Prevalence of a single fish-pathogenic Saprolegnia sp. clone in Finland and Sweden

Abstract

Thirty-one isolates of Saprolegnia sp., most originating from infected salmon or trout, were characterised genetically and physiologically. The majority (6 of 31) of the isolates from several widely separated geographical locations was found to be genetically almost identical as assessed by RAPD-PCR. The remaining isolates belonged to 3 different groups with 1 to 3 representatives each. It is suggested that the first group of isolates represents a virulent form of the organism that has been widely spread by clonal propagation. The ability to repeated zoospore emergence, as an alternative to direct germination, seems to characterise specific Saprolegnia genotypes that may have adapted to certain hosts.KEY WORDS: Saprolegnia · Saprolegniosis · Fish disease · Random amplification of polymorphic DNA RAPD · Repeated zoospore emergence Resale or republication not permitted without written consent of the publisherDis Aquat Org 53: [47][48][49][50][51][52][53] 2003 guished the fish lesion isolates from the water isolates, and Beakes (1983) was able to identify S. parasitica from S. diclina. Variation in esterase isoenzyme patterns (Beakes & Ford 1983) and differences in radial growth rate (Willoughby & Copland 1984, Hatai et al. 1990) have been used for determining distinct groups of fish lesion isolates. Restriction fragment length polymorphisms (RFLPs) are useful for classification of Saprolegnia and could distinguish S. parasitica from S. diclina (Molina et al. 1995). Also, random amplification of polymorphic DNA polymerase chain reaction (RAPD-PCR;Welsh & McClelland 1990, Williams et al. 1990) has been applied for analysis of the fish pathogenic Saprolegnia genome (Diéguez-Uribeondo et al. 1996, Bangyeekhun et al. 2001). This latter method provides a sensitive and rapid assay for the assessment of genetic distance between different isolates.In the present study, we applied the RAPD-PCR technique and the presence or absence of repeated zoospore emergence to characterise Saprolegnia sp. isolates obtained from Finland and Sweden to investigate the epidemiology of the saprolegniosis in this region. We found that the majority of the isolates belonged to a single genetically defined group that probably has been widely spread by clonal propagation. MATERIALS AND METHODSSaprolegnia strains. Thirty-one isolates of Saprolegnia spp. were isolated from infected tissue of the brown trout Salmo trutta m. lacustris, trout S. trutta, whitefish Coregonus lavaretus, rainbow trout Oncorhynchus mykiss, brook trout Salvelinus fontinalis, landlocked salmon Salmo salar m. sebago, salmon S. salar, noble crayfish Astacus astacus, and pond water from 6 different locations in Finland and 1 location in Sweden. The isolates from Finland are designated FinX, where X is the isolation number and the isolates from Sweden are designated Swe203 and Swe239 (see Table 1). The following reference isolates were used for comparison: S. parasitica (Spt) isolated from freshwater crayfish Astacus leptodactylus (Söderhäll et al. 1991), S. parasit...

Re-evaluation of the enigmatic species complex Saprolegnia diclina–Saprolegnia parasitica based on morphological, physiological and molecular data

“…This may suggest that this low variation is the consequence of a clonal propagation of animal parasitic Saprolegniaceae. Evidences for such clonal propagation were reported in A. astaci (Huang et al, 1994;Dié-guez-Uribeondo et al, 1995), A. invadans (Lilley et al, 2003) and S. parasitica (Diéguez-Uribeondo et al, 1996;Bangyeekhun et al, 2003). Clonal propagation may favor exploitation of a pathogenic character .…”

Saprolegnia diclina: another species responsible for the emergent disease ‘Saprolegniainfections’ in amphibians

“…This ability may increase the likelihood that the pathogenic strain will find an appropriate substratum to germinate, e.g. amphibian eggs, thus ensuring their survival, as proposed for Saprolegnia strains isolated from salmonids in Finland (Bangyeekhun et al , 2003). The presence of this character should be investigated in other strains involved in embryonic die‐offs of amphibians to determine whether it may constitute a virulence factor, and whether or not other highly pathogenic strains or species of Saprolegnia may be present in the environment.…”

Differences in susceptibility to Saprolegnia infections among embryonic stages of two anuran species

“…These zoospores are biflagellate and quickly encyst to form primary cysts that can germinate or release a new generation of zoospores (Diéguez-Uribeondo et al 1994Fernández-Benéitez et al 2008;Ke et al 2009;Ghiasi et al 2010). This ability may increase the likelihood of finding an appropriate substratum to germinate and thus ensuring survival (Bangyeekhun et al 2003).…”