Abstract: Caenorhabditis elegans,as a good model organism,has been used in the study of resistant mechanism against anthelmintics.On the other hand,formalin has been widely used in prevention and cure of fish parasites.However,many parasites generate resistance to formalin because of long term application.In the present study,techniques of suppression subtractive hybridization and dot blot hybridization were applied to analyze the gene expression alteration in C.elegans after formalin stimulation.C.elegans was serially cultivated in medium containing 800ppm formalin for one month.The worms growing in medium containing formalin was served as experimental group while those growing in normal medium as control group.Total RNA was extracted;mRNA was purified and reversely transcribed into cDNA.Forward suppression subtractive hybridization was used to deduct the cDNA contained in the control group out of the experimental group to enrich differential expression genes.Then,dot blot hybridization was used to further screen the up-regulation genes after formalin stimulation.The control cDNA and subtractive cDNA libraries were employed as probes,respectively,to hybridize with PCR product of the subtractive clones.It was found that 161 out of 676 gene clones showed evident expression discrepancy,and then they were sequenced after dot blot hybridization.BLAST analyses indicated the following genes up-regulated:(1) apoptosis related genes,encoding mitochondrial respiratory chain related proteins,protein SGT-1 containing TPR motif,heat shock proteins,oxidative stress related proteins,endocytosis related proteins,DNA duplication and reparation related proteins and other important apoptosis related proteins;(2) genes encoding important transcription regulation factor and signal transduction related proteins,for example,transcriptional activation factor FosB/c-Fos,G protein,cyclin B,Ca-binding protein,and nucleosome assembly protein NAP-1;(3) genes participating in energy,protein,fat and amino acid metabolisms;and(4) some genes encoding unnamed proteins.It indicates that,besides inducing apoptosis,formalin also impacts C.elegans' cell metabolism.