Characterisation of Saprolegnia sp isolates from channel catfish

Nineteen channel catfish isolates of Saprolegnia sp, obtained from 5 separa te fish farms in Mississippi, which became affected by winter kill syndrome during 1991 and 1996, were investigated with respect to physiological char acteristics and genetic variation. Isolates of S. parasitica from crayfish and S. diclina were included for comparison. Most strains of catfish isolat es grew well at 20 and 30 degreesC. Repeated zoospore emergence was found i n catfish isolates of Saprolegnia sp. and S, parasitica, but not in S. dicl ina. Random amplification of polymorphic DNA polymerase chain reaction (RAP D-PCR) was applied for a further characterisation of the isolates. The RAPD analysis among Saprolegnia spp, isolates was constructed from 686 amplifie d products in 67 separable positions and indicated that the catfish isolate s of Saprolegnia sp. are composed of 3 genetically distinct groups.