The use of Ocimum americanum essential oil against the pathogens Aeromonas hydrophila and Gyrodactylus sp in silver catfish (Rhamdia quelen)

The bactericidal activity (minimum inhibitory concentration (MIC)-test) of Ocimum americanum (inflorescences) essential oil (OAEO) against Aeromonas hydrophila was determined in this study. Also investigated was the potential of OAEO and the main compound found in the oil (linalool) at subinhibitory concentrations to be inhibitors of haemolysis caused by Aer.hydrophila in fish erythrocytes. An invivo experiment was conducted to evaluate the survival of fish (Rhamdia quelen) experimentally infected with Aer.hydrophila and exposed to OAEO. A second experiment was conducted to evaluate the invitro and invivo activity of OAEO (mix from inflorescences and leaves) against the parasite Gyrodactylus sp. The OAEO showed weak invitro activity against Aer.hydrophila (6400gml(-1)). Subinhibitory concentrations of OAEO (100gml(-1)) inhibited haemolysis (90%) caused by Aer.hydrophila in fish erythrocytes, however, linalool did not inhibit haemolysis activity. At the low concentrations (10 and 20mgl(-1)) added to the water, OAEO promoted the survival of fish experimentally infected with Aer.hydrophila. Lastly, the OAEO mix (50mgl(-1)) was effective against Gyrodactylus sp., significantly reducing (60%) the number of parasites in the fish.