Over the last few years, the hard clam, Mercenaria mercenaria , aquaculture industry in Wellfleet, Massachusetts has been threatened by disease. This new disease is similar to a disseminated neoplasia previously described in other bivalves including the soft-shell clam, Mya arenaria . It is identified by abundant, atypical hemocytes filling the vascular system. The disease affects both sub-market and market sized animals, and heavily infected clams do not remain burrowed in the sediment, eventually dying on the surface. Current diagnostic methods rely on histopathology to identify and quantify the neoplastic cells within the clam . This method is not only costly, but time consuming. A new molecular diagnostic method that would use an easily obtained, even non-lethal, sample of hemolymph is being developed for the detection of hemocytic neoplasia in hard clams.
For transcriptome comparison , hemolymph was collected from the adductor muscle sinus from 5 diseased and 3 healthy clams using a 3 ml syringe with a 20-gauge needle. The hemolymph was stored in RNAlater at -80 °C for RNA extraction and RNASeq . Transcriptome analysis showed upregulation of a DNA replication licensing factor MCM3-like (Minichromosome Maintenance Complex Component 3) in all sick individuals, but no production in healthy individuals. This protein was selected to create a species-specific reverse transcription quantitative real-time PCR (RT-qPCR) assay. Using archived hemolymph samples, molecular data will be correlat ed with histological diagnoses from the same individuals. T his new diagnostic can be used to diagnose and quantify the severity of hemocytic neoplasia in hard clams.