Parasites of Acipenser brevirostrum LeSueur and Acipenser oxyrhynchus Mitchill (Osteichthyes: Acipenseridae) in the Saint John River Estuary, N.B., with a description of Caballeronema pseudoargumentosus sp.n. (Nematoda: Spirurida)

Eleven species of helminth and arthropod parasites are reported from Acipenser brevirostrum and Acipenser oxyrhynchus in the Saint John River estuary, N.B., Canada. Diclybothrium armatum, Spirorchis sp., Fessesentis friedi, and Argulus alosa are new records from A. brevirostrum. Derogenes varicus, Truttaedacnitis sphaerocephala, Echinorhynchus gadi, and Dichelesthium oblongum are new records from A. oxyrhynchus. Truttaedacnitis sphaerocephala and D. oblongum are new locality records for North America. Caballeronema pseudtiargumentosus sp.n. is described from A. brevirostrum and differs from the similar spirurid Ascarophis argumentosus in length of spicules (110–138 μm and 492–598 μm versus 81–86 μm and 320–340 m), egg length (38–44 μm versus 29–35 μm), and number of egg filaments (4–10 versus 2). Details of the oral structure of C. pseudoargumentosus are described and its relationship to Ascarophis and Capillospirura discussed. Parasite fauna of adult A. oxyrhynchus, juvenile A. oxyrhynchus, and A. brevirostrum are distinct and reflect differing life histories and ecologies of the hosts.