Host-dependent vitality of juvenile freshwater mussels: Implications for breeding programs and host evaluation

This study assessed the differences in nutrition delivered to juveniles of two European freshwater mussel (Unionidae, Bivalvia) species with different levels of host specificity (Unio crassus and Anodonta anatina) developing on several potential host fish species. Juveniles were obtained, and the transformation success rate (the proportion of successfully transformed glochidia) was determined after experimental infestations under laboratory conditions. Juvenile lipid reserves were assessed via an epifluorescence method (Nile Red staining) and compared among different host fish species and individuals. The juveniles of both species developing on different hosts significantly differed in their lipid reserves as indicated by fluorescence activity. Moreover, juvenile growth during the early post-parasitic stage was different among host fish species, congruently with the results of lipid quantification. No clear general linkage was recorded between the quantitative (transformation success rate) and qualitative (lipid reserves) indicators of juvenile success. In the case of U. crassus, the host fish species that had the highest glochidium transformation success rate (Phoxinus phoxinus) also produced juveniles with significantly higher levels of lipid reserves compared with the other hosts. In contrast, a positive association between quantitative and qualitative indicators of juvenile success was not observed in the experiment with A. anatina suggesting that the conditions influencing the mortality of glochidium larvae during the parasitic phase and their energy uptake may have a different basis. The observed persisting effects of the fish-associated larval conditions on early juvenile stages might have critical consequences for the vitality and survival of juvenile freshwater mussels during the early post-parasitic stage, with implications for the effectiveness of breeding programs and strategies for host selection. A more thorough incorporation of the qualitative measures of the host fish value can lead to the further optimization of culturing protocols (improved nutrition reserves and growth of juveniles) and to setting more accurate management goals for host resources under field conditions. (C) 2015 Elsevier B.V. All rights reserved.