A Study of Potential Control of Watermold Saprolegnia Sp. of Gouramy (Osphonemus gouramy) Eggs by Bacterial Isolates

A study on potential biological control of 10 bacterial isolates isolated from healthy gouramy pond to inhibit the Saprolegnia sp. causal agent of saprolegniasis in gouramy egg was carried out. The ability of bacterial isolates to inhibit Saprolegnia sp. was evaluated in vitro by antagonistic assay on minimum salt medium agar with 2% colloidal chitin as C source, and conducted in vivo by examining all isolates to reduce saprolegniasis in gouramy egg. Hyphal abnormality as a result of antagonistic assay was examined. Adherence test of bacterial isolate cells to egg surface was performed. The result showed that all isolates, except that of PB08 and PB10 indicated to produce chitinase and other antifungal substances. All bacterial isolates showed to inhibit growth of the fungi except that of PB01 which was pathogen to gouramy eggs. Microscopic observation showed that hyphal necrosis was a common abnormality found, followed by hyphal tip necrosis, bent hyphae, and broken hyphae, respectively after antagonistic assay. All bacterial isolates were attached on the egg surface, except that of PB17 which was loosely attached on the egg surface. This study indicated that PB05, PB08, PB13, PB14, and PB15 could be used as potential biological control candidates against saprolegniasis.