesised that increased flow rates would enhance arterial oxygenation and maximum metabolic rate (MMR) following exhaustive exercise at 20°C. The Pao2  recordings were validated by assessments of dorsal aortic PaO2  and O2  content from intermittent blood samples collected from a separate group of fish.
Intriguingly, PaO₂ closely tracked the minor water oxygen deviations associated with flush and seal cycles during respirometry. Pilot tests exposing the fish to &lt;20% water oxygen saturation confirmed that fish only loosely defend their PaO₂ via hyperventilation and other measures. High water flow did not significantly affect MMR or PaO₂ recovery times, suggesting gill oxygen uptake was not limited following exercise. We highlight research avenues that our new approach has uncovered and discuss how remaining knowledge gaps surrounding gill oxygen uptake dynamics of fish can be addressed.

SEB Conference 2025

On-line arterial oxygen tensions provide insight into gill oxygen uptake dynamics in rainbow trout

arterial oxygen tension

gill oxygen uptake; rainbow trout

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SEB Conference 2024

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Oxygen uptake across the gills has been proposed as a bottleneck in the oxygen transport cascade of pelagic fish with high aerobic requirements. However, most investigations of this topic have relied on intermittent blood sampling, which only provides a snapshot in time of blood oxygenation, so large knowledge gaps remain.
We present a novel method with exciting potential for the study of oxygen uptake limitation in fish. By implanting oxygen sensors into the dorsal aorta of the highly athletic rainbow trout (Oncorhynchus mykiss, n=25), arterial oxygen tension (PaO₂) immediately downstream of the gills could be monitored continuously. We combined this with whole animal respirometry at two distinct water flow regimes within the respirometers (10 and 20 l min⁻¹) and hypothesised that increased flow rates would enhance arterial oxygenation and maximum metabolic rate (MMR) following exhaustive exercise at 20°C. The Pao2  recordings were validated by assessments of dorsal aortic PaO2  and O2  content from intermittent blood samples collected from a separate group of fish.
Intriguingly, PaO₂ closely tracked the minor water oxygen deviations associated with flush and seal cycles during respirometry. Pilot tests exposing the fish to <20% water oxygen saturation confirmed that fish only loosely defend their PaO₂ via hyperventilation and other measures. High water flow did not significantly affect MMR or PaO₂ recovery times, suggesting gill oxygen uptake was not limited following exercise. We highlight research avenues that our new approach has uncovered and discuss how remaining knowledge gaps surrounding gill oxygen uptake dynamics of fish can be addressed.

technical paper

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Marine pelagic fishes present challenges for metabolic study. Many pelagic fish species are difficult to maintain in aquarium and respirometry conditions due to their requirements for large water volumes, sensitivity to handling and often schooling social behaviour. Consequently, basic physiological data on marine pelagic fishes is relatively sparse, and such data that does exist may reflect unrealistic and/or stressful conditions. Recently the development of stable isotope-based proxies for total oxygen consumption rate offers a possibility of obtaining metabolic rate estimates retrospectively from free swimming pelagic fishes at relatively low cost. In this presentation I will: (a) outline the physiological mechanism underpinning the otolith isotope metabolic rate proxy, (b) compare metabolic rate data obtained from otolith, oxygen uptake rate and electron transfer system respirometry approaches as applied to pelagic fishes ranging from deep pelagic bristlemouths to bluefin tuna.  Finally, I will demonstrate the use of otolith-derived metabolic data to identify optimal thermal habitat and thermal sensitivity of large pelagic fishes, and to quantify the contribution of deep pelagic fishes to global carbon export flux.

Otolith respirometry in pelagic fishes: Calibration and ecophysiological insights

Extreme heat events are predicted to be more frequent and intense over the next few decades. Ectotherm early stages are particularly sensitive to such events due to their reliance on the external environment to perform their daily activities and maintain body temperature. Exposure to higher temperatures during fish development can increase mortality, growth rates, and may impact adult phenotypes. Yet very little is known about the early-life responses, interactions and developmental plasticity to thermal stress in aquatic species. In this study, we measured the photomotor response (PMR) of 1 day post fertilization zebrafish embryos at different rearing densities (10, 20, and 40 eggs), with and without regular social and heat-induced chemical cues. We found that embryos exposed to stress metabolites showed significant changes in PMR magnitude and recovery time, indicating they may detect and respond to stress-related chemical cues. Higher rearing densities were associated with lower activity, and the combined effects of thermal stress and stress metabolites resulted in a unique behavioral phenotype, suggesting interactions that may amplify the stress responses. Thus, we showed that zebrafish embryo activity is significantly affected by early life exposure to higher temperatures and that social cues may create a buffer when not directly exposed to thermal stress. Since the photomotor response can be a proxy for how well sensory information and motor actions are coordinated, rearing density and social cues emerge as important factors for understanding the response of developing fish to environmental stressors.

Sensing stress: Chemical communication in thermally stressed zebrafish embryos 

The pseudobranch is an enigmatic organ in fishes with a still elusive function .[PF1]  It has its origin as gill tissue and has retained similarities in structure; however, in a number of species it has evolved as an embedded structure within the wall of the buccal-opercular cavity without a free surface exposed to the water, and thus lacking typical branchial roles in gas, ion and acid-base exchange with the environment. Since it represents a portal system with oxygenated blood continuing to the retina of the eye, it has thus been proposed to have a role in acidifying blood to aid oxygen unloading at the eye. We have evidence in other fishes that the sodium-proton exchanger-5 (nhe5/slc9a5) may be important in this blood acidification mechanism. To test this hypothesis, our objective was to compare the pseudobranch and Nhe5 expression in the eyed-surface and eyeless Chica cavemorphs of the Mexican tetra (Astyanax mexicanus). We predicted a reduced pseudobranch and reduction/absence of Nhe5 expression in the cavemorph. We found blood facing Nhe5 expression in the pseudobranch of the surface morph, and noted the apparent absence of this organ in the adult cavemorph. However, the organ could be detected histologically and although much reduced in size still expressed Nhe5. This was also reflected during larval development where the pseudobranch could be more easily detected than in the cavemorph. Taken together, our results indicate that the pseudobranch’s function is likely linked to the eye although not completely lost inA. mexicanusChicacavemorphs.

The fish pseudobranch: Na+/H+ exchanger 5's  role in blood acidification for eye oxygenation. Now you see it, now you don't?

When selective pressures for different functions act simultaneously on a structure, morphological diversification can be shaped by adaptation toward distinct functional optima. Systems may evolve along a performance gradient, optimizing different aspects of function in response to ecological demands.
We investigated two scorpion species representing the morphological extremes of chela (pincer) shape. Scorpion chelae exhibit remarkable morphological diversity associated with ecological roles, and their performance varies along a force-velocity continuum. To explore how structural and muscular adaptations shape performance, we developed a biomechanical model integrating synchrotron microtomography, muscle architecture, and performance data.
Our findings reveal that these species exhibit distinct structural and muscular arrangements, each optimized for a different performance outcome. The short-fingered species maximize closing force through increased mechanical advantage and longer sarcomeres, enhancing muscle contraction efficiency. In contrast, the slender-chela species optimizes closing velocity through muscle orientations that favor rapid acceleration. While additional functional demands likely influence these designs, one morphology appears specialized for quickly capturing prey, while the other seems to be adapted for prey crushing. These divergent performance optima may have played a key role in shaping the trophic ecology of scorpions and influencing the evolution of their venom.

Crushers and graspers: diversification of a musculoskeletal system toward two opposite functional optim

The rapid warming of the Arctic regions may have serious impact on cold-acclimated Arctic species. Polar cod (Boreogadus saida) is a key species in the Arctic food web, with a high biomass and an important prey item for larger fish, seabirds and marine mammals. Although the effect of warming on reproduction is crucial in assessing the vulnerability of a species to climate change, little is known about the impact of warming on the reproduction cycle of polar cod.
To study the influence of elevated temperatures on gonadal growth, female B. saida were incubated for six months at a control temperature of 0°C and at elevated temperatures of 3°C and 6°C from August 2022 to February 2023. Magnetic resonance imaging (MRI) to follow the gonad development was applied on a subsample of female individuals from October 2022 to January 2023. Gonadal volume and oocyte diameter were determined from MR images. Histological samples of gonads were taken to determine maturation stages at three sampling points (December, January and February) covering the spawning season. Initial results show that elevated temperature leads to a delay in gonad maturation. Fish at control temperatures reached maximum gonadal volume and most mature gonads in December, whereas females at 3°C showed continued development and females at 6°C showed only small gonads and did not reach the spawning capable stage during the experimental period. Our results indicate a trade-off between reproductive investment and maintenance costs at higher temperatures.

Effect of elevated temperature on gonadal maturation in female polar cod (Boreogadus saida)

The mineral pattern in the skull forms intricate, dynamic, lace-like designs as osteoblasts spread across the head. These patterns emerge from fine-scale dynamics, but uncovering the underlying mechanisms is challenging without tools to quantify such complexity. To address this, we developed multifractal methods to measure self-similarity in these patterns. Using these tools, we constructed toy models suggesting that a collagen gradient alone is sufficient to generate the multifractal patterns of developing bone. Through live imaging, physical perturbations, and additional mathematical modeling, we confirmed that this collagen gradient arises from a self-propagating differentiation wave. More broadly, our mathematical framework for pattern quantification provides a generalizable approach for studying cross-scale interactions that drive spatial pattern formation, offering new ways to explore the fundamental mechanisms underlying spatiotemporal dynamics in living systems.

Ossification across scales guides emergent multifractal biomineral pattern in the skull

Higher education was born in discussion classrooms, but also in dissection rooms and “physic gardens” (today botanic gardens). At their roots, biological higher education and experimental biology were very tightly intertwined.
These links may be experiencing greater challenges than they have for a long time, owing to their labour intensity and increasing financial constraints. Maintaining them, however, may be more important than ever given a widely-experienced reduced level of engagement of students in in-person lectures since the Covid pandemic.
Plants lend themselves very well to laboratory practicals, in plant science but also in cell biology, genetics and other disciplines. A current undergraduate module, “Green Planet”, compulsory for year 1 Biology students at our university, is using laboratory practicals developed and perfected over a number of years. They are focused on (1) flower evolution, using also floral homeotic mutants, (2) plant regeneration and hormone biology and (3) flowering time control, including the assessment and molecular genotyping (as problem-solving) of distinct photoreceptor mutants. The module also includes a photosynthetic CO2  capture demonstration, and a guided trip to the World-heritage Kew Gardens focusing on subjects of several lectures. Student participation in practicals approaches 100%, well above the lectures, and feedback is highly positive.
A practical in an advanced cell biology module involves inter-organellar communication, using chloroplast-nucleus interaction as a study case, with similarly positive outcomes.
Engaging practicals have hardly ever been of greater value in biological education than they are today.
Labs can be found in this higher education-focused repository:https://www.sebiology.org/outreach/biology-practicals-for-higher-education.html

Practicals make undergraduate plant science interesting, even fun

The Higher Education (HE) sector is undergoing a period of significant and rapid change as we grapple to respond to the post-pandemic landscape, political and economic uncertainty and significant technological developments. HE staff are facing increasing pressure to do more with less; to innovate and be exceptional and meet the needs of a rapidly changing student cohort. Teaching practices that may have been effective as little as 5 or 6 years ago, no longer necessarily reflect best practice. Finding the time and headspace to reflect on our practice, to innovate, adapt and evolve our pedagogical ideas is a sector-wide challenge. And the constant pursuit of teaching excellence is impacting the experiences of both staff and students. We are living to the words of Alice in Wonderland’s Red Queen “It takes all the running you can do to keep in the same place”
In this session, I will share examples of some of the strategies that I have developed within my own practice to enhance the student experience. The strategies are all grounded in relational pedagogy and include evaluating practical skills competency at the start of a course as well as changes to assessments and multiple ‘quick wins’ embedded within teaching that also serve to support student wellbeing. The strategies that I will share can be used by anyone teaching within HE across any level of study.

Quick wins to enhance the student experience

Stomatal regulation balances water use and carbon assimilation, directly influencing plant resilience under drought. Investigating natural variation in stomatal responses provides insights into how plants fine-tune water use strategies. This study examines the growth responses, potential trade-offs, and the influence of climate origin on trait variation under drought in 53 Arabidopsis ecotypes from diverse geographical origins. Plant projected area, chlorophyll fluorescence, and rosette temperature (stomatal regulation proxy) were monitored over time, revealing ecotypic variation in stomatal regulation and growth maintenance under drought. While all ecotypes employed a conservative strategy under drought, closing stomata to conserve water and reducing photosynthetic efficiency, they varied in the timing and intensity of their responses. A trade-off in stomatal conductance (gs) was observed in 42% of ecotypes, with those exhibiting higher gs under well-watered conditions experiencing a greater reduction under drought, indicating increased sensitivity to drought. Limited water availability led to a stronger trade-off between vegetative and reproductive growth, whereas in well-watered, sufficient resources allowed both to develop freely. Rather than distinct strategies, NMDS analysis revealed that drought responses followed a continuum of water-use strategies, ranging from risky-fast to safety-slow. Environmental origin played key roles in shaping drought responses, as ecotypes from regions with wider temperature ranges (p < 0.05) were more likely to adopt a safety-slow strategy, whereas warmer winter ecotypes (p < 0.05), mediterranean, tended toward a risky-fast approach. These findings highlight the diversification of stomatal and growth strategies within a single species, providing insights into how plants optimize water use under stress.

Drought-Induced Trade-Offs: Stomatal Closure, Growth, and Water Use in Arabidopsis Ecotypes

Improving the efficiency of converting light energy into organic biomass has been identified as a key factor required to increase crop yield. Classical kinetic models of photosynthesis have helped identify rate limiting steps of photosynthesis and have helped engineering efforts on this front. However, kinetic models are computationally expensive and depend on detailed information about kinetic laws, metabolite, and enzyme concentrations, which limits their scope. In contrast, constraint-based models of leaf metabolism are less data-reliant and can account for the entire leaf metabolism, making them a promising alternative for studying steady-state leaf metabolism. In my talk I will describe how constraint-based modeling works and how such models can be used to study metabolism in C3 and CAM leaves. I will also discuss our recent efforts in using this modeling approach to search for potential strategies to increase efficiency of tomato leaf metabolism. Our analysis revealed that a switch in the activity of glutamine synthetase (GS) from the chloroplast to the mitochondria could help a leaf achieve higher productivity. To further explore this prediction, transgenic tomato plants over-expressing GS in leaf mitochondria were generated. These plants exhibited faster growth rate and increased fruit yield. Leaf metabolomic profiling and enzyme activity analysis also showed GS activity in mitochondria played a role in enhancing the synthesis and export of sugar from the leaves. These findings increase our confidence in the use of constraint-based modeling as a viable approach for designing engineering strategies aimed at improving crop productivity.

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Otolith respirometry in pelagic fishes: Calibration and ecophysiological insights

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