Kemampuan Bakteri Antagonistik dalam Menghambat Infeksi Saprolegnia Sp. pada Ikan Nila (Oreochromis Niloticus)

Abstract

Fish diseases like saprolegniosis cause big economic loss in aquaculture especially tilapia. The study about ability of antagonistic bacteria to inhibit infection of Saprolegnia sp. in tilapia (Oreochromis niloticus) has been done in the Laboratory of Microbiology, Bureau of First Class Fish Quarantine Polonia and Laboratory of Microbiology, Department of Biology, Faculty of Mathematics and Sciences, University of North Sumatra, Medan. Three isolates of water mold [Saprolegnia sp., Aphanomyes sp. and not yet identified isolate (L01)] were isolated from infection of catfish eggs and tilapia. Test of pathogenicity indicated that Saprolegnia sp. was most pathogenic, with 90% death and infection and was used for further test. Antagonism test in vitro showed that three antagonistic bacterial isolate (Enterobacter sp. PB17, Bacillus sp. BK17 and PB08) had ability to inhibit of water mold with diameter of inhibition zone 8,50 mm, 8,04 mm and 7,55 mm. Enterobacter sp. PB17 isolate had ability better than other antagonistic bacteria isolate to inhibit all of water mold isolate. However test of controlling saprolegniosis in tilapia indicated that isolate Bacillus sp. BK17 and Enterobaceter sp. PB17 most to inhibit infection of Saprolegnia sp. with amount of healthy fish had seen until end of day seupervision respectively percentage 86% and 84%. Observation using scanning electron microscope of fish skin showed that the bacterial isolate might attach to the fish so that might press infection of pathogen in tilapia.