Belgium

Tuna associated with Fish Aggregating Devices (FADs) often exhibit higher proportions of empty stomachs and lower condition factors. However, it remains unclear whether this lower condition is a cause or a consequence of FAD association and whether the FAD-associated tuna condition is good or bad, due to the lack of fundamental knowledge on tuna physiology. This study aimed to quantify the physiological condition of tuna during food deprivation. 25 captive tuna individuals (FL: 31-71 cm) were initially fed ad libitum for 2 weeks and then subject to a controlled fasting period of 36 days. During fasting, 3 to 7 individuals were sampled at regular intervals (every 3-6 days) to assess various condition factors, including biometric parameters (e.g., Le Cren condition factor (Kₙ), hepatosomatic index (HSI), and girth length index (GL)), bioelectrical impedance analysis (BIA), body composition, and blood parameters. The results indicate that tuna initially mobilized the energy stored in the liver and then in the muscles. Three distinct phases of fasting were identified: Phase 1 (high HSI and Kₙ during ad libitum feeding and the early fasting days), Phase 2 (low HSI and high Kₙ, from days 4 to 14), and Phase 3 (low HSI and low Kₙ after 14 days of fasting). When comparing these results with condition factors measured on wild tuna associated with drifting FADs, it appears that all FAD-associated tuna fall within Phases 1 and 2. These results suggest that FAD-associated tuna do not attain the low Kn values observed during extended periods of fasting.

SEB Conference 2025

PHYSIOLOGICAL CONDITION OF YELLOWFIN TUNA CHARACTERIZED THROUGH A FASTING EXPERIMENT

refeeding

yellowfin tuna

physiological condition

fasting

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technical paper

Research on the direct effects of capture and tagging on post-release behaviour is typically limited to short-term deployments. To investigate both immediate and longer-term behavioural responses, we deployed eight Cefas G7 tags (1Hz depth and temperature, and 20 Hz triaxial acceleration) for 21 - 94 hours and MiniPATs (depth, temperature, light and triaxial acceleration, each at 0.2 Hz) for 110 - 366 days on Atlantic bluefin tuna (ABT) in the English Channel. Post-release, ABT exhibited a highly active initial swimming response, aligning with previous pelagic fish tracking studies. Accelerometry tags revealed that activity (VeDBA), tailbeat amplitude and dominant strokefrequency were 2.4, 3.2 and 1.4 times greater respectively in the first hour post-release than the subsequent 24 hours, stabilising at lower levels within 5 - 9 hours. Long-term MiniPATs data revealed reduced activity for 11 ± 7.9 days (range: 2-26 days), with disrupted diel patterns of activity and fewer burst energy events (5 min/day vs. 14 min/day during “recovery” periods). Subsequently, activity levels stabilised, with increased high-magnitude acceleration events (potential feeding) and became more active during the day than at night. Year-long deployments revealed that consistent diel vertical migration, diurnal patterns of activity, and increased time allocation to fast starts are typical for ABT off the British Isles in summer months, and their absence at the start of data collection may be related to the effect of capture and tagging, which may be longer lasting, and more complex than previously appreciated.

Use of accelerometry to measure the dynamics of activity patterns of Atlantic bluefin tuna after tagging and release

Any skeletal abnormalities arising in early life can have lifelong consequences for fish performance. Skeletogenesis is a tightly regulated process, highly sensitive to abiotic factors and environmental change. Fish must cope with increased temperatures and declining pH, as well as with pollutants released into the environment by human activities. Our study aims to determine how warming modulates stressor impacts on zebrafish skeletal development. Zebrafish larvae were exposed to warming (31.5°C), acidification (pH 4.5) and cadmium (0.3µM) from 0 till 7 days post fertilisation. Multiple lines of evidence show clear disruption of skeletogenesis following exposure to stressors (gene expression, staining, whole-body mineral content and swimming essays). Warming accelerates all physiological processes, including calcification, and was shown to partly attenuate the disruption due to acidification. This attenuating effect of warming was found even after accounting for thermal effects on development by comparing fish at the same developmental stage. In contrast, cadmium induced disruption was not attenuated by warming. Cadmium and acidification were found to affect the swimming behaviour of larvae during the night, dependent on environmental temperature. In summary, we found that multiple stressors impact calcium metabolism, bone development and swimming behaviour of zebrafish larvae. However, we did not observe strong amplification of stressor effects in a multi-stressor context.

Does warming amplify or attenuate the impacts of pollutants and low pH on zebrafish skeletal development? Evidence from gene expression, bone formation and swimming performance.

Exposure to environmentally generated stressors during early development can profoundly shape physiology and behaviour. To which extent such organisational effects might be contingent on subsequent environmental circumstances, maximise physiological resilience and fitness outcomes remain unclear. Using a highly seasonal study system, the migratory Common quail (Coturnix coturnix), we tested the prediction that exposure to food uncertainty potentiate the expression of seasonal migratory fattening and that such a response is stronger in those birds previously exposed to the same environmental stressor during early post-natal growth. To this end, we combined known proxies of physiological energetics signalling the emergence of the migratory phenotype (including fat stores and nocturnal energy expenditure) with circulatory measurements of metabolic hormones (plasma corticosterone and plasma thyroid hormones), and gene expression measurements of candidate genes in the brain. Our results suggest that the impact of stress exposure on the migratory phenotype is dependent on early-life priming effects, and potential functional mechanisms will be discussed.

The influence of early life environmental conditions on seasonal energy turnovers in the Common quail

All birds have a remarkably efficient balance. This is particularly evident in their ability to maintain an upright posture when resting or sleeping. Unlike humans lineage, the different parts of the pelvic apparatus are not aligned perpendicular to the ground, so they cannot be held upright by the compressive force of gravity.
Our previous work has shown, using robotic simulation, that birds with this flexed posture can passively maintain a bipedal position via a tensegrity system. We use our previous model and vary its geometric parameters according to four bird species (Zebra Finch, Mallard, Egret and Macaw) representing different leg proportions. We check the generalisation of our model by applying it to the four species. For each case, we determine the requirements to reach a stable equilibrium.
Based on our results, we propose a new model to simulate a wide range of avian pelvic limb proportions and determine the associated stability zone, i.e. the area in which the Centre of Mass (COM) can evolve while maintaining balance. The aim is to compare, describe and identify the parameters that allow the bipedal equilibrium to be maintained in a stable passive manner. We have also identified new features in the maintenance of postural balance, such as the bony and supra-tendinous bridges located on the distal part of the tibiotarsus. Our results provide a better understanding of how birds maintain a stable bipedal posture, as well as providing elements for the future development of bipedal robots.

Robotics contribution to the understanding of passive bipedalism in birds, balance and stability explained by tensegrity

How vertebrates that ingest their prey whole and dissolve the skeleton can process high amounts of calcium and phosphorus passing through the intestine? This was assessed using captive Burmese pythons facing different diets: a normal diet (calcium and phosphorus provided from entire rodents); a low-calcium and phosphorus diet (rodents with no bones: ‘boneless prey’), and a calcium-rich diet (boneless rodents supplemented with intraperitoneal injection of calcium carbonate, CaCO3). The intestinal mucosa was analysed using microscopy techniques (alizarin red S and peroxidase staining, EDX analyses). Blood calcium and hormone levels (parathyroid hormone, PTH and calcitonin) were also analysed from fasting pythons and snakes repeatedly fed with either a normal prey or a boneless rat. Results revealed the presence of specialised cells along the intestine involved in the production of calcium and phosphorus particles (fed snakes). A multi-layered particle made of calcium, phosphorus and iron-rich nucleation elements in the centre is usually observed in the apical crypt of these cells. In fasting snakes, crypts are empty. When snakes are fed with a boneless prey, the particles are not observed, although iron elements are located within the crypts. When fed with a boneless meal supplemented with calcium, large particles fill the crypts. When snakes are fed repeatedly with a low-calcium diet, blood calcium level drops but calcitonin and PTH levels increase. So far this cell type was found in some Boidae, a Colubrid and the Gila monster, these vertebrates eating their entire prey. Therefore, a broader and thorough evolutionary analysis is needed.

A new cell type in the gut of Vertebrates ?

Cardiovascular diseases and protein malnutrition are public health problems that require attention. In this context, understanding the effects of low-protein diets on the heart and the therapeutic potential of TUDCA is essential. C57Bl/6 mice were divided into four groups: control (C), control + TUDCA (CT), restricted (R) and restricted + TUDCA (RT). For 16 weeks, they received normal-protein or low-protein diets and, in the last 15 days, were treated with TUDCA (300 mg/kg) or PBS. Animals in group R had lower body weight and lower serum concentration of total proteins. However, we did not observe any change in relation to heart/body weight. Morphometric analysis revealed cardiomyocyte hypertrophy in group R, which was reduced by TUDCA in group RT. Similar results were observed in interstitial and perivascular collagen deposition. The TUNEL assay indicated the highest rate of cell death in group R, reduced in RT. Structural alterations in the sarcomere and in the organization of type 2 myosin were evident. The length of sarcomeres, myofibrils and A and I bands was shorter in the R group, but in the RT group these structures presented measurements similar to those of the control. In addition, R mice exhibited greater structural disorganization and an increase in the termination points between the myofibrils. Thus, the low-protein diet induces hypertrophy, collagen accumulation, apoptosis and sarcomeric alterations in the heart, while TUDCA exerts a therapeutic effect by reducing these alterations.
Keywords:Cardiomyocytes; myosin type 2; fibrosis, hypertrophy, myofibrils.

TUDCA attenuates structural changes in the hearts of mice fed a low-protein diet

The time when all taught content in higher education could be assessed with an essay or exam is long since passed. Good assessment practice currently requires authenticity in the assignment, robustness against AI and allowance for students to have some level of choice and autonomy. Meeting all of these criteria is a daunting and challenging task. Here I show how a few tweaks to assessment practice can help a move towards meeting some of these criteria, either by incorporating local businesses to improve authenticity, by moving away from written assessments to adopt a more AI robust framework using modified Vivas or by simply creating options for students to tailor their assessments to better meet their interests.

Quick wins in improving authenticity, robustness and choice in assessments

Silene nutans (Caryophyllaceae) is composed of 4 distinct genetic lineages which are strongly reproductively isolated: inter-lineage hybrids are chlorotic and exhibit high mortalities. The asymmetry in the reproductive isolation in reciprocal crosses suggested the involvement of cyto-nuclear incompatibilities in hybrid breakdown. Using hybrid capture and high-throughput DNA sequencing, we analyzed diversity patterns in the genic content of the organellar genomes in the four S. nutans lineages. Because organellar genomes are usually co-transmitted, we assessed whether both genomes could be involved in the speciation process.

What is the role of the organelles in the speciation process of Silene nutans?

Stomata arise during leaf epidermal development as specialised structures for gas-exchange. Stomatal numbers, apertures and distribution between leaf surfaces can affect plant water balance, growth and yield. While the mechanisms that govern the formation of stomata on the abaxial (lower) leaf surface are well-studied, how stomata develop on the adaxial (upper) leaf surface is poorly understood. How the distribution of stomata between leaf sides (stomatal ratio) is determined and adjusted in response to plant growth environment also remains unclear.
We addressed the effects of environmental conditions on adaxial and abaxial stomatal patterns in Arabidopsis thaliana. Acclimation to dry air or warm temperatures in Arabidopsis leaves manifests in substantial changes in stomatal density, small changes in stomatal ratio and minor, if any, changes in stomatal index. Thus, acclimation to growth environment may be mostly mediated by changes in cell expansion and less by alterations in leaf developmental program.
We also explored the relationships between stomatal anatomical traits and yield in crops. In spring wheat that has relatively more stomata on the adaxial leaf surface, higher adaxial but not abaxial stomatal density was negatively associated with yield, especially under dry and warm conditions. In tomato that has less stomata on the adaxial than abaxial leaf surface, higher stomatal ratios were positively associated with yield. Thus, manipulation of adaxial stomatal densities and stomatal ratios may increase yield in both monocot and dicot crops. Understanding how adaxial stomatal development is controlled and how stomatal ratios are regulated is necessary to achieve this goal.

Stomatal distribution between leaf surfaces and its relationships with yield

The climate crisis is increasing the likelihood of plant shoot failure due to mechanical overload, which is often presented as lodging. Currently up to 50% of UK oilseed rape yield can be lost when plant stems fail due to environmental conditions such as wind and rain. This crop failure rate will likely increase as extreme weather becomes more frequent, with disproportionate impact on the Global South. In this study, the model plant Arabidopsis thaliana, a relative of many common Brassicaceae crops, was used to understand stem remodelling in response to controlled magnitudes of wind load. Wind load inputs were quantified using hot wire anemometry. Plant remodelling outputs were measured using techniques such as uniaxial bending tests, histology and 3D laser scanning. We found that the force exerted by Arabidopsis stems during bending falls within a gap in the sensitivity range of commercially available uniaxial mechanical testing devices; thus, we designed and built a custom rig. The rig was designed to be open-source, affordable, user-friendly and easily manufacturable using 3D-printed parts. Using this, Arabidopsis stem bending tests were completed and methods developed to systematically link the mechanical inputs to plant remodelling outputs. Experimental data informs on failure loads/modes, plant strength and stability. The data will be built into computational models to understand internal stress and strain, to simulate environmental conditions that cannot be tested experimentally, and to predict remodelling response.

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Use of accelerometry to measure the dynamics of activity patterns of Atlantic bluefin tuna after tagging and release

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