Ultrastructure of Nucleospora cyclopteri, an intranuclear microsporidian infecting the Atlantic lumpfish (Cyclopterus lumpus L.)

Nucleospora cyclopteri is an intranuclear microsporidian parasite that has recently been described infecting wild Atlantic lumpfish from Iceland. A similar report was previously made from captive lumpfish in Canada, but it is not currently known whether the same parasite is responsible for both infections. Here we present new ultrastructural data on the Icelandic parasite in order to make direct comparisons with the Canadian report. Mature spores are elongate ovoid, contain a single nucleus, an isofilar polar filament with 10-12 turns and measured 2.53 x 1.04 mu m. The earliest developing stages observed were sporogonial plasmodia that contained aggregates of electron dense structures typical of microsporidia from the Enterocytozoonidae. These spore characteristics are almost identical to the Canadian form and both manuscripts report degenerate lymphocytes and comparable developing plasmodial stages. Due to these dose similarities, we condude that the same parasite, Nucleospora cyclopteri, is responsible for causing disease in both Canadian and Icelandic lumpfish populations.