Head shape disparity impacts pollutant accumulation in European eel

Endangered, exploited glass eels (Anguilla anguilla) with critical levels of heavy metals and microplastics reveal both shipping and plastic spill threats

In the life of the endangered but still fished Anguilla anguilla, glass eels are recruited through estuaries. These fragile ecosystems are among the most disturbed on the planet. Here, heavy metals and microplastics were measured in estuary water and European glass eels entering bay of Biscay rivers of different size and anthropogenic stress. Eels from all the estuaries exhibited cadmium exceeding legal European limits, as happened with lead in samples from the highly disturbed Avilés estuary. Several water samples from small rivers surpassed the estimated limit of microplastic for ecotoxicological safety. In multiple regression analysis, both eel lead and microplastic content were significantly explained from shipping activity in the estuaries. Eel cadmium content was not associated with estuary stressors, being probably acquired during the oceanic migration of eel larvae. The presence in eels of new white polyethylene particles that had not been found previously in the region could be explained from the marine plastic spill of "Toconao" cargo in December. The same spill could explain a significant increase of microplastic bioconcentration in the glass eels in comparison with previous surveys. These risks for critically endangered eels, and for the consumers, highlight the urgent need for reducing the impact of contaminants on both local and global scales.

Influence of 17α-Methyltestosterone on Morphological Deformities and Pigmentation Development in Juvenile Japanese Eels, Anguilla japonica

17α-methyltestosterone (MT) is a synthetic steroid used to induce masculinization when administered during the larval stage of fish. However, the side effects of MT on eel are still poorly understood and, in this study, we examined the various effects of MT on juvenile eel A. japonica (100.63 ± 8.56 mm total length (TL)). To further investigate growth and sex differentiation, juvenile eels (n = 1000) were exposed to 25 µg/g MT for 6 months. We analyzed growth-related factors, sex steroid hormones, skin pigmentation, and color-related gene expression. Through this study, we found a 90% sex conversion of juvenile eels to males using MT treatment. In the MT-treated eel group (285.97 ± 26.21 mm TL) where sexual maturity was induced, spermatogonia stages were observed in the gonads. In contrast, the control group (395.97 ± 27.72 mm TL) exhibited an 80% immaturity rate, with only 20% of the subjects that were rapidly developing displaying early oogonia. ELISA analysis results showed that the level of growth hormone, which is known to be secreted from spermatogonia, did not change as a result of MT treatment. We confirmed that MT delayed growth and caused morphological changes, particularly a shortened snout length and pigmentation of the fin. The total length, body weight, and snout length were considerably lower in the experimental group than in the control group. In addition, in histological analysis we also observed that some of the MT-treated group (5 out of 10 fish) showed liver atrophy and inflammation, and physiological analysis showed that the cortisol concentration increased in the MT-treated eels. Interestingly, we found that some pigment color-related genes, such as melanocortin 1 receptor (MC1R), tyrosinase (Tyr), and dopachrome tautomerase (DCT), were significantly overexpressed in the fins of MT-treated eels. These results suggest that the treatment of A. japonica larvae with MT induced masculinization but also causes growth side effects from the use of synthetic hormones.

European eels and heavy metals from the Mar Menor lagoon (SE Spain)

Heavy metal pollution is related to the fall in European eel (Anguilla anguilla) populations. The Mar Menor lagoon (SE Spain) is home to an endangered population of this species, which is still caught for human consumption. The presence of Pb, Cd and Hg in the livers and muscles and the Se:Hg ratio in muscle of 150 eels from this lagoon were determined. Pb concentrations were higher than those reported from other populations in the world, while Cd and Hg concentrations in the tissues analysed were lower. In terms of food safety, Se concentrations play an important role in sequestering Hg in eels from this lagoon.

Quality assessment of escaping silver eel (Anguilla anguilla L.) to support management and conservation strategies in Mediterranean coastal lagoons

Silver eel samples, collected from the lagoons of Fogliano and Caprolace (Italy), were investigated for a broad range of contaminants (29 polychlorinated biphenyls, 9 polybrominated diphenyl ethers, 5 dichlorodiphenyltrichloroethane, 5 chlordanes, hexachlorobenzene, 3 hexachlorocyclohexane, and 5 metals). Concentrations of targeted compounds stand for a general low contamination pattern. Infestation by Anguillicola crassus and virus infections were also examined. No parasite infestation was found, while infected silver eels had a low prevalence for EVEX, and, for the first time in the Mediterranean area, for AngHV-1. Overall, a good quality status of escaping silver eels, for both lagoons, was highlighted by the use of integrative Indexes. A quality assessment of the ecological status of the two lagoons was carried out developing an expert judgment approach, in order to characterize the habitat of eel stocks. A Final Pressure Index was derived, whose values showed an overall limited global anthropogenic impact acting on both lagoons. Results stand for the suitability of an integrated approach to assess lagoon habitats and eel local stocks quality. This could be proposed as a tool to identify sites yielding high quality eel spawners in the Mediterranean region, in order to set up suitable management frameworks, providing elements to appraise and discuss the potential of coastal lagoons in the Mediterranean region towards the recovery of the eel global stock.

Saving the European Eel: How Morphological Research Can Help in Effective Conservation Management

The European eel (Anguilla anguilla) is a critically endangered species, whose recruitment stocks have declined to nearly 1% compared to the late 70s. An amalgam of factors is responsible for this, among them migration barriers, pollution, habitat loss, parasite infection, and overfishing. A lot of recent studies focus on aspects that can increase the mature silver eel escapement rate, such as identifying migration barriers and developing passageways or addressing the impact of pollution on the eel's health. However, little attention is given to the eel's morphology in function of management measures. Worryingly, less than 50% of the currently installed management plans reach their goals, strongly indicating that more information is needed about the eel's ecology and behavior. Functional morphological studies provide insights on how species perform behaviors crucial for survival, such as feeding and locomotion, but also in how environmental changes can affect or limit such behaviors. Consequently, functional morphology represents an important biotic component that should be taken into account when making conservation decisions. Hence, here, we provide an overview of studies on the eel's morphology that do not only demonstrate its relation with ecology and behavior, but also provide information for developing and installing proper and more specific management measures.

Applied Functional Biology: Linking Ecological Morphology to Conservation and Management

Many researchers work at the interface of organisms and environment. Too often, the insights that organismal, or functional, biologists can bring to the understanding of natural history, ecology, and conservation of species are overlooked. Likewise, natural resource managers are frequently focused on the management of populations and communities, while ignoring key functional traits that might explain variation in abundance and shifts in species composition at these ecological levels. Our intention for this symposium is two-fold: (1) to bring to light current and future research in functional and ecological morphology applicable to concerns and goals of wildlife management and conservation and (2) to show how such studies can result in measurable benchmarks useful to regulatory agencies. Symposium topics reveal past, present, and future collaborations between functional morphologists/biomechanists and conservation/wildlife biologists. During the SICB 2020 Annual Meeting, symposium participants demonstrated how data gathered to address fundamental questions regarding the causes and consequences of organismal form and function can also help address issues of conservation and wildlife management. Here we review how these, and other, studies of functional morphology, biomechanics, ecological development morphology and performance can inform wildlife conservation and management, principally by identifying candidate functional traits that have clear fitness consequences and population level implications.