Natural transfer of helminths of marine origin to freshwater fishes, with observations on the development of Diphyllobothrium alascense

Infective stages of helminths of 5 species that occur as adults in marine m ammals were found in burbot, Lota lota (L.) (Gadidae), from the lower Kusko kwim River (southwestern Alaska): Diphyllobothrium alascense Rausch et Will iamson, 1958; Pyramicocephalus phocarum (Fabricius, 1780); Corynosoma strum osum (Rudolphi, 1801); Corynosoma semerme (Forsell, 1901); and Pseudoterran ova decipiens (Krabbe, 1878). Some larval stages were obtained also from sm elt, Osmerus mordax dentex Steindachner, an anadromous fish important as pr ey of burbot. Burbot, which are freshwater fish, could become paratenic hos ts of those helminths by means of at least 3 interactions: by consuming mar ine fishes in brackish waters at river mouths, by feeding on marine fishes that enter lower reaches of rivers, or by preying on anadromous fishes as t hey migrate up livers. Consumption of burbot by people may result in infect ion by helminths of marine origin; of those recorded, only P. decipiens may be significantly pathogenic. Attempts to rear P. phocarum in dogs were uns uccessful. Plerocercoids of D. alascense, of very small size and found only in the gastric lumen of burbot, readily infected dogs. For study of their development, strobilae were obtained at intervals of 48 hr to 32 days posti nfection. In heavy infections, some strobilae developed slowly, while other s underwent rapid development.