Efficiency of Syzygium aromaticum and Punica granatum extracts for the prevention of saprolegniasis on Oreochromis niloticus fish

Saprolegniasis is considered as one of the most problematic fish diseases, causing high mortality and significant economic losses in fish farms especially Oreochromis niloticus hatcheries. Chemotherapeutic treatment of fungal fish diseases with chemicals and malachite green was proved to possess carcinogenic and teratogenic effects in fish and human health. Hence, the current study aimed to investigate antifungal activities of three plant extracts against the causative agent of saprolegniasis, Saprolegnia parasitica, as an alternative fungicides. Disc diffusion assay was conducted for the preliminary antifungal bioassay of the most effective plant extracts. Acute fish toxicity and phytochemical analysis of the functional plant extracts were performed to ensure their safety for application and detect their phytoactive components. Ethanolic extracts of Syzygium aromaticum and Punica granatum showed a potential efficiency in preventing mycelial growth of S. parasitica at a concentration of 0.5 mg/ml recording inhibition zone diameters of 18.35 and 16.5 mm respectively. The clove extract exhibited the highest anti-sparolegnial potency recording minimum inhibitory concentration (MIC) of 100 ppm, which was significantly higher than that of concentration 50 ppm at p ≤ 0.05. Acute fish toxicity of the potential plant extracts revealed that both P. granatum and S. aromaticum exhibited low toxicity to experimental fish, O. niloticus, recording LC50 ranging from 1600 to 1330 ppm and no mortalities were recorded even at 400 ppm. Regarding their low toxicity, it can be suggested that the effective concentrations of clove and pomegranate extracts could be considered as a safe, eco-friendly and applicable measure for saprolegniasis control.