G lugea sp. infecting Sardinella aurita in Algeria

Abstract

Parasitological examination of the commercially important pelagic fish Sardinella aurita Valenciennes, 1847 (Clupeidae) from the Eastern coast of Algeria revealed xenomas in the peritoneal cavity, suggesting a microsporidian infection. The prevalence of the disease was approximately 30% on average, higher in smaller individuals and showing significant seasonal variation. The xenomas contained numerous ellipsoidal spores, surrounded by a dense layer of connective tissue. Spore sizes were 6.10 ± 0.38 µm length and 3.54 ± 0.43 µm width. Ultrastructural examination by transmission electron microscopy showed various development stages of the parasite, including meronts, sporonts, sporoblasts and mature spores. The internal organization of the mature spores, with a single nucleus, prominent posterior vacuole, a lamellar polaroplast and an isofilar polar tube arranged in a single row, was typical of the genus Glugea. The DNA sequence of the small subunit ribosomal RNA gene confirmed that this parasite belongs to the genus Glugea. Genetic and morphologic comparison with G. sardinellensis, a species previously described in the same host from Tunisia shows many similarities, although some molecular and morphometric inconsistencies precluded the unambiguous assignment of our samples to G. sardinellensis. At the same time, we do not find sufficient grounds to erect a new taxon for our parasite. We discuss the implications of our findings for the current state of the systematics of Glugea.

Keywords: Algeria; Glugea; Histology; Microsporidia; SSU rDNA; Sardinella aurita; Ultrastructure.

Fig. 1

Parasitogical indexes for Microsporidian Glugea sp. according to seasons (A) and size classes (B)

Fig. 2

Macroscopic and microscopic manifestation of the infection of S. aurita from Algeria with Glugea sp. A–C: Dissected abdominal cavity showing large (A, B) and small (C) xenomas. D Haematoxylin–Eosin stained smear showing mature spores. E Histological section of xenoma stained with Haematoxylin–Eosin S: spores, Xw: xenoma wall. Scale bars: A 10 mm, B, C 5 mm, D 10 μm, E 100 μm

Fig. 3

Ultrastructure (transmission electron microscopy) of different stages of the microsporidian Glugea sp. collected from Sardinella aurita in Algeria. A Meront with a single nuclei (N), surrounded by a simple plasma membrane, B Sporont with nucleus (N), surrounded by a thick plasma membrane, C Sporoblast, with a developoing external exospore (Ex) D–G immature spores surrounded by an undulating exospore (Ex), often folding into conspicuous projections (Pr), H longitudinal section of mature spore showing anchoring disc (Ad), polar filament coils (Pfc) with 16 coils, posterior vacuole (Pv), exospore (Ex) and endospore (En), I Detail of the spore wall and polar filament coils. Scale bars: A, B, C, D, F, G: 200 nm, E: 100 nm, H: 400 nm, I: 50 nm

Fig. 4

The ML tree with the highest log likelihood (-5048.68) is shown. The percentage of trees in which the associated taxa clustered together (i.e. Bootstrap support) is shown next to the branches. Initial tree(s) for the heuristic search were obtained automatically by applying Neighbor-Join and BioNJ algorithms to a matrix of pairwise distances estimated using the Maximum Composite Likelihood (MCL) approach, and then selecting the topology with superior log likelihood value. A discrete Gamma distribution was used to model evolutionary rate differences among sites (5 categories (+ G, parameter = 0.3101). The tree is drawn to scale, with branch lengths measured in the number of substitutions per site