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The present study determined the protection afforded by dietary administration with Azadirachta indica extract in terms of mortality and innate immune response to Aeromonas hydrophila infection in silver carp, Hypophthalmichthys molitrix after parasitic infestation in the aquarium. The silver carp was fed with 0% (control), 1.0%, 2.0% and 3.0% supplementation diets at weeks 1, 2, and 4. 2.0% dose diet within all enriched diets showed significantly increased weight gain (WG); 51.3 ± 1.0 g from weeks 1 to 4 while the specific growth rate (SGR), and feed conversion ratio (FCR) did not change significantly when compared to the control. The hematocrit, lymphocytes, and neutrophils significantly increased when fed with 2.0% supplementation diets against pathogen. The phagocytic index, bactericidal activity significantly increased in fish fed with 2.0% dose diet from weeks 1 to 4 as compared to the control, but not with 1.0% and 3.0%. The highest protection by means of lower cumulative mortality was recorded with 2.0% diet when compared to 0%, 1.0% and 3.0% diet. This study suggested that 2.0% supplementation diet significantly influence the growth, hematology, and enhances the innate immune system in silver carp, H. molitrix against A. hydrophila.

Streptococcus iniae is an important pathogen that can cause a broad range of disease in aquatic animals. To avoid the use of antibiotics and drugs, it is critical to identify protective antigens for developing highly effective vaccines against this pathogen. Vaccination is the most effective means of preventing infectious diseases; however, few vaccines are effective against Streptococcus iniae (S. iniae) in monosex Nile Tilapia. This work presents an efficacious and safe vaccine against S. iniae infections in monosex Nile tilapia (Oreochromis niloticus). The vaccine candidate S. iniae F-1 strain administered by intraperitoneal (i.p.) injection, and consisted of inactivated antigens; both the vaccinated and nonvaccinated fishes were challenged intraperitoneally with S. iniae (1 × 10 7 CFU ml −1 ) isolates and PBS (negative control). Peripheral blood samples were collected for SDS-PAGE, phagocytosis and agglutination assays. Present results indicated that immunoglobulin M (IgM) was maximally expressed in the low-amperage electric current inactivated (ECKC) vaccinated group at 3 months post-secondary vaccination (PSV). Phagocytic activity and index increased significantly in (ECKC) vaccinated group. Furthermore, fish in (ECKC) vaccinated group exhibited significantly elevated agglutination titers compared to fish in the control group, in which almost no agglutination reaction was detected. In the efficacy test, the vaccinated fishes had a significant increase in RPS (69 and 89, respectively); the percentage mortality declined from 83 ± 0.6 and 74 ± 0.7 in challenged and control fishes to 25% ± 0.8% and 8% ± 0.8% in vaccinated and challenged fish groups, respectively. Furthermore, the level of protection observed in the field trial closely resembled that achieved on a laboratory scale. Therefore, EC-killed showed the highest molecular weight 31 kDa in SDS-PAGE and Western blot and increased RPS (91%), suggested that the EC-killed cells of S. iniae could play an important role in immunizing mono-sex Nile tilapia. The EC-killed cells of S. iniae will may safe and long-lasting protection against streptococcosis.