Freshwater mussels can potentially be used as indicator organisms for detection of pollution of toxic substances in freshwater ecosystems. One way of realizing this potential would be to identify biomarkers in the form of genes that respond by over- or under-expression when mussels are exposed to toxic pollutants. For monitoring of freshwater ecosystems in Sweden and many other European countries, Anadonta anatina has been identified as one of the most promising mussel species to use as indicator organism. However, currently the genome of A. anatina as not been sequenced and only a handful of genes have been targeted by traditional sequencing approaches. For example, the Genbank nucleotide sequence database currently contains just over 600 entries for A. anatina, although its genome would be expected to contain 10-20 thousand genes in total. We therefore recently carried out full transcriptome sequencing of samples from controls and from mussels exposed to toxic chemicals (80 samples in total) on the Illumina NovaSeq6000 platform, generating approximately 20-50 million reads per sample. In this project we will first perform quality control, filtering, and error correction of reads, followed by de novo assembly of the transcriptome for each sample that is of sufficient quality. Since the genome of A. anatina is largely unknown, characterization and annotation of the expressed genes using homology mapping approaches will be an important part of the project. Based on read counts, genes that are differentially expressed in a comparison between treated and untreated mussels will be identified and investigated for their potential as candidate biomarkers.