Anti-saprolegnia potency of some plant extracts against the causative agent of saprolengiasis.

Saprolegnosis of fresh water fishes caused by often results in serious economic losses to fish hatcheries. Despite the proven efficiency of malachite green as a potential fungicide in prevention and control of fish saprolegnosis, there is a strong debate about its safety aspects in use since it was documented to be responsible for many carcinogenic and teratogenic attributes. Bioactivity of four ethanolic plant extracts were assessed to attain a natural alternative to the traditional fungicide currently used in saprolegnosis control. Ethanolic extracts of and exhibited a potential efficacy in suppressing mycelial growth of at concentration of 0.5 mg/ml while extracts of and were not effective respectively. The extract of pomegranate showed the highest antifungal potency with minimum inhibitory concentration (MIC) of 200 ppm while thyme extract was less effective and recorded MIC of 400 ppm against . The acute fish toxicity of the plant extracts indicated the low toxicity of and extracts as no fish mortalities were detected at aquaria containing 200, 400 and 800 ppm of plant extracts respectively. Considering the low toxicity of these plant extracts, it may be concluded that 200 and 400 ppm of pomegranate and thyme extracts which suppressed the mycelial growth of the S. could be safely used for saprolegniasis control. Both of pomegranate and thyme extracts which proved to possess a potential antifungal activity can be considered as a natural alternative fungicides to control saprolegniasis avoiding carcinogenic malachite green application.