Phoxinus

Esposito, Anaïs, Denys, Gaël P. J., Foata, Joséphine & Quilichini, Yann, 2024, Unclear host taxonomy hinders parasite studies: An up-to-date checklist of the protozoan and metazoan parasites of Phoxinus minnows (Teleostei: Leuciscidae), Journal of Fish Biology 105 (6), pp. 1501-1539 : 1533

4.3 | Phoxinus as valuable hosts for conservation biology of the endangered freshwater mussel Unio crassus

A systematic molecular identification of Phoxinus minnows in parasitological studies may also be of interest from a conservation biology perspective. Unio crassus is an endangered freshwater mussel ( Gastropoda: Bivalvia), with conservation status assessments ranging from “extinct in the wild” ( Lithuania and the Netherlands) to “least concern” ( Kazakhstan and Russia) ( Bolotov et al., 2020; Lopes-Lima et al., 2017; Soroka et al., 2021). Unionidae mussels have the particularity of having an obligatory parasitic glochidium stage living attached to gills of freshwater fish. Glochidia larvae of freshwater mussel were recovered in the wild only from France ( P. phoxinus and P. csikii ) and Sweden ( Phoxinus sp. 7 ) for U. crassus Philipsson, 1788 and from Spain ( P. septimaniae ) for an unidentified Unionidae ( Cruz et al., 2022; Lamand et al., 2016; Schneider et al., 2019), and experimental infections were successful also for Anodonta anatina (Linnaeus, 1758) ( Beggel & Geist, 2015; Kekäläinen, Pirhonen, & Taskinen, 2014). According to the literature, P. phoxinus has been found to be a primary host for U. crassus . However, except in France, where this parasite was found in the wild on this host in the Seine and Rhine river basins, the experimental infestations were conducted in Czech Republic and Germany, where the host species’ reassignment is uncertain ( P. phoxinus , P. csikii , P. cf. morella , P. cf. morella , or P. marsilii depending on the origin) ( Douda et al., 2012; Douda, 2015; Lamand et al., 2016; Schneider et al., 2017; Taeubert, Gum et al., 2012; Taeubert, Martinez et al., 2012). Molecular identification of the Phoxinus hosts would be of interest to gain a better understanding of these organisms' host range and specificity. It is known that compatibility between mussel strains and fish hosts is essential in the parasite – host interaction, and thus for the conservation and management of U. crassus ( Schneider et al., 2017) . U. crassus has a wide distribution range in Eurasia, but records of its glochidia on Phoxinus minnows are comparatively relatively few. There could thus be preferences of the glochidia toward one or several Phoxinus species, which would be difficult to assess without molecular identification of the host. For this reason, a reliable identification of Phoxinus hosts could provide valuable information for the conservation and management of endangered freshwater mussels.