This study evaluated the dietary effects of an ultrasound-assisted extract of Origanum vulgare on the growth, antioxidant and immune responses (serum and mucosal) and resistance of zebrafish (Danio rerio) against Aeromonas hydrophila. Four hundred and forty adult zebrafish were distributed into 12 tanks and fed 4 experimental diets including 0% (control), 0.5% (M1), 1% (M2) and 2% (M3) of the extract per kg⁻¹ diet for eight weeks. Fish were then challenged with A. hydrophila and mortality was recorded for 10 days. Results revealed that the extract exerted potent effects on growth parameters of weight gain and specific growth rate. The feed conversion ratio was significantly lower in fish fed extract-incorporated diets. O. vulgare extract improved antioxidant and immune responses, resulting in less sensitivity to oxidative stress and a higher survival rate when challenged with A. hydrophila. Overall, the greatest effects were observed in individuals with 1% dietary inclusion of the extract. These results suggest that the extract from the plant Origanum vulgare possesses a great potential to be used in the aquaculture industry and that zebrafish is an appropriate model for nutrition studies.

This study was conducted to compare the effects of commercially available (C) and green synthesized (GS) Zinc oxide nanoparticles (ZnO-NPs) on immunological responses of common carp (Cyprinus carpio) skin mucus. GS ZnO-NPs were generated using Thymus pubescent and characterized by UV–vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX). Fish (n = 150) were randomly allocated into five groups in triplicate and received a waterborne concentration of 0% (control), 25%, and 50% of LC50 96 h of commercially available (C1 and C2) and green synthesized ZnO-NPs (GS1 and GS2) for 21 days. Results from XRD displayed ZnO-NPs with 58 nm in size and UV-vis DRS, EDX, and FT-IR analysis showed that some functional groups from plant extract bonded to the surface of NPs. The SEM images showed that ZnO-NPs have conical morphology. Acute toxicity study showed a higher dose of LC50_96h for green synthesized ZnO-NPs (78.9 mg.L⁻¹) compared to the commercial source (59.95 mg.L⁻¹). The highest activity of lysozyme and alternative complement activity (ACH50) were found in control and GS1 groups. A significant decrease in alkaline phosphatase activity (ALP) was found in C1 and C2 groups compared to other treatments. Protease activity (P) was significantly decreased in the C2 group compared to the control and GS groups. Total immunoglobulin (total Ig) content was the highest in the control. In addition, total Ig in the GS1 group was higher than GS2. The exposure to ZnO-NPs lowered total protein content in all experimental groups when compared to control. Present findings revealed lower induced immunosuppressive effects by green synthesized ZnO-NPs on key parameters of fish skin mucus.