New Microsporidia, Glugea sardinellensis n. sp. (Microsporea, Glugeida) Found in Sardinella aurita Valenciennes, 1847, Collected off Tunisian coasts

A new microsporidia Glugea sardinellensis n. sp. found in the teleost fish Sardinella aurita Valenciennes collected from the Tunisian coasts. The parasite develops in a large xenomas measuring 1–16 mm in diameter and is generally visible with naked eye in the connective tissue around the pyloric caeca of the host. Xenoma were often rounded, but would be occasionally ovoid or irregular shape, generally creamy but rarely opaque, and filled with mature spores. The spores were unikaryotic pyriform measuring 5–5.5 (5.25±0.24) μm in length and 2.5–3 (2.75±0.24) μm in width. The posterior vacuole was large and occupied more than half of the spore. Ultrastructural study indicated that the mature spore has 13–14 coils of polar filament arranged in one layer, and a rough exospore. Intermediate stages were rare and randomly distributed in the xenoma. Merogonial and sporogonial stages were uni or binucleate. The plasma membrane surrounding the meront was irregular and indented. The mean prevalence was 18.3% and it varied according to season and locality. The distribution of prevalence according to fish size indicated that small fish were primarily affected. Phylogenetic analysis using the partial sequence of the SSU rDNA showed consistent association with species of the genus Glugea. The most closely related species was Glugea atherinae Berrebi, 1979 with 98.5% similarity.