Yersinia ruckeri, the causal agent of enteric redmouth (ERM) disease, was isolated from epizootics that occurred in different Spanish rainbow trout, Oncorhynchus mykiss (Walbaum), farms in which vaccination against ERM had been performed. In all episodes, the most pronounced clinical signs exhibited by affected fish were severe haemorrhages in the mouth, eyes and around the vent. The isolates were identified as Y. ruckeri serovar I by 16S rRNA sequencing together with serological tests. They lacked motility and lipase activity and thus belonged to biotype 2, and were highly virulent for juvenile rainbow trout, both by intraperitoneal injection (from 3.1 x 10(2) to 6.3 x 10(3) cfu per fish) and bath challenge (5.1-7.3 x 10(6) cfu mL(-1)). This is the first description of Y. ruckeri serovar I biotype 2 causing disease in cultured trout in Spain vaccinated with commercial ERM vaccines. The occurrence of this emergent pathogen in Spanish continental aquaculture from its first isolation in 2001 to date is also documented.

The morphology of membrane-bound intracellular inclusions, or 'cysts', of epitheliocystis from sea bream Sparus aurata is described. Inclusions under the light microscope appear either granular or amorphous. Granular inclusions do not elicit a proliferative host reaction and contain the 3 distinctive developmental stages of chlamydial organisms: the highly pleomorphic reproductive form or reticulate body, the condensing form or intermediate body and the infective non-dividing rather uniform elementary body. Amorphous inclusions may elicit a proliferative host reaction and contain prokaryotic organisms which differ morphologically from those reported within granular cysts. More or less elongated electron-lucent organisms divide by fission to give rise to electron-dense non-dividing small cells with a dense nucleoid. Vacuolated and non-vacuolated small cells are reported. The morphology and developmental cycle of sea bream epitheliocystis agents would support their chlamydial nature; however, the imn~unohistochen~ical study conducted on gill samples which carried both inclusions failed to demonstrate the expression of lipopolysaccharide (LPS) chlamydial antigen. The different stages of the 2 distinct developmental cycles described in the present study are compared with electron microscope observations of epitheliocystis organisms reported from different host species. The hypothesis that epitheliocystis infection in the sea bream might be caused by a unique highly pleomorphic chlamydia-like agent, the life history of which includes 2 entirely different developmental cycles, is discussed.

An episode of parasitic enteritis causing trickling mortalities at an exhibition aquarium reproducing Mediterranean ecosystems was found to be caused by the myxozoan parasite Myxidium leei Diamant, Lom & Dykova 1994. The myxozoan was recorded in 25 different fish species belonging to 16 Genera, 10 Families and 4 Orders. It was mainly detected in the intestine of affected fish, and was responsible for severe chronic enteritis. The parasite was probably introduced into the facilities with infected wild fish, and transmitted directly from fish to fish by cohabitation, transfer of infected material and necrophagia. Fish belonging to the Families Labridae and Blenniidae appeared as most susceptible, and the incidence of infections in members of the Sparidae was low. This study significantly widens the host spectrum for this virulent parasite and now includes many ubiquitous coastal Mediterranean species. Wild fish may have a significant role in the transmission of myxidiosis of cultured sparid fish. KEY WORDS: Myxidium leei · Mediterranean fish · Aquaria · Infection Resale or republication not permitted without written consent of the publisherDis Aquat Org 47: [57][58][59][60][61][62] 2001 MATERIALS AND METHODSFrom January 1999 to June 2000, trickling mortalities affecting different fish species were noticed at several exhibition tanks of 'L'Aquàrium', Barcelona, Spain. This large recreational aquarium maintains 2 systems, 'Mediterranean' and 'Tropical', which receive completely independent water supplies. The Mediterranean system facilities include several 5 to 90 m 3 tanks reproducing different Mediterranean coastal ecosystems, quarantine and stock tanks, and a large 3700 m 3 'Oceanarium'. Fish from this system are held in seawater (39 ‰ salinity, 18 to 19°C), with common filtration equipment, and fed a mixture of commercial food, whole sardine, mackerel, blue whiting, mussel, shrimp, squid and spinach. Effluent water from exhibition and quarantine facilities is actively disinfected with ozone treatment (redox: 700 mV).All the specimens studied were captured from the wild (NE Spanish Mediterranean Coast). After a variable quarantine period (2 wk minimum) the fish were introduced into the exhibition tanks. Once in the exhibition facilities, fish were occasionally moved between tanks according to the program requirements. In most cases this fact and the lack of individual identification did not allow us to know the time of residence of each affected fish in the facilities.Affected fish were removed from the aquaria and necropsies were carried out immediately. Scrapings of the intestinal mucosa were obtained and observed under the light microscope. When the presence of myxozoan spores was confirmed, samples of different levels of the digestive tract were fixed in 10% phosphate buffered formalin for histopathological studies and preserved in 70% ethanol for parasitological examination. Samples for histopathological studies were serially dehydrated and embedded in paraffin using standard procedures. Histol...

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.

Infections with betanodavirus affect a wide range of wild and farmed fish species throughout the world, mostly from the marine environment. The aim of this work was to develop and validate real-time RT-PCR assays for sensitive and specific detection of nodavirus in diseased or carrier fish. The new detection assay was used to study the transmission and development of nodavirus infection in juvenile sea bass, Dicentrarchus labrax (L.), challenged by different routes, and also to screen for nodavirus in various farmed fish species. On average, the sensitivity was 10-100 times higher than a standard RT-PCR, and the assay was able to detect asymptomatic carrier fish that otherwise could have been classified as free of infection. Clinical signs of nodavirus infection were reproduced in fish infected following bath exposure or intramuscular injection, demonstrating horizontal transmission of the disease. Nodavirus was always detected in the brain of diseased fish but also in many recovered fish. The new assay enables us to confirm the presence of the virus at an early phase in the production cycle and may represent a useful tool to prevent or slow down the spread of nodavirus to new locations.