Nile tilapia aquaculture is a fast-growing industrial sector in Egypt. However, the progress of this industry is hindered by many challenges as poor water quality and associated bacterial infections. Aeromonas hydrophila is an important zoonotic waterborne aquatic pathogen responsible for severe outbreaks in tilapia culture so the current study aimed to investigate the prevalence of Aeromonas hydrophila in tilapia fish and their aquaculture water, the fish and water samples were collected from three farms located in Assiut and Minia Governorates, Egypt. Aeromonas hydrophila was isolated from tilapia five organs including liver, kidney, intestine, spleen and gills with a percentage of 7.1%, 6.5%, 9.1%, 5.1%, 11.7%, receptively, and from water samples with 59.7%. The isolates were molecularly confirmed as Aeromonas hydrophila in 70.9% and 82.4% of the tested isolates using 16s RNA and gyr-β primers, respectively. Aeromonas hydrophila isolates revealed a marked resistance for the tested antibiotics; amoxicillin and novobiocin (100%), streptomycin (71.4 %), chloramphenicol (57%), doxycycline and trimethoprim/Sulphamethoxazole (50%), colistin (43%), ciprofloxacin and norfloxacin (14%). The isolates showed multiple antibiotic resistance indexes ranging from 0.3 to 1. The present study highlights the Aeromonas hydrophila resistance and virulence, tilapia aquaculture health hazard to the human population, so adequate control measures should be applied. Furthermore, there is an essential need to promote an alternative non-antibiotic control in farmed fish.

The objective of this project was to develop live (LV), live attenuated (LAV), and autoclaved killed vaccines (AKV). The development of the vaccine involves utilizing two well-characterized strains of Streptococcus iniae (S. iniae), namely S. iniae 1 and S. iniae 2. S. iniae 2 was obtained from Department of Fish diseases, Faculty of Veterinary Medicine, Beni-Suef University, Egypt while S. iniae 1 strain was gifted from microbiology department, Egyptian Drug Authority, Dokki, Giza, Egypt. Pathogenicity test and lethal dose determination were performed. To conduct the experiment, apparently healthy Nile tilapia, Oreochromis niloticus (O. niloticus) of average weight 30±0.2g were divided into five experimental groups: T1 group, which served as a negative control and received saline; T2 group, which served as a positive control and received S. iniae 2; T3 group, which received an autoclaved killed vaccine for S. iniae 2; T4 group, which received a live attenuated vaccine for S. iniae 2; and T5 group, which received a live vaccine for S. iniae 1. At the end of the vaccination period, S. iniae 2 was introduced challenge to all groups. Serum samples were collected three weeks after vaccination to measure serum bactericidal activity, lysozyme activity, nitric oxide, alkaline phosphatase, and acid phosphatase. The findings demonstrated that the pathogenicity test reach 0 and 100% mortality rate for S. iniae 1 and S. iniae 2, respectively. Live attenuated vaccine had significantly higher protective rate than live vaccinations, while autoclaved vaccine had the best protective efficacy (88.2%). These results were confirmed through measurement some immune parameters as Serum bactericidal activity, lysozyme activity, nitric oxide, alkaline phosphatase and acid phosphatase.

Water quality is an important part of any aquaculture system. Water provides aquatic animals with oxygen, allows for waste removal, and is the conduit for their food. Similar to all other organisms, fish are heavily influenced and dependent on the characteristics of their environment. Non-optimum water physicochemical parameters as dissolved oxygen, pH, salinity, ammonia, temperature etc. can cause stress to the cultured fish and thus make them more susceptible to disease outbreaks. Nile tilapia is the most cultured fish in Egypt. While its sustainable production is hindered by many obstacles. One of them is the water quality, therefore the hygienic effects of the water parameters are important to be clear in culturing.

Water quality is an important part of any aquaculture system. Water provides aquatic animals with oxygen, allows for waste removal, and is the conduit for their food. Similar to all other organisms, fish are heavily influenced and dependent on the characteristics of their environment. Non-optimum water physicochemical parameters as dissolved oxygen, pH, salinity, ammonia, temperature etc. can cause stress to the cultured fish and thus make them more susceptible to disease outbreaks. Nile tilapia is the most cultured fish in Egypt. While its sustainable production is hindered by many obstacles. One of them is the water quality, therefore the hygienic effects of the water parameters are important to be clear in culturing.