Abstract
European eel (Anguilla anguilla) is a catadromous fish species that received substantial attention as its population has markedly declined in the last three decades. The possible causes of this decline include habitat fragmentation factors such as dams and weirs. In some cases, these obstacles are equipped with fish friendly passage devices that may select young eels according to their climbing behaviour. We tested how individual climbing tendency was related to the event of fishway passage experienced in the field and classified fish climbing profiles as climbing ‘leaders’, ‘followers’, ‘finishers’ and ‘no climbers’. Moreover, we analysed the brain transcription level of genes related to neurogenesis and synaptic plasticity and compared it to climbing profiles. We found that fish from the upstream segments of an impounded river had a higher climbing propensity. Their behaviour was also more repeatable throughout the whole test than the obstacle-naive fish from the downstream segment. Moreover, we found that boldly climbing ‘leaders’ had lower levels of transcription of synapse-related genes than the climbing ‘followers’. These differences could be related to coping styles of fish, where proactive ‘leaders’ express a routine and risky behaviour, whereas reactive fish need an environmental assessment before exploratory behaviour. Our study showed that differences in climbing propensity exist in glass eels separated by water obstacles. Moreover, eels could adopt climbing different strategies according to the way they deal with environmental stress and to the cognitive abilities they possess.
Highlights
European eel (Anguilla anguilla) is a catadromous species with a high phenotypic plasticity [1,2], occupying a wide range of European inland and estuarine ecosystems
Differences in climbing tendency were significant among sampling site groups, and the fish displaying extreme behaviour originated from the most upstream groups
It is still difficult to tease apart whether the association between fish distribution and climbing behaviour is due to selection or habituation, we undoubtedly demonstrate for the first time, to our knowledge, that fragmentation induced by humans lead to a strong downstream to upstream differentiation in climbing behaviour in eels
Summary
European eel (Anguilla anguilla) is a catadromous species with a high phenotypic plasticity [1,2], occupying a wide range of European inland and estuarine ecosystems. Leptocephali larvae migrate from the Sargasso Sea, their unique spawning ground, towards the European continental shelf [3] Once arrived, they metamorphose into glass eels (i.e. post-larval stage) and many of them continue their migration to reach the upstream zones of inland waters, where they settle down for their juvenile growth phase. In order to reach the upper tributaries, migrating eels need first to find the entrance of the pass and voluntarily express a willingness to climb, i.e. engage into the fishway and go out of the water They need to find the way through the fishway and be able to reach its upper zone, especially in case of long, steep and potentially energy demanding fish ladders. In the case of catadromous and panmictic eel species, fragmentation by weirs and dams could for instance generate phenotypically different eel population subsets below and above the obstacle
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
