Establishment of the Life Cycle of <i>Philometroides seriolae</i> (Nematoda: Philometridae) Using Surrogate Copepod Intermediate Host

Abstract

Philometoides seriolae is a large nematode parasite in the skeletal musculature of Japanese amberjack Seriola quinqueradiata. ​Philometrid nematodes generally use copepods as the intermediate host. ​However, the life cycle of P. seriolae remains unknown, including its intermediate host. ​Instead of finding the true intermediate host from natural environments, we used the copepod Tigriopus japonicus as a surrogate host to experimentally complete life cycle of the nematode. ​Fresh first stage larvae were obtained from the uterus of mature P. seriolae from naturally infected Japanese amberjack. ​Tigriopus japonicus actively fed on hatched larvae, which established infection in the hemocoel at a consistently high rate. ​Twenty-three to 27 days later, the infected T. japonicus were fed to artificially produced juvenile Japanese amberjack. ​About 11 months later, adult female nematodes were recovered from the skeletal musculature of the experimentally infected fish. ​This is the first report of experimental completion of life cycle from hatched larvae to adults in marine philometrid species. ​It would take more than a year for P. seriolae females in the definitive host to be able to produce and disseminate larvae, as those recovered from the experimental fish were still young with eggs in the uterus.