Therapeutic and histopathological effect of Aloe vera and Salvia officinalis hydroethanolic extracts against Streptococcus iniae in rainbow trout

Some of medicinal plants have antibacterial content and appear to be proper alternative for antibiotics in the treatment of streptococcal disease, which causes many mortality in fish farms annually. Therefor in this study therapeutic effect of Aloe vera and Salvia officinalis hydroethanolic extracts against Streptococcus iniae in rainbow trout was investigated. Plant extracts components were analyzed by GC/MS method and tested in vitro against S. iniae by disk diffusion assay. In in vivo, 480 rainbow trout (10 ± 0.1 g) were distributed in 9 groups (with 3 replication), and all fish of groups (except the first group as negative control, injected with 100 µl of physiologic serum) were injected by 100 µl of LD50 (3.66×108.5 CFU/ml) of S. iniae suspension, interaperitonally. The fish of groups were treated by A. vera and S. officinalis extracts in doses 0 (positive control group were fed by commercial diet without plant extract), 0.5, 1 and 1.5% (supplemented diet) and 80 mg/kg body weight erythromycin for next 10 days. At the end of study period, tissues samples of gills and liver of all groups were taken to assay histopathological lesions. The results showed A. vera and S. officinalis had antibacterial components as Cineol, and S. iniae was sensitive to both A. vera (MBC=4.067 mg/ml) and S. officinalis (MBC=5.185 mg/ml) extracts. At the end of treating period, In case of mortality of infected fishes, erythromycin, A. vera (1.5%) and A. vera (1%) exhibited no significant (P˂0.05) difference together. A. vera (1.5%) was shown lower mortality in compare positive control significantly (P˂0.05). A. vera (1.5%) was the best group to moderate all histopathological lesions beside other groups. So, the A. vera (1.5 %) is useful to treat streptococcosis (caused by S. iniae) and to alter gills and liver histopathological lesions in rainbow trout.