Spatial distribution of an eel population (Anguilla anguilla L.) in a small coastal catchments of northern Brittany (France). Consequences hydraulic works.

The Frémur is a 60 km2 catchment of Brittany where many hydraulic works (dams, weirs, gauging structures, etc.) have reduced the recruitment by elvers and glass eels since at least 50 years. In 1992, an eel lift was built on the main dam (14 m high) and in 1996, two other dams (5 m high) located downstream were equipped with eel passes to improve upstream migration. In 1995, before the construction of the passes, eel population parameters (density, biomass and size distribution) were assessed at the scale of the whole watershed by electrofishing (removal method) in 33 stations. The average biomass was high (19 g/m2 ) despite the numerous physical obstructions. However, there was an accumulation of eels downstream many hydraulic works and very low densities immediately upstream. Moreover, downstream the first obstruction, at 2 km from the sea, the population is dominated by boot lace eels and elvers (< 100 mm), whereas this size class is absent in upstream reaches. These results suggest that the standing capacity of the watershed is not reached and that the population could be enhanced in the next years by the recently installed eel passes

Importance of specific fish passes for European eel (Anguilla anguilla L.) recruitment

The Frémur is a small catchment in Brittany (France) where many hydraulic works (dams, etc.) have reduced the recruitment by elvers and glass eels of the European eel population (Anguilla anguilla L.) for at least the last 50 years. A long-term study (from 1997 to 2003) of the two most important eel passes has shown that pass characteristics and location in the catchment have a major influence. A total of 105 000 eels were caught, and from 2000 to 25 000 eels colonised the river per year. Moreover, the size classes of eels caught in the two passes were significantly different. Eels were larger (mean length 135 mm) in the downstream pass than in the upstream pass (mean 118 mm). Management of hydraulic works by specific eel passes helps maintain eel colonisation upstream of a major obstacle in many catchments. This management can explain the maintenance of eel populations in many sectors close to the sea. However, the location of these works on the migration paths is essential for population parameters upstream

Journées Techniques nationales, 5 e édition Détection de l'agent rosette Sphareothecum destruens dans les communautés piscicoles de France (Projet Rosetta)

International audienceEn 2005, un risque d’émergence d’une maladie impactant la biodiversité des poissons d’eau douce a été identifié en Europe et associé à l’introduction du goujon asiatique Pseudorasbora parva (temminck & schlegel, 1846), qui est porteur sain d’un agent pathogène proche des champignons, l’agent rosette Sphaerothecum destruens (arkush, Mendoza, adkison & hedrick, 2003). Ce pathogène, qualifié de généraliste, est capable d’infecter de nombreuses espèces de poissons (hôtes) et d’entraîner des mortalités plus ou moins sévères. il semblerait que la première introduction de goujon asiatique en France ait eu lieu entre 1978 et 1979 dans la région de Beaumont-sur-Sarthe depuis des populations en provenance d’Albanie. Le projet Rosetta a eu pour objectif de cartographier la distribution de l’agent rosette sur différents cours d’eau français. Dix sites comprenant des populations de goujon asiatique et répartis sur l’ensemble du territoire métropolitain ont été échantillonnés entre 2017 et 2019. De l’ADN a été extrait des organes (foie, rate et reins) de goujons asiatiques, mais également de plusieurs espèces autochtones et allochtones (anguille européenne, barbeau fluviatile, bouvière, brème, carassin, chevaine, gardon, hotu, perche, perche soleil, poisson-chat, rotengle, truite commune, vairon) afin de déterminer par PCR quantitative la présence et l’abondance du pathogène. Alors que l’introduction de l’agent rosette en France est passée inaperçue pendant plus de 40 ans, notre étude montre que l’agent infectieux est bien présent dans plusieurs cours d’eau. Des espèces natives sont infectées avec des prévalences allant de 2 à 20%. De nouvelles espèces, comme la bouvière Rhodeus amarus (Bloch, 1782), le vairon Phoxinus phoxinus (linnaeus, 1758) ou encore le goujon Gobio gobio (Linnaeus, 1758), ont été identifiées pour la première fois comme hôtes potentiels du pathogène. La première recommandation est l’isolement des populations de goujon asiatique et le contrôle des transferts de poissons entre les zones déjà infectées et les zones non-infectées. La seconde recommandation est une communication publique des risques, afin d’inclure un maximum d’acteurs (dont les professionnels pisciculteurs, propriétaires d’étangs et pêcheurs amateurs) dans la lutte contre la propagation de cette maladie

Towards unravelling the Rosette agent enigma: Spread and emergence of the co-invasive host-pathogen complex, Pseudorasbora parva-Sphaerothecum destruens

International audienceThe emergence of non-native fungal pathogens is a growing threat to global health, biodiversity, conservation biology, food security and the global economy. Moreover, a thorough understanding of the spread and emergence of pathogens among invasive and native host populations, as well as genetic analysis of the structure of co-invasive host populations, is crucial in terms of conservation biology and management strategies. Here we com-bined extensive catchment sampling, molecular detection tools and genomic signatures to i) assess the prevalence of the rosette agent Sphaerothecum destruens in invasive and native fish populations in contrasting french regions, and ii) characterize the genetic diversity and population structure of its co-invasive and asymptomatic carrier Pseudorasbora parva. Although S. destruens was not detected in all the fish collected its presence in contrasting freshwater ecosystems suggests that the disease may already be widespread in France. Furthermore, our results show that the detection of S. destruens DNA in its asymptomatic carrier P. parva is still limited. Finally, we found that P. parva populations show a homogeneous genetic and geographical structuring, which raises the possibility of the occurrence of successive introduction events in France from their native and invasive range