Developmental stages and growth of Pseudocaligus fugu Yamaguti, 1936 (Copepoda: Siphonostomatoida: Caligidae) host-specific to Puffer

The post-embryonic development of the copepod Pseudocaligus fugu is described. This sea louse only parasitizes toxic pufferfish, and causes commercial loss of cultured Takifugu rubripes in Japan. Two naupliar, one copepodid and four chalimus stages preceding the adult are recognized in the species. The development pattern is similar to that of Caligus except for the suppression of leg 4 in the early chalimus phase. Pseudocaligus fugu lacks any preadult stage, as in Caligus, but contrasts with Lepeophtheirus species in which two preadult stages are reported. The nature of the metamorphic changes in size and even in degree of expression of articulations can occur without moulting. The validity of some chalimus stages recognized in Lepeophtheirus species is questioned. Growth and egg production in P. fugu were obtained in the laboratory. Pseudocaligus fugu attained adulthood 9 days after the infective copepodid attached to the host.