Characterisation of Saprolegnia sp. isolates from channel catfish

Abstract

Nineteen channel catfish isolates of Saprolegnia sp. obtained from 5 separate fish farms in Mississippi, which became affected by winter kill syndrome during 1991 and 1996, were investigated with respect to physiological characteristics and genetic variation. Isolates of S. parasitica from crayfish and S. diclina were included for comparison. Most strains of catfish isolates grew well at 20 and 30°C. Repeated zoospore emergence was found in catfish isolates of Saprolegnia sp. and S. parasitica, but not in S. diclina. Random amplification of polymorphic DNA polymerase chain reaction (RAPD-PCR) was applied for a further characterisation of the isolates. The RAPD analysis among Saprolegnia spp. isolates was constructed from 686 amplified products in 67 separable positions and indicated that the catfish isolates of Saprolegnia sp. are composed of 3 genetically distinct groups.KEY WORDS: Saprolegnia · Saprolegniosis · Fish disease · Random amplification of polymorphic DNA (RAPD) Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [53][54][55][56][57][58][59] 2001 signs of winter saprolegniosis (formerly termed winter kill syndrome). In the case of one fish, isolates were obtained from the eye and fin. All catfish were obtained from catfish farms, at least 50 miles (~80 km) apart, but located within the Mississippi Delta, USA. Isolates obtained in 1991 are designated CF91 and comprise CF91-1 (now deposited in the American Type Culture Collection; ATCC # 200048), CF91-2, CF91-4, CF91-5, CF91-6 and CF91-9. All 1991 isolates were collected from different fish in one pond at Dyche Plantation catfish farm (designated Farm 1, Table 1; Bly et al. 1992, wherein these isolates are referred to as CF1 through CF9). All other isolates collected from catfish were obtained in 1996 and are designated as CF96. CF96-1 through CF96-13 were obtained from different places of origin (see Table 1) in order to determine if geography had an effect on Saprolegnia spp. genetic variation. Four farms were sampled in 1996, TAM-AN (Farm 2), Holly Ridge (Farm 3), Topcat (Farm 4) and Higg (Farm 5). Other strains, i.e. S. parasitica (Spt) isolated from freshwater crayfish Astacus leptodactylus (Söderhäll et al. 1991) and S. diclina (Sdi; ATCC # 42062), were included for comparison. All isolates were maintained on PG-1 agar medium (Unestam 1965).Hyphal radial growth rate. The inoculum was prepared by cutting at the advancing edges of a young colony grown on PG-1 agar with a 6 mm diameter borer. The different Saprolegnia isolates were inoculated on a fresh PG-1 agar dish. The colony hyphal radial growth rates were determined as described by Trinci (1969) at 20 and 30°C. Comparisons of hyphal growth rate between isolates were made using a Student's t-test. Differences were considered significant at p ≤ 0.05.Repeated zoospore emergence. Repeated zoospore emergence was performed according to the method described by Diéguez-Uribeondo et al. (1994). Briefly, mycelia were grown in PG-1 drop cultures ...

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

“…The following reference isolates were used for comparison: S. parasitica (Spt) isolated from freshwater crayfish Astacus leptodactylus (Söderhäll et al 1991), S. parasitica (Spt 198A) isolated from brown trout Salmo trutta (Diéguez-Uribeondo et al 1996), Saprolegnia parasitica (Spt ACTT # 42062/ TP41; formerly named S. diclina Type 3 by Willoughby 1978), Saprolegnia sp. (CF91-1, CF96-2 and CF98-8) isolated from channel catfish (Bly et al 1992, Bangyeekhun et al 2001 and S. diclina (Sdi 2003h). All isolates were maintained on PG-1 agar medium (Unestam 1965).…”

“…Applying the RAPD-PCR technique, Diéguez-Uribeondo et al (1996) demonstrated the spread of a group of closely related strains of Spanish Saprolegnia parasitica isolated from infected trout, and Bangyeekhun et al (2001) showed the presence of 3 genetically distinct groups of catfish isolates of Saprolegnia sp. in Mississippi.…”

“…Even though Saprolegnia sp. could infect many fish species, outbreaks of saprolegniosis are frequently found among salmonid species and their eggs (Hatai & Hoshiai 1992, Noga 1993, Diéguez-Uribeondo et al 1996, Bruno & Wood 1999, Hussein et al 2001) and in farmed channel catfish Ictalurus punctatus (Durborow et al 1991, Bly et al 1992, Bangyeekhun et al 2001.…”

“…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.…”

Morphological and molecular phylogenetic analysis of two Saprolegnia sp. (Oomycetes) isolated from silver crucian carp and zebra fish

“…Random amplification of polymorphic DNA polymerase chain reaction (RAPD-PCR) has also been applied to the analysis different species and isolates of fish pathogenic Saprolegnia spp. (Dié guez-Uribeondo et al 1996;Bangyeekhun et al 2001). This method is fast and economic for screening large numbers of samples and can offer the possibility of detecting polymorphisms without any prior knowledge of the DNA sequences of the organism investigated.…”