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The microplastic loads in elvers of the critically endangered European eel Anguilla anguilla, sampled in the lower reaches of three English rivers, were very low (incidence: 3.3%, mean ± s.d.: 0.03 ± 0.18 particles) and did not vary with body length or between rivers. Particles were mostly black, polyolefins, fibres and fragments of size 101-200 μm. Current levels indicate a low contamination pressure locally and, consequently, management efforts might prioritise mitigating the effects of other stressors affecting the species., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

The temporal effects of ethanol preservation on the δ 13 C and δ 15 N values of tissues excised from European eel Anguilla anguilla were assessed. Preservation significantly enriched 13 C values of fin and mucus but not dorsal muscle. The 13 C enrichment occurred in the initial 15 days of preservation and was independent of initial eel mass. Tissue preservation effects on δ 15 N values were negligible. These tissue-specific isotopic shifts should be considered when ethanol-preserved eel samples are used., (© 2023 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Anthropogenic activities are increasingly threatening aquatic biodiversity, especially anadromous species. Monitoring and conservation measures are thus required to protect, maintain and restore imperilled populations. While many species can be surveyed using traditional capture and visual census techniques, species that use riverine habitats in a less conspicuous manner, such as sea lamprey Petromyzon marinus, can be more challenging to monitor. Sea lamprey larvae (ammocoetes) can spend several years in freshwater burrowed within soft sediments, inhibiting their detection and assessment. Here, we present a qPCR assay based on the detection of environmental DNA (eDNA) to identify the presence of ammocoetes burrowed in the sediment. We present an extensively validated method that ensured both species-specificity of the assay as well as the capacity to detect ammocoetes when abundances are low. Experiments on burrowing activity suggested that most of the DNA released into the sediment occurs during burrowing. Overall, we demonstrate this new molecular-based tool is an efficient and effective complement to traditional monitoring activities targeting larval stages of sea lampreys., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)

Ecological studies on the critically endangered European eel Anguilla anguilla often incorporate stable isotope analysis that typically uses dorsal muscle sampled from euthanised eels. To minimise the lethal sampling of imperilled populations, fin tissue and/or epidermal mucus can provide non-lethal alternatives to muscle. The results here indicate that δ 13 C and δ 15 N values of both eel fin and mucus are not significantly different from those of muscle and can be applied directly in comparative SI studies., (© 2022 The Authors. Journal of Fish Biology published by John Wiley & Sons Ltd on behalf of Fisheries Society of the British Isles.)