1. Coextinction is the simplest form of secondary extinction and freshwater mussels
(Bivalvia, Unionida) may be particularly prone to this phenomenon as their life
cycle includes an obligatory parasitic larval stage on fish hosts.
2. The main aims of this study were to determine the possible ecological fish hosts
of Anodonta anatina (Linnaeus, 1758) in several rivers of the Douro basin in northern
Portugal and to assess possible spatial and temporal differences in glochidial
(larval) loads. In order to achieve this, electrofishing was conducted from
December to April, the fish fauna was characterized, and levels of infestation with
A. anatina glochidia were determined.
3. Native cyprinid species, mainly Luciobarbus bocagei (Iberian barbel) and Squalius
carolitertii (northern Iberian chub), together with the non-native Lepomis gibbosus
(pumpkinseed sunfish) and Alburnus alburnus (common bleak), were found to have
the highest glochidial loads. Clear differences in infestation between rivers and
throughout time were detected, with an infestation period from January to
March, and with the Tâmega River having the highest prevalence.
4. Anodonta anatina is able to infest a variety of fish species, and this together with
earlier studies showed that the metamorphosis into juveniles occurs mainly in
native cyprinid species, although non-native species like common bleak can also
be considered suitable hosts. However, the larvae infesting other non-native species,
such as the pumpkinseed sunfish, do not metamorphose and can be considered
‘dead ends’.
5. Overall, the results reported here are important for the conservation of A. anatina
(and other unionoid species) because several Iberian rivers (and worldwide) have
been subjected to the extirpation of native fish species and the introduction of
non-native fish species. Therefore, careful assessments of fish communities
should be conducted to assess possible negative interactions with freshwater
mussels.
This work was supported by the Fundaç~ao para a Ciência e Tecnologia
(FCT), project 3599 ‘Promote the Scientific Production and Technological
Development and Thematic 3599-PPCDT’ by European
Regional Development Fund (FEDER) as part of the project FRESHCO
‘Multiple implications of invasive species on Freshwater Mussel
coextinction processes’ (contract: PTDC/AGRFOR/1627/2014). FCT
also support MLL with a doctoral grant (SFRH/BD/115728/2016).
We acknowledge the two anonymous referees for the helpful suggestions
that improved the clarity of our manuscript.
