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.

Metamicrocotyla macracantha, a polyopisthocotylid gill parasite of the striped mullet, Mugil cephalus: population dynamics in South Carolina estuaries.

In the estuarine system of South Carolina (USA), the striped mullet, Mugil cephalus, was found to be parasitized by the polyopisthocotylid monogenean Metamicrocotyla macracantha among other gill parasites. Mullet of various ages were collected monthly for 1 year from oligohaline, mesohaline, polyhaline, and euryhaline localities. The population dynamics of M. macracantha was analyzed according to time of year, different salinity levels, and host age and sex. Out of the 770 mullet studied, 11.2% were infected (mean, two worms per host). Neither prevalence nor mean intensity was correlated with biotic factors. However, significant seasonal variation in prevalence was observed, and the worm was found more frequently in higher salinities. Mean intensity, however, did not change significantly with time of year or salinity. This is the first published report of M. macracantha in the South Carolina estuarine system and represents the northernmost record for this parasite. Furthermore, the lack of common egg-bearing individuals and juveniles indicated that this area is likely the northern limit of the geographical range of M. macracantha, whose life cycle seems restricted to more constant water temperatures than those found at the South Carolina latitudes.