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A scuticociliate strain (B-2), originally isolated from an outbreak in a turbot Scophthalmus maximus (= Psetta maxima) farm in Galicia (northwestern Spain) and maintained in axenic culture, was injected intracoelomically (lethal dose 80 equivalent, LD80) in healthy turbot (50 g). Ciliate-injected fish were kept under controlled conditions in a recirculating seawater system and sampled on Days 1 through 8, 10, 12 and 14 postinfection (PI). Necropsies were conducted and included blood collection from the caudal vein and samples of liver, spleen, heart, digestive tract, kidney, gills, abdominal wall and neurocranium taken for routine histology. Mortality occurred from Day 6 until Day 12 PI and reached 66.7% by the end of the experiment. Presence of ciliates in the coelomic fluid was scarce until Day 4 PI. Parasitaemia was only observed from Day 5 until Day 10 PI and its incidence was always low. Presence of scuticociliates in tissue sections followed a progressive pattern of diffusion, with ciliates showing preference for loose connective tissue and also a clear haematophagous activity. The most severely affected organs were the pancreas and digestive tract. No special tropism for nervous tissues was observed in this study. The inflammatory reaction was variable depending on the tissue. After 3 wk, survivors had apparently managed to extinguish the infection.

Two outbreaks of scuticociliatosis affecting farmed turbot Scophthalmus maximus in Galicia are described. Moribund fish showed cutaneous ulcers, darkened skin, swimming behaviour alterations, exophthalmos, and/or abdominal distension as a result of accumulation of ascitic fluid in the body cavity. Ciliates were detected in fresh mounts of practically all organs and tissues, including the blood and ascitic fluid. Histopathological studies revealed severe encephalitis and meningitis (associated with different degrees of softening or liquefaction of the brain), necrosis of the hepatic parenchyme, severe oedema of the intestinal wall, degeneration of muscle fibres, hyperplasia of the branchial epithelium, and/or vascular and perivascular inflammation. In some cases, parasites are surrounded by abundant monocytic and lymphocytic infiltrate. We report the morphological and biometric characteristics of this ciliate, which allow identification as Philasterides dicentrarchi. We discuss possible routes of entry into the host, and environmental factors possibly facilitating infection.