A study was conducted to investigate the antibacterial activities of allicin, one of the major essential oils of garlic, against some fish pathogenic bacteria as well as the toxic effect of allicin on monosex Nile tilapia (Oreochromis niloticus). Allicin 10% v/v solution in dimethyl sulfoxide (DMSO) was used in this study. The bacterial species investigated were Aeromonas hydrophila, A. caviae, A. sobria, A. veronii, and Streptococcus iniae. The minimum inhibitory concentrations (MICs) of allicin in DMSO against Aeromonas hydrophila was found to be 125 μg/mL, while ranged between 250–500 μg/mL for each of A. caviae, A. sobria, A. veronii. Interestingly, the MIC for Streptococcus iniae was 63 μg/mL. On contrary, allicin exists no bactericidal activity against any of the investigated bacteria. Allicin had high toxic effect on tilapia fingerlings while adult tilapia could tolerate it.

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.

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.

The fish industry has grown considerably worldwide, and fungal infections represent a significant aspect that increases economic losses and challenges through high mortality rates. The Egyptian aquaculture industry is particularly vulnerable to Saprolegnia parasitica, a deadly fish pathogen. Using phytobiotics as immunomodulators, antioxidants, and health promoters in aquaculture have been proven recently as an alternative strategy for banned malachite green. This research aimed to examine the thyme effect (Thymus vulgaris) on the immune status of cultured Nile tilapia against Saprolegniasis. A total of 50 fish (Oreochromis niloticus) with skin lesions were gathered from a private fish farm in Alexandria, Egypt. Skin swabs, gill swabs, and muscle tissue were obtained from each fish. After the mycological examination, results revealed that 35 isolates out of 150 examined samples (23.33%) were positive for fungal growth, of which 15 (10%) isolates were identified as Saprolegnia species. In addition, other fungi were detected; 5 (3.33%), 8 (5.33%), 4 (2.67%), and 3 (2%) isolates were identified as Penicillium species, Aspergillus flavus, Alternaria species, and Fusarium species, respectively. To evaluate the immunomodulatory effect of thyme, 300 healthy Nile tilapia fish with a mean weight of 30 ± 5 gm were brought to be experimentally designed; they were distributed into four groups (with three replicates) and were fed on an experimental diet including 0.0, 0.5, 1.0, and 1.5 thyme oil (gm/100gm diet) continuously for two months. Then fish were infected with S. parasitica zoospores, which were thoroughly mixed with their diet. According to results, after two months of feeding, catalase (CAT), serum lysozyme activity, and total protein dramatically increased according to the levels of thyme added; the acquisition was for the group fed on a 1.5 gm/100gm diet. Additionally, the expression of interleukin-10 (IL-10) and interleukin-1β (IL-1β) in liver tissues increased similarly. Hence, it is concluded that employing thyme would improve the well-being and yield of the farmed Nile tilapia.

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.

This study was undertaken to screen for some biomarkers of toxicity in the liver of Nile tilapia fish during subacute Diazinon toxicity (0.28 mgL-1 for 25 days) by using Targeted metabolomics analyses and quantitatively measure 17 amino acids, and also to monitor antioxidant status of liver (glutathione, peroxidase, catalase, superoxide dismutase and malondialdehyde). There were significant increases in branched chain amino acids valine, leucine and isoleucine (p>0.01, p>0.05and p>0.01) respectively. There was a significant increase in phenylalanine (an aromatic amino acid) P>0.05, a significant increase in lipid peroxidation (malondialdehyde P>0.001), and significant decreases in the activity of antioxidant enzymes (SOD, CAT, GSH-px) with p values (P>0.01, P>0.01, and P> 0.001) respectively. Histopathological examination showed diffuse hepatocellular necrosis with multifocal granuloma and massive hepatocellular vacuolation with congested sinusoids. It can be concluded that subacute toxicity of DZN in Nile tilapia is involved in proliferation and growth of tumor cells and negatively affects the antioxidant status of the liver.