Rainbow trout is considered as a most cultivable coldwater exotic species in India. One of the major constrains in rainbow trout farming is infections with oomycetes, saprolegnia species in early stages of life. The losses due to saprolegniasis is around 5-10 % reported by many authors in rainbow trout farms & hatcheries, sometimes these losses are increased upto 50% in many cases. Malachite green is one the most promising antioomycetes agents against pathogenic oomycetes, but because of the carcinogenic & toxic effect it was banned in EU countries in the year 2004. In India, there is no such regulation or law for use of drugs for aquaculture uses. In present study, we have investigated the nine available antioomycetes agents against four isolated saprolegnia sp from different life stages of rainbow trout, & kept malachite green as control. We performed Invitro study to evaluate the efficacy against sporulation, germination and mycelial growth of isolated ooomycetes. In-vivo experiment were also conducted to test the safety of continuous exposure of live eggs, sac fry & fry stages of rainbow trout to different concentration of Boric acid & Formalin. In vitro study suggest, highest minimum inhibitory concentration (MIC) with boric acid, which was found to be 500 ppm for Saprolegnia diclina & 1000 ppm for Saprolegnia parasitica & Saprolegnia australis. Like wise, lowest MIC was observed with chitosan at 10 ppm for Saprolegnia australis & saprolegnia diclina. The high hatchability and safety while in vivo testing of boric acid with eggs may be suggested, safe use within 1000 ppm treatment. While, 10 ppm formalin may be used safely for egg yalk as well as fry stages of rainbow trout. In future, Field trial may be conducted for most promising treatment combination while challenge with different species of saprolegnia in rainbow trout farms and hatcheries.