Recognizing the attachment site on the definite host is essential for obligate ectoparasites for their biological succession. Being such, Caligus fugu, a marine copepod parasite with broader specificity towards pufferfish Takifugu, has a clear predilection for the host and the attachment location. The infectious stage of the parasite attaches itself exclusively to its host's fins. But the processes behind such unique host-/organ specificity are still mostly unknown. In this project, de novo assembled transcriptome analysis was conducted for gene expression profiling of the three developmental stages (free living second nauplius, infective first copepodid, and parasitic second copepodid) of the non-model parasite C. fugu with a view to elucidating the parasite's host recognition mechanism toward host puffers. Analyses of the RNA-seq gene expression data helped to prepare candidate gene list responsible for such host finding behavior in C. fugu during the infective first copepodid stage.