Synchronization of occurrence of the ovarian philometrid, Philometra carolinensis, with the spawning season of its fish host, the spotted seatrout, Cynoscion nebulosus

The philometrid Philometra carolinensis inhabits the ovaries of the spotted seatrout, Cynoscion nebulosus. A 2-year study in estuaries of South Carolina showed that each year adult female worms were present only during the spawning season of the host and that only sexually mature fish were infected. Overall prevalence was 13.1%. Young-of-the-year fish were uninfected and mature 1-year-old fish were less frequently infected than older fish. Abundance of the philometrid was significantly different in age-1 and -2 spotted seatrout. Prevalence, mean abundance, and intensity peaked during the first 2 months of the host’s 4-month spawning season, which then declined abruptly. Occurrence of the philometrid in the fish host was unaffected by water temperature, salinity, and dissolved oxygen. Histological studies revealed that the worms were hematophagous. Worms induced disruption of the ovarian lamellar walls resulting in the interruption of development and the loss of host eggs into the ovarian lumen prior to their maturation. The data show that development of this parasite is linked to the host’s reproductive status and suggest that paratenesis plays an important role in the maintenance of the parasite’s life cycle.