Use of Thyme and Thymol as Immunostimulant Agents to control Experimental ‎Aeromonas hydrophyla Infection in Nile Tilapia (Oreochromis niloticus)‎

In the current investigation, a total of 110 Oreochromis niloticus were collected from aquaculture farm at Sahl Eltina area, North Sinai Governorate suffering from skin and fin ulcers with ascites, exophthalmia, and high mortalities. Aeromonas hydrophyla was isolated with a prevalence rate of 40% and identified biochemically. A . hydrophyla was used to induce experimental infection to Nile Tilapia in which thyme and thymol were used as feed additive. Evaluation of the protective effect of thyme and thymol as immunostimulant agents on fish tissue against experimental infection with Aeromonas infection was studied. A total of ninety apparently healthy fish tilapia were divided into three groups (GA, GB and GC of 30 fish per group) in triplicate. GA (infected non treated group) was fed on basal diet. GB and GC were fed on diet supplemented with Thyme vulgaris (10 g/ kg diet) and Thymol (3 g/ kg diet), respectively for 8 weeks and then the groups were subjected to experimental infection with Aeromonas hydrophyla isolate. The thyme and thymol groups had a nearly similar significant immunostimulant effect than infected non treated group by using lysozyme activity assay. Sever hyperemia of gill filaments and gill arch, epithelial desquamation of the gill filament, enteritis, necrosis and desquamation of epithelial cells of intestine, muscle necrosis, myocardiolysis of heart, hydropic degeneration of liver and hemosiderosis of spleen were observed in infected non treated group. In the treated groups, the prophylactic effect of thyme and thymol on fish tissues were clear against experimental infection with A. hydrophyla . These results indicate that the using thyme or thymol as feed additive could enhance the immunity and protect fish tissues from pathological deterioration induced by infection with Aeromonas hydrophila which is considered as one the main fish pathogens in Egypt.