Philometra rubra (Nematoda: Philometridae) — first description of the male from striped bass (Morone saxatilis) and implications for re-introduction of an extirpated population

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Philometra rubra (Leidy, 1856) is a pathogenic parasitic nematode infecting striped bass (Morone saxatilis (Walbaum, 1792)) in eastern North America. Identification of philometrids is difficult, male P. rubra have never been found, and transmission is poorly understood. To re-establish the “Extirpated” striped bass population in the St. Lawrence Estuary (SLE), Quebec, young-of-the-year (YOY) striped bass from the Miramichi River, New Brunswick, were collected and released into the SLE. The present study was undertaken to find Philometra in striped bass from the Miramichi River, for identification, description, and examine transmission and lesions. Philometra rubra was identified in 100% of 32 YOY (intensity = 26–125) and 100% of nine 1-year-old (intensity = 4–25 in five striped bass) striped bass collected in summer 2011. The swim bladder and body cavity were sites of infection in YOY with no tissue response observed histopathologically. Gravid P. rubra females occurred in the body cavity and swim bladder, with males predominately in the latter site. Males were short-lived, being absent in 1-year-old bass. Adult male and adult female P. rubra are described. Males of P. rubra can be distinguished from other described species based on spicule, gubernaculum, and body-length measurements. This parasite may have implications for the re-introduction program and conservation of striped bass in the SLE and in other populations.