Histophagous scuticociliatids (Ciliophora) parasitizing turbot Scophthalmus maximus: morphology, in vitro culture and virulence

Abstract

Abstract. Systemic ciliatosis caused by histophagous ciliates constitutes a serious disease of cultured turbot. Six ciliate isolates were obtained from parasitized turbot during six epizootics at four different farms located in Spain, France and Portugal. Axenic cultures of the six isolates were obtained by periodical subculturing in ATCC 1651MA or supplemented L-15 media. In basal media or seawater, the parasites could survive starving for long periods with no apparent proliferation. In adequate media, growth kinetics was found to be very similar for isolates A and B, with a clear influence of temperature. Morphological studies demonstrated that all isolates share common features that allows their assignment to either Philasterides Kahl, 1931 or Miamiensis Thompson et Moewus, 1964. However, statistically significant differences were evident in pairwise comparisons of the isolates from the four farm sites in 16 taxonomically relevant morphometric features. This could allow the discrimination of different species or strains. Virulence of isolates A and B for healthy turbot was tested in several experiments. Differences in the virulence were especially evident after long-term in vitro culturing, isolate A being clearly attenuated after 35-42 passages, whereas isolate B became more virulent after 20-42 passages. The need of further studies to confirm such virulence variability and its implications in pathogenesis and prevention of turbot scuticociliatoses is stressed.Scuticociliates are ciliate protozoans (Ciliophora) occurring abundantly in eutrophic coastal and saprobic maricultural waters. Some of them can behave as opportunistic histophagous parasites causing severe infections in crustaceans and fish. Small (1967) proposed the new order Scuticociliatida including the suborders Pleuronematina, Pseudocohnilembina and Philasterina. Further revisions of the Ciliophora (Lynn and Small 2000) granted scuticociliates the level of subclass (Scuticociliatia), and the suborder Philasterina was ranked as order (Philasterida). Since the criteria used hitherto to classify the families, genera and species of scuticociliates have been variable, the taxonomy of these organisms is currently rather confusing.Recently, different scuticociliates have become an important threat for cultured marine fish such as tuna and different flatfish. Fatal encephalitis of bluefin tuna, attributed to Uronema nigricans, was reported by Munday et al. (1997). Among flatfish, Jee et al. (2001) described scuticociliatosis of Japanese flounder, Paralichthys olivaceus. In turbot, different episodes of scuticociliatosis have been reported in Spain (Dyková and Figueras 1994, Iglesias et al. 2001, authors' unpublished data) and Norway (Sterud et al. 2000). Only in one of these turbot epizootics the causative organism was identified to specific level as Philasterides dicentrarchi Dragesco, Dragesco, Coste, Gasc, Romestand, Raymond et Bouix, 1995by Iglesias et al. (2001. This species was originally described from an episode of Mediterranean seabass (Dice...

Identification of scuticociliate Philasterides dicentrarchi from indo-pacific seahorses Hippocampus kuda

“…The causative agents of scuticociliatosis in Korea have been isolated and identified as Uronema marinum (Jee et al, 2001), Pseudocohnilembus persalinus (Kim et al, 2004b), Philasterides dicentrarchi (Kim et al, 2004a). P. dicentrachi and Miamiensis avidus have caused mass mortality in turbot farms in Spain, Portugal, and France (Dyková and Figueras, 1994;Iglesias et al, 2001;Álvarez-Pellitero et al, 2004;Paramá et al, 2004). Seahorses are especially popular in some Asian countries due to strong demand from the Chinese traditional medicine and the souvenir trade on a global scale (Marichamy et al, 1993;Vincent, 1995).…”

Pathological Study on the Scuticociliatosis Affecting Farmed Japanese Flounder (Paralichthys olivaceus) in Japan

“…Scuticociliates are free-living in sea-water, and typically scavengers that feed on suspended particulate matters but, under certain circumstances, these ciliates may behave as opportunistic histophagous parasites and actively feed on cells of certain mollusks, crustaceans and fishes, and continue to live and reproduce within the host tissues [1]. Infections by histophagous scuticociliates (scuticociliatosis) have become one of the most important worldwide parasitological diseases in the intensive marine culture of flatfish species including Japanese flounder (Paralichthys olivaceus) [6].…”

Ocurrencia de escuticociliatosis en el lenguado Paralichthys adspersus causado por Miamiensis avidus, en Perú

“…Probablemente algunas enzimas o alguna toxina de M. avidus destruyen la piel y músculo de P. adspersus, ocasionando úlceras y necrosis y posteriormente ganan entrada a los órganos internos por las microlesiones producidas y por vía sanguínea (Jin et al 2009), tal como se ha hipotetizado (Paraná et al 2003, Azad et al 2007. Alvarez-Pellitero et al (2004) reportaron que la infección experimental por inmersión con P. dicentrarchi sólo fue eficaz después de la abrasión de branquias y piel, ya que en centros de cultivo, los parásitos pueden sobrevivir en el fondo de los tanques ricos en nutrientes, y llegar a ser significativamente patogénicos solo cuando los peces desarrollan lesiones superficiales (Jin et al 2009) Por otro lado, el cerebro fue el órgano más parasitado y además, fue el que se encontró infectado sin que otros órganos lo estén en el mismo ejemplar muestreado. Es importante resaltar que los peces en los que se encontraron ciliados en el cerebro generalmente no presentaron abultamiento de la cavidad visceral y los órganos internos estuvieron levemente parasitados o no parasitados.…”