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.

This study was intended to address, the effect of oxytetracycline, erythromycin, and streptomycin on the antimicrobial resistance of Aeromonas sp. isolated during the production process, from infected common carp (Cyprinous carpio). Antimicrobial resistance patterns were defined by determination of minimal inhibitory concentrations (MIC) of three antimicrobial drugs, and bacteria. Results indicated that In vitro bactericidal activity, oxytetracycline showed lowest number of bacterial colonies (1×10-4 c.f.u./ml) than erythromycin (3×10-4) and streptomycin (4.5×10-4) compared to the control (9×10-4). Oxytetracycline showed the highest maximum zone of inhibition (20 mm) than erythromycin (18 mm) and streptomycin (15 mm) in antibiotic susceptibility test. In infection inhibition assay, serum from oxytetracycline fed diets inhibited Aeromonas infection to common carp. The susceptibility of the fish fed antibiotics (50 µg/mg feed) and challenge with Aeromonas sp. (1×10-4) was examined for 30 days. There was high relative percent of survivility (RPS) in oxytetracycline was 73%. Very low RPS 63% and 47.37% was found in erythromycin and streptomycin against Aeromonas sp. infection. These results demonstrated that the oxytetracycline might be a potential for Aeromonas sp. infection to common carp (Cyprinous carpio).