Unimodal head-width distribution of the European eel (Anguilla anguilla L.) from the Zeeschelde does not support disruptive selection

Since the early 20th century, European eels (Anguilla anguilla L.) have been dichotomously classified into 'narrow' and 'broad' heads. These morphs are mainly considered the result of a differential food choice, with narrow heads feeding primarily on small/soft prey and broad heads on large/hard prey. Yet, such a classification implies that head-width variation follows a bimodal distribution, leading to the assumption of disruptive selection. We investigated the head morphology of 272 eels, caught over three consecutive years (2015-2017) at a single location in the Zeeschelde (Belgium). Based on our results, BIC favored a unimodal distribution, while AIC provided equal support for a unimodal and a bimodal distribution. Notably, visualization of the distributions revealed a strong overlap between the two normal distributions under the bimodal model, likely explaining the ambiguity under AIC. Consequently, it is more likely that head-width variation followed a unimodal distribution, indicating there are no disruptive selection pressures for bimodality in the Zeeschelde. As such, eels could not be divided in two distinct head-width groups. Instead, their head widths showed a continuum of narrow to broad with a normal distribution. This pattern was consistent across all maturation stages studied here

Effects of land use and water quality on greenhouse gas emissions from an urban river system

Rivers act as a natural source of greenhouse gases (GHGs) that can be released from the metabolisms of aquatic organisms. Anthropogenic activities can largely alter the chemical composition and microbial communities of rivers, consequently affecting their GHG emissions. To investigate these impacts, we assessed the emissions of CO2, CH4, and N2O from Cuenca urban river system (Ecuador). High variation of the emissions was found among river tributaries that mainly depended on water quality and neighboring landscapes. By using Prati and Oregon Indexes, a clear pattern was observed between water quality and GHG emissions in which the more polluted the sites were, the higher were their emissions. When river water quality deteriorated from acceptable to very heavily polluted, their global warming potential (GWP) increased by ten times. Compared to the average estimated emissions from global streams, rivers with polluted water released almost double the estimated GWP while the proportion increased to ten times for very heavily polluted rivers. Conversely, the GWP of good-water-quality rivers was half of the estimated GWP. Furthermore, surrounding land-use types, i.e. urban, roads, and agriculture, significantly affected the river emissions. The GWP of the sites close to urban areas was four time higher than the GWP of the nature sites while this proportion for the sites close to roads or agricultural areas was triple and double, respectively. Lastly, by applying random forests, we identified dissolved oxygen, ammonium, and flow characteristics as the main important factors to the emissions. Conversely, low impact of organic matter and nitrate concentration suggested a higher role of nitrification than denitrification in producing N2O. These results highlighted the impacts of land-use types on the river emissions via water contamination by sewage discharges and surface runoff. Hence, to estimate of the emissions from global streams, both their quantity and water quality should be included

European silver eel (Anguilla anguilla L.) migration behaviour in a highly regulated shipping canal

Among the many man-made structures that facilitate shipping, navigable canals take an important position. These canals may offer energetically favourable migration routes for diadromous fish, but they may also obstruct fish migration, for instance at shipping locks. Because the use of shipping canals by, and their effects on, migrating fish remain unknown, we assessed whether these canals can play a significant role in the migration of the critically endangered European eel. Only one third of 70 acoustically tagged silver eels completed migration through a shipping canal, and did so at a very low pace (average < 0.06 m s(-1)) due to delays at shipping locks and most likely also due to the disruption of water flow. These delays may come at an energetic cost, hampering the chances of successful migration. Knowledge on the impact of shipping canals on diadromous fish is crucial for proper management regulations. For instance, the observation that eels mostly migrated at night and during spring and autumn can support water managers to define adequate measures to improve eel migration in shipping canals

European silver eel (Anguilla anguilla L.) migration behaviour in a highly regulated shipping canal

Over the last 40 years, Anguilla species in the northern hemisphere have shown a strong decline in recruitment. Due to a 98% recruitment decline, the European eel is now classified as critically endangered according to the IUCN Red List. To aid conservation and recovery of European eel populations, the European Union recently adopted a Council Regulation which imposes a management system that ensures 40% escapement of the spawning stock biomass, defined as the best estimate of the theoretical escapement rate if the stock were completely free of anthropogenic influences. Various causes likely contribute to the eel decline (e.g. pollution, human-introduced parasites, changes in ocean climate, habitat deterioration…), but habitat fragmentation by migration barriers that prevent the movement of silver eels between freshwater and the sea is probably one of the most important bottlenecks. During the last decades, a substantial number of canals has been developed, creating new habitat for eels. However, eel migration and potential obstacles in these systems are still underexplored. In this study, we tracked 131 European eels (Anguilla anguilla L.) from October 2014 till March 2017 in the Belgian Albert Canal with acoustic telemetry. The 130-km long canal is on average 86 m wide, 5 m deep and functions as a shipping route between the rivers Schelde and Meuse. The canal has a highly regulated water flow and six shipping locks to overcome the 56-m fall, which may have a negative impact on silver eel escapement. Indeed, we found significant delays (i.e. periods with a significantly prolonged residence time) and a ca 50% lower swimming speed near shipping locks compared to riverine conditions. Depending on nothing but their accumulated fat for migration to their spawning grounds, delays can seriously impact eels by wasting precious energy resources needed for a successful trans-Atlantic migration

New fluoroethyl phenylalanine analogues as potential LAT1-targeting PET tracers for glioblastoma

Abstract The use of O-(2-[18F]fluoroethyl)-l-tyrosine ([18F]FET) as a positron emission tomography (PET) tracer for brain tumor imaging might have some limitations because of the relatively low affinity for the L-type amino acid transporter 1 (LAT1). To assess the stereospecificity and evaluate the influence of aromatic ring modification of phenylalanine LAT1 targeting tracers, six different fluoroalkylated phenylalanine analogues were synthesized. After in vitro Ki determination, the most promising compound, 2-[18F]-2-fluoroethyl-l-phenylalanine (2-[18F]FELP), was selected for further evaluation and in vitro comparison with [18F]FET. Subsequently, 2-[18F]FELP was assessed in vivo and compared with [18F]FET and [18F]FDG in a F98 glioblastoma rat model. 2-[18F]FELP showed improved in vitro characteristics over [18F]FET, especially when the affinity and specificity for system L is concerned. Based on our results, 2-[18F]FELP is a promising new PET tracer for brain tumor imaging

Emigration of European silver eel (Anguilla anguilla L.) from a polder system into the Schelde estuary

Connectivity between freshwater habitats and marine areas is heavily obstructed by migration barriers, leading to a high pressure on diadromous eel populations. Migration barriers attribute to the 98% decline of the European eel (Anguilla anguilla L.) population. A better understanding of eel behaviour regarding these barriers is needed for water managers to take proper mitigation actions. We tracked 50 eels by means of acoustic telemetry between July 2012 and January 2015 and analysed their migration behaviour in a Belgian polder area. On their way to the Schelde Estuary, eels face several migration barriers such as a pumping station, a weir and tidal barriers. The telemetry study did reveal significant delays and searching behaviour near those barriers. Depending on nothing but their accumulated fat, delays can have a serious impact on the fitness of the eel by wasting precious energy resources needed for a successful trans-Atlantic migration. In addition, delays and searching behaviour can also increase predation risk. The obtained knowledge can contribute to efficient management such as improved fish passage and guidance solutions

Cost-effectiveness and screening performance of ECG handheld machine in a population screening programme: The Belgian Heart Rhythm Week screening programme

Aims Overall, 40% of patients with atrial fibrillation are asymptomatic. The usefulness and cost-effectiveness of atrial fibrillation screening programmes are debated. We evaluated whether an atrial fibrillation screening programme with a handheld electrocardiogram (ECG) machine in a population-wide cohort has a high screening yield and is cost-effective. Methods We used a Markov-model based modelling analysis on 1000 hypothetical individuals who matched the Belgian Heart Rhythm Week screening programme. Subgroup analyses of subjects &gt;= 65 and &gt;= 75 years old were performed. Screening was performed with one-lead ECG handheld machine Omron (R) HeartScan HCG-801. Results In both overall population and subgroups, the use of the screening procedure diagnosed a consistently higher number of diagnosed atrial fibrillation than not screening. In the base-case scenario, the screening procedure resulted in 106.6 more atrial fibrillation patient-years, resulting in three fewer strokes, 10 more life years and five more quality-adjusted life years (QALYs). The number needed-to-screen (NNS) to avoid one stroke was 361. In subjects &gt;= 65 years old, we found 80.8 more atrial fibrillation patient-years, resulting in three fewer strokes, four more life-years and five more QALYs. The NNS to avoid one stroke was 354. Similar results were obtained in subjects &gt;= 75 years old, with a NNS to avoid one stroke of 371. In the overall population, the incremental cost-effectiveness ratio for any gained QALY showed that the screening procedure was cost-effective in all groups. Conclusions In a population-wide screening cohort, the use of a handheld ECG machine to identify subjects with newly diagnosed atrial fibrillation was cost-effective in the general population, as well as in subjects &gt;= 65 and subjects &gt;= 75 years old

Measuring serotonin synthesis: from conventional methods to PET tracers and their (pre)clinical implications

The serotonergic system of the brain is complex, with an extensive innervation pattern covering all brain regions and endowed with at least 15 different receptors (each with their particular distribution patterns), specific reuptake mechanisms and synthetic processes. Many aspects of the functioning of the serotonergic system are still unclear, partially because of the difficulty of measuring physiological processes in the living brain. In this review we give an overview of the conventional methods of measuring serotonin synthesis and methods using positron emission tomography (PET) tracers, more specifically with respect to serotonergic function in affective disorders. Conventional methods are invasive and do not directly measure synthesis rates. Although they may give insight into turnover rates, a more direct measurement may be preferred. PET is a noninvasive technique which can trace metabolic processes, like serotonin synthesis. Tracers developed for this purpose are α-[11C]methyltryptophan ([11C]AMT) and 5-hydroxy-L-[β-11C]tryptophan ([11C]5-HTP). Both tracers have advantages and disadvantages. [11C]AMT can enter the kynurenine pathway under inflammatory conditions (and thus provide a false signal), but this tracer has been used in many studies leading to novel insights regarding antidepressant action. [11C]5-HTP is difficult to produce, but trapping of this compound may better represent serotonin synthesis. AMT and 5-HTP kinetics are differently affected by tryptophan depletion and changes of mood. This may indicate that both tracers are associated with different enzymatic processes. In conclusion, PET with radiolabelled substrates for the serotonergic pathway is the only direct way to detect changes of serotonin synthesis in the living brain