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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.

Following the first report and description of Myxidium leei in cultured gilthead sea bream, Sparus aurata L., from southern Cyprus (Diamant, Lom & Dyková 1994), the parasite was ascribed to the genus Enteromyxum (Palenzuela, Redondo & Alvarez-Pellitero 2002) and the list of susceptible host species has since expanded to more than 45 with a parallel geographical spread (Diamant 1995, 1998; Le Breton & Marques 1995; Sakiti, Tarer, Jacquemin & Marques 1996; Paperna 1998; Zrnčić, Oraić, Šoštarić & Fillić 1998; Padrós, Palenzuela, Hispano, Tosas, Zarza, Crespo & Alvarez-Pellitero 2001; Marino, Macri, Paruta, Busalacchi, Genovese & De Vico 2004; Yanagida, Nomura, Kimura, Fukuda, Yokoyama & Ogawa 2004; Yasuda, Ooyama, Nakamura, Iwata, Palenzuela & Yokoyama 2005; Diamant, Ram & Paperna 2006; Yanagida, Palenzuela, Hirae, Yokoyama & Ogawa, unpublished data). In spite of the impact of this enteric parasite in gilthead sea bream and sharpsnout sea bream, Diplodus puntazzo (Cetti), culture (Athanassopoulou, Prapas & Rodger 1999; Rigos, Christophilogiannis, Yiagnisi, Andriopoulou, Koutsodimou, Nengas & Alexis 1999; Ghittino, Latini, Agnetti, Panzieri, Lauro, Ciappelloni & Petracca 2003; Golomazou, Karagouni & Athanassopoulou 2004; Merella, Cherchi, Salati & Garippa 2005; Oraić & Zrnčić 2005; Palenzuela 2006), relatively little is known about its transmission and infection routes, and the primary host species in the wild remains unknown.

Traditionally, the most common approach to diagnosis of microbial fish pathogens has relied on in vitro isolation of the microorganism and the information provided by its phenotypic features. However, viruses are generally highly species-specific and established cell lines do not neces- sarily show cytopathic effect, many species of bacteria are difficult or impossible to culture in vitro, while parasitic microorganisms often have a complex life cycle that requires propagation in live hosts. An increasing number of microbial pathogens are identified today by molecular meth- ods, without the need for isolation. A PCR direct method for detection and identification of Mycobacterium marinum based on the 16S rRNA gene sequence was successfully developed already 13 years ago at NCM. Comparison of the 16S rRNA sequence of Streptococcus iniae isolates revealed that, despite phenotypic, biochemical and pathogenetic similarities, marine and freshwater isolates were different strains. With time, however, it has become clear that 16S rRNA gene sequences alone are often insufficient to detect variation within bacterial species, and today other specific loci are also being employed. More recently, on the basis of hsp65 gene in addition to 16S rRNA gene, Israeli M. marinum isolates in marine and freshwater fish were found to belong to two distinct strains, and both were different from Israeli M. marinum clinical (human) isolates. Specific 18S rDNA probes for detection of elusive life stages of two myx- osporean parasites, Kudoa iwatai and Enteromyxum leei, in sea bream and sea bass are being employed in studies conducted over the last few years at NCM. By using whole-genome struc- tures rather than single gene sequences, two fingerprinting techniques - Amplified Fragment Length Polymorphism (AFLP) and Randomly Amplified Polymorphic DNA (RAPD) - have pro- vided a generally higher level of precision in genotyping. However, while the AFLP method revealed broad polymorphism among S. i

A case of mycobacteriosis in European sea bass (Dicentrarchus labrax L.) cultured in Turkey is described. Diseased fish were characterized by lethargy, lingering passively at the water sur- face, pale gills, and exophthalmia. Internally, grayish-white nodules were observed in the liver, spleen, and kidney. In one individual, a granulomatous mass of renal origin protruded into the abdominal cavity. The principal histological feature was the occurrence of characteristic granu- lomas with associated acid-fast, rod-shaped bacteria. This is the first confirmed case of fish mycobacteriosis in Turkey.

Since spring 1998, a new disease causing high mortality has afflicted cultured ornamental and common carps (Cyprinus carpio) in Israel. The clinical signs of the disease are fatigue, gasping movements in shallow water, gill necrosis, sunken eyes, pale patches on the skin and increased mucus secretion. The disease was experimentally transmitted to koi and common carp of vari- ous ages by injection with affected tissue filtrates, cohabitation trials and exposure to the isolat- edviralagent.Immersionofhealthyfishintankscontaining2.7x104 plaqueformingunits(PFU) per l or intraperitoneal injection (0.2 ml) of a viral inoculum of 1000 PFU/ml were sufficient to induce the terminal disease in over 80% of the fish. Here we report that the disease is restrict- ed to C. carpio, that young fish of 2.5 g and 6 g are more sensitive to the virus than adults (230 g) and that the virus remains active in the water for at least four hours.