Search

The ultrastructure of the developmental stages of Enteromyxum scophthalmi is described. Scarce intracellular, early uninucleated stages appeared within intestinal epithelial cells whereas proliferative stages were abundant both intraepithelially and in the intestinal lumen. In the proliferative stages, food reserves were abundant in the cytoplasm of P cells and consisted mostly of carbohydrates in the intraepithelial stages and lipid inclusions in the luminal stages. Sporogenesis could occur in enveloped cells or by direct division or clustering of generative cells. The abundance, shape and size of mitochondria as well as the number and shape of their cristae were very variable in the different developmental stages. The cristae were usually tubular and sometimes plate-like, discoidal or lamellar. True flat cristae were not observed. We found elements of closed (cryptomitosis) and open mitosis as well as structures reminiscent of microtubule organising centres, hitherto not described in myxosporeans. The significance of these findings is discussed in relation to the taxonomic and phylogenetic position of the Myxozoa.

The ultrastructure and cytochemistry of merogonial and gamogonial stages and early unsporulated oocysts of Goussia sparis in the intestine of Sparus aurata were studied. The typical pellicle was observed in some stages. The different stages might appear in intraepithelial or supraepithelial positions, but they were always intracellular. First steps of two apparently different endomerogonies were observed in intra- and supraepithelial positions, respectively. An apparent ectomerogony also occurred in supraepithelial stages. Developing macrogamonts showed surface invaginations and were densely packed with ribosomes, well-developed rough endoplasmic reticulum, mitochondria, amylopectin granules, lipidic droplets, and wall-forming-like bodies. The latter could participate in the formation of the oocyst wall. Abundant and large mitochondria, together with residual nuclei, appeared in advanced microgamonts. Microgametes showed two flagella with microtubul arranged according to the typical pattern. An increase in polysaccharide content was observed with coccidian development, reaching a maximum in zygotes and unsporulated oocysts.

Ceratomyxa sparusaurati infection was studied in gilthead sea bream from different mariculture systems of Spain. Culture conditions were found to influence the infection dynamics. Total prevalences ranged from 0 in a closed system to 59.9% in a Mediterranean semi-intensive farm. Prevalence was significantly lower in summer in a restricted group from the latter system, but no clear seasonal pattern was observed in the remaining fish groups in any system. A statistically significant dependence between infection prevalence and host weight was observed in some fish groups. Different degrees of histopathological damage were noted in the infected gallbladders, mainly involving swelling, vacuolization, and sloughing of the epithelial cells. Transmission electron microscope observations of the infected tissues demonstrated a characteristic protrusion of the epithelial cell surface and mitochondrial alterations. In fish from stocks showing external disease signs and trickling mortalities, parasite stages invaded other organs and were responsible for cell-mediated host reaction and important tissue injuries. Therefore, C. sparusaurati can be considered a potential threat for some Sparus aurata-growing systems.