Macroscopic and histopathological changes in cultured turbot, Scophthalmus maximus (L.), in Spain caused by infection with Edwardsiella tarda are described. Eye tumefaction, inflammation, haemorrhages, ascites and the presence of a purulent fluid were the main macroscopic lesions observed. Histopathological lesions were found in the kidney, spleen and liver. In the kidney and spleen these were characterized by a severe apostematous inflammatory reaction, with a large number of abscesses. The liver was affected to a lesser degree and only some phagocytes loaded with bacteria were observed. Ultrastructural observations indicated that macrophages were the main cell type implicated in the inflammatory response. Most of the bacteria observed within the phagocyte cytoplasm showed no degenerative changes and some were dividing. Degenerative changes observed in macrophages indicate their failure in preventing the infection.

Elongate plasmodia with myxosporean spores belonging to the genus Unicapsula, Davis, 1924 were found in the skeletal muscle of the striped seabream, Lithognathus mormyrus (L.), a candidate for the mediterranean aquaculture. The only species of Unicapsula described from the Mediterranean is Unicapsula pflugfelderi Schubert et al. 1975, which occurs in the picarel, Spicara smaris (L.). For morphological and molecular comparison of U. pflugfelderi from S. smaris with Unicapsula sp. from L. mormyrus measurements of plasmodia and spores, ultrastructural details and 18S and 28S rDNA sequences were analysed. Whereas plasmodia were 2-3 times larger in S. smaris than in L. mormyrus (length 2.47-0.81 mm; width 0.22-0.09 mm; P = 0.000), spore morphology showed minor differences and both 18S and 28S rDNA sequences were 100% identical identifying the myxozoan as U. pflugfelderi. Scanning electron microscopy of the spores revealed a different shell valve distribution than the one used for the diagnosis of the genus Unicapsula. This resulted in a review of the genus Unicapsula dividing it into two morphological groups of different spore valve arrangement. TEM revealed the presence of a yet undescribed crystalline structure in the sporoplasm of the spores.

In the course of experimental infections of gilthead sea bream Sparus aurata with the myxozoan Enteromyxum leei, stages of an unidentified myxozoan were observed attached to the intestinal brush border of some fish. Infection levels of the parasite, which was named "epi-epithelial myxosporean" (EEM) were recorded, and its structure was studied by light microscopy (LM) and electron microscopy (EM). In situ hybridisation (ISH) probes specific for E. leei were developed and used to differentiate between the two parasites. The EEM parasite was observed only in epi-epithelial position on the intestine mucosa and never in any of the other tissues studied (kidney and gall bladder). Prevalence was variable, with values reaching 40.2%. With transmission EM, trophozoites displayed pseudopodia-like projections inserted in between the enterocyte microvilli, producing an intimate interface. No mucosal histopathology that could be attributed to the myxozoan was found. EEM stages did not stain with the E. leei-specific ISH probes. From the results of the LM, EM and ISH studies, we conclude that the EEM parasite found in gilthead sea bream intestine in both Mediterranean and Red Sea sites is a coelozoic myxosporean, distinct from E. leei.

The ultrastructure of the developmental stages of the myxozoan Enteromyxum leei parasitizing gilthead seabream (Sparus aurata) intestine and sharpsnout sea bream (Diplodus puntazzo) intestine and gallbladder are described. The earliest stage observed was a small dense trophozoite located among enterocytes. Proliferative stages, observed intercellularly in the epithelium of the intestine and gallbladder as well as in the lumen, possessed the typical cell-in-cell configuration throughout their development. Secondary cells were seen undergoing division within a common vacuolar membrane that also encompassed pairs of tertiary cells. Cytochemical studies showed that primary cells stored mainly lipids whereas secondary cells stored abundant beta-glycogen granules. Sporogonic development resembled that described for other disporous myxozoans. Within sporogonic stages, nonsporogonic secondary cells were observed accompanying two developing spores. Mature spores had a binucleated sporoplasm in which glycogen stores were abundant and no sporoplasmosomes were found. Our observations are discussed in relation to our knowledge on other myxozoans of the genus Enteromyxum.