TLR9, a member of the Toll-like receptor family, plays a key role in the innate immune system by identifying the DNA CpG motif of bacteria and viruses. Using rapid amplification of cDNA ends (RACE), we cloned the full length L., Abbr. Ca). We then evaluated the effects of exogenous hCG and gonad development on CacDNA was 3 509 bp in length with a 3′-untranslated region (242 bp), a 5′-untranslated region (72 bp), and a 3 195 bp open reading frame (ORF). The ORF of CacDNA encodes a 1 064 amino acid protein with a signal peptide of 19 amino acids, 15 leucine rich repeat (LRR) motifs, one transmembrane zone, and one Toll/IL-1 receptor (TIR) domain. The amino acid sequence of CaTLR9 possessed 92%, 83% and 79% identity with the TLR9s of , respectively. The expression level of was highest in the spleen of crucian carp, followed by the kidney and gill. The level of expression was low in the remaining tissues. The expression of was higher during the breeding season than the non-breeding season. Additionally, injections of exogenous hCG significantly up-regulated the expression of TLR9 is a new candidate target gene for investigating non-specific immunity in crucian carp and improving the health of cultured fish.