SUMMARY Animal groups are integrated by emission of discrete signals from members,so-called social signals, which have evolved for each species. Among communication signals, chemical signals play an important role for recognition of group membership. The catfish Plotosus lineatus forms a dense school immediately after hatching, and school recognition is under the control of chemical signals emitted by the school members. The key substance(s)governing this recognition are deduced to be a mixture of phosphatidylcholines(PC). To substantiate this hypothesis that a mixture of PC molecular species functions as recognition of school-specific odor, we examined the ability of P. lineatus to discriminate between familiar and unfamiliar PCs. P. lineatus responded only to PCs from a familiar school, and not to those from unfamiliar schools. PC molecular species were then analyzed by quantitative high performance liquid chromatography, which resulted in not only a complex mixture of PC molecular species, but also school-specific PC profiles. Furthermore, multivariate analysis of the quantified PC peaks revealed the presence of various PC profiles. Finally, we showed that the modification of PC profiles disrupts the recognition of school odor in P. lineatus . Therefore, we conclude that the recognition of school odor in P. lineatus is governed by school-specific PC profiles.