The potential effects of dietary supplementation with β-1,3 glucan and fructooligosaccharides (β-1,3 GF) on antioxidant activities, immunological response, and growth performance of Pacific white shrimp (Litopenaeus vannamei) was investigated. Four diets (iso-energetic and iso-nitrogenous) with different levels of β-1,3 GF (0, 0.5, 1.0, and 1.5 g kg⁻¹) were fed to healthy shrimp juveniles weighing 3 ± 0.5 g for 75 days. Shrimps were randomly distributed into 12 net enclosures at a density of 30 shrimp/net, and the experiment was performed in triplicate. The results revealed that long-term supplementation with 1.5 g kg⁻¹ β-1,3 GF significantly improved shrimp weight gain, feed conversion ratio, and digestive enzyme profiles compared to the control diet group. However, there were no substantial variations in the contents of moisture, crude protein, total lipids, and ash in the muscles of shrimp fed on different diets. Surprisingly, all antioxidants (superoxide dismutase, catalase, glutathione peroxidase) and immune biomarkers (lysozyme, total hemocyte count, phenol oxidase, and respiratory burst) activities were significantly elevated with increasing levels of β-1,3 GF in the shrimp diet, and the highest values were recorded in the 1.5 g kg⁻¹ diet groups. Challenge test results revealed that F. solani could cause a high mortality rate (86.7%) in a group fed a normal basal diet within 14 days at a dose of 5 × 10⁴ conidia mL⁻¹. Surprisingly, all dietary treated groups with different doses of β-1,3 GF showed high resistance against F. solani, represented by lower cumulative mortality rates (20–43.3%) compared to the control group. Moreover, most of the infected shrimp showed a typical black to brown gill lesion similar to that observed in the natural infection, where an identical fungus was successfully re-isolated from infected gills and muscles. Overall, this study recommends an appropriate incorporation level of β-1,3 GF that could enhance growth performance and improve the antioxidant activities, non-specific immunity, and disease resistance of L. vannamei, with an optimal level of 1.5 g kg⁻¹.

In the present study, Aeromonas hydrophila was isolated from Tilapia zillii and Mugil cephalus samples collected during different seasons from various Suez Canal areas in Egypt. The prevalence of A. hydrophila, virulence genes, and antibiotic resistance profile of the isolates to the commonly used antibiotics in aquaculture were investigated to identify multiple drug resistance (MDR) and extensive drug-resistant (XDR) strains. In addition, a pathogenicity test was conducted using A. hydrophila, which was isolated and selected based on the prevalence of virulence and resistance genes, and morbidity of natural infected fish. The results revealed that A. hydrophila was isolated from 38 of the 120 collected fish samples (31.6%) and confirmed phenotypically and biochemically. Several virulence genes were detected in retrieved A. hydrophila isolates, including aerolysin aerA (57.9%), ser (28.9%), alt (26.3%), ast (13.1%), act (7.9%), hlyA (7.9%), and nuc (18.4%). Detection of antibiotic-resistant genes revealed that all isolates were positive for bla_pse1 (100%), bla_SHV (42.1%), tetA (60.5%), and sul1 (42.1%). 63.1% of recovered isolates were considered MDR, while 28.9% of recovered isolates were considered XDR. Some isolates harbor both virulence and MDR genes; the highest percentage carried 11, followed by isolates harboring 9 virulence and resistance genes. It could be concluded that the high prevalence of A. hydrophila in aquaculture species and their diverse antibiotic resistance and virulence genes suggest the high risk of Aeromonas infection and could have important implications for aquaculture and public health.

Eight weeks feeding trial was carried out to assess the growth promoting and the immune-stimulatory effects of the supplementation of Amphora coffeaeformis (A. coffeaeformis) in the Nile tilapia diets and its resistance to bacterial infections. Fish were fed on diet containing 0, 10, 20 and 30 g of A. coffeaeformis per kg . Growth performance parameters and body composition of experimental fish were evaluated. Serum protein profile (albumin, globulin, total protein and A/G ratio), serum liver function enzymes, and serum lysozyme were assessed. Therefore, fish in all the experimental groups were challenged with pathogenic Aeromonas hydrophila following the feeding experiment. The results showed that the growth-promoting influence of A. coffeaeformis was observed on Nile tilapia performance, the optimum growth and feed utilization were obtained at fish maintained on 10g A. coffeaeformis kg-1 diet. A. coffeaeformis supplementation improved the protein and lipid contents in fish bodies without significant differences among them, especially when fed 20 or 30 g per kg, while no significant differences in the moisture and ash contents were observed among different treatments. As well, the physiological parameters (serum protein profile and serum lysozyme) were improved when fish were fed on A. coffeaeformis enriched diet. Besides, lysozyme activity was giving good results in 10, 20 and 30 g per kg. Fish mortality after challenged against A. hydrophila decreased with increasing A. coffeaeformis level in fish diets. These results indicated that A. coffeaeformis supplement is promising as an alternative method to antibiotics for disease prevention in Nile tilapia culture, and the optimum level of A. coffeaeformis in the fish diet should be ranged between 10 to 20 g kg-1 diet.

The effects of Citrullus colocynthis extract (CCE) and synthesized Se nanoparticles (Nano-Se) on non-specific immune response and resistance to Aeromonas sobria in Nile tilapia (Oreochromis niloticus) were investigated. Treatments included three levels of Nano-Se (0.5, 1 and 2 mg/kg of feed), three levels of CCE (0.1%, 0.3% and 0.5%) and control group (no additives). The diets were fed for 4 weeks, and biochemical indices, serum lysozyme, respiratory burst activities and antioxidant enzymes were measured on weeks 1, 2 and 4. After 4 weeks of feeding, fish were infected with A. sobria and mortalities were recorded for 14 days. Results of this study showed that feeding tilapia with CCE and Nano-Se supplements significantly enhanced biochemical indices, serum lysozymes and respiratory burst. CCE treatments had a moderate effect on superoxide dismutase and no effect on the other antioxidant enzymes. Nano-Se treatments had significantly positive effects on antioxidant enzymes. Both CCE and Nano-Se supplements reduced mortality following A. sobria infection. The lowest mortality (13%) was observed in the group fed with 2 mg/kg Nano-Se, and the highest mortality of 90% was observed in the control group. It can be concluded that C. colocynthis extract and synthesized Nano-Se supplementation added to fish feed can act as immunostimulants and enhance the immune functionality, antioxidant status and disease resistance in cultured Nile tilapia (O. niloticus).