Inhibition of Saprolegnia pathogenic for fish by Pseudomonas fluorescens

Bacteria capable of inhibiting the growth of Saprolegnia were isolated from commercial channel catfish pond water during January and November 1991. The isolates were typed as Pseudomonas fluorescens with 96% confidence and fluoresced under ultraviolet light. Only three out of the seven otherwise identical subcultures have retained the ability to inhibit Saprolegnia hyphal growth and were positive in gelatin liquefaction assays. Saprolegnia cyst germination inhibition assays indicated that each of the P. fluorescens subcultures inhibited cyst germination at ratios as low as 0.5:1 to 10:1, while Escherichia coli (used as a control) was only inhibitory at a ratio of 500:1. The inhibitory activity against Saprolegnia did not appear to reside in bacterial culture supernatants.