Characterisation of Saprolegnia sp. isolates from channel catfish.

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 degrees 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.