To understand the molecular mechanism associated with growth variability in bivalves, the Solexa/Illumina technology was employed to analyze the transcriptomic profiles of extreme growth rate differences (fast- VS. slow-growing individuals) in one full-sib family of the ark shell Scapharca subcrenata. De novo assembly of S. subcrenata transcriptome yielded 276,082,016 raw reads, which were assembled into 98,502 unique transcripts by Trinity strategy. A total of 6,357 differentially expressed genes (DEGs) were obtained between fast- and slow-growing individuals, with 580 up-regulated expression and 5777 down-regulated expression. Functional annotation revealed that the largest proportion of DEGs were classified to the large or small subunit ribosomal protein, all of which showed significantly lower expression levels in fast-growing group than those in slow-growing group. GO enrichment analysis identified the maximum of DEGs to biological process, followed by molecular function and cellular component. Most of the top enriched KEGG pathways were related to energy metabolism, protein synthesis and degradation. These findings reveal the link between gene expression and contrasting phenotypes in ark shells, which support that fast-growing individuals may be resulted from decreased energy requirements for metabolism maintenance, accompanying with greater efficiency of protein synthesis and degradation in bivalves.