An undescribed, cryptic species of Didymocystis, as determined from sequences of 2 ribosomal genes and superficially similar to Didymocystis scomberomori (MacCallum and MacCallum, 1916), infected the skin of the Spanish mackerel, Scomberomorus maculatus, in the north-central Gulf of Mexico (GOM). An analysis of 558 fish from 2011 to 2013 from Louisiana, Mississippi, Alabama, and the Florida panhandle showed the prevalence of the trematode varied both spatially and temporally but not with sex of the fish host. Month, year, and geographic location were identified by a negative binomial generalized linear model as indicators of the abundance and intensity of infection. Prevalence, abundance, and intensity of infection were greatest in spring and fall months off the Florida panhandle. Furthermore, the abundance and intensity of infection correlated negatively with fork length, weight, and gonad weight of mature fish but positively with longitude. Therefore, smaller adult fish tended to be more infected than larger adults, and prevalence and intensity increased from west to east (Louisiana to Florida). Spatial and temporal trends seemed to result from physical factors (e.g., water temperature, salinity, bottom type), but they also coincided with the annual migration of S. maculatus as fish moved northward along the GOM coastline from the southern tip of Florida in the spring months and returned in the fall, being present in the north-central GOM from late spring through fall. This pattern suggests the possibility that acquisition of infections occurred from a molluscan host in waters off the Florida panhandle.

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