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.

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.