The red swamp crayfish Procambarus clarkii is an important freshwater economic crayfish in Chinese inland due to its high market value and consumer demand. The sexual precocity in this species has received considerable attention in recent years because more and more individuals matured at small sizes, which devalues the commercial production. In this study, by the full-length normalization subtractive hybridization (FNSH) method we identified 16 differently expressed sequences between precocious and normal grown P. clarkii ovaries. Of the down-regulated sequences in precocious ovaries, one encodes a peptide which shared the highest identity to C1q-like family and contained a typical C1q domain at the C-terminal, thus it was named PcC1q-like. QRT-PCR analysis showed that PcC1q-like was transcribed specifically in ovary, with higher expression level in vitellogenic stages. In situ hybridization exhibited specific expression of PcC1q-like in follicular cells around the vitellogenic oocytes. Knockdown of PcC1q-like by injection of double strand RNA (dsRNA) resulted in disruption of follicular cells, decreased transcripts of vitellogenin (Vg) and vitellogenin receptor (VgR), and reduced progesterone content. These results suggest that PcC1q-like may promote ovarian development by stimulating the synthesis and transportation of vitellogenin into oocytes. These data provide insights into the molecular regulatory mechanisms of sexual precocity and ovarian development in crustaceans. Statement of relevance: The red swamp crayfish Procambarus clarkii is one of the most important freshwater aqua culture species in Chinese inland. We screened 16 sequences that are potentially involved in sexual precocity of P. clarkii. One candidate was demonstrated to be a novel ovary-specific C1q-like gene of P. clarkii, thus named PcC1q-like. Knockdown of PcC1q-like resulted in disruption of follicular cells, decreased transcripts of Vg and VgR, and reduced progesterone, suggesting its essential role in vitellogenic ovarian development of P. clarkii. (C) 2016 Elsevier B.V. All rights reserved.