Effects of Plantago major leaf extract on growth, serum and mucosal immunity responses, and skin-related gene expression in triploid juvenile rainbow trout (Oncorhynchus mykiss)

This research explores the impacts of Plantago major leaf extract on various parameters related to growth, blood, gene expression, serum, and mucosal immunity in juvenile rainbow trout over a period of 60 days. A total of 180 triploid Oncorhynchus mykiss, averaging 10.62 ± 1.06 g, were distributed among feeding treatments containing different concentrations of Plantago major (PM) leaf extract: 0 g kg⁻¹ (control), 1, 5, and 10 g kg⁻¹ . In comparison to the control group (CG), the administration of PM notably raised final weight (5 g kg−1) and weight gain at 1 and 5 g kg−1 (P < 0.05). However, it did not affect the survival rate or feed conversion ratio (P > 0.05). Following the administration of PM, blood and biochemical parameters remained similar to the CG, except for significantly reduced aspartate aminotransferase levels at all doses and decreased cortisol levels at 5 and 10 g kg−1 (P < 0.05). Total serum immunoglobulin levels increased across all treatment groups, while serum lysozyme levels were elevated in most groups, except the 1 g kg−1 group (P < 0.05). The PM 5 g kg−1 group revealed the highest serum peroxidase and nitric oxide activities (1 and 5 g kg−1) (P < 0.05). In mucus, the 5 g kg−1 group showed notable increases in immunoglobulin, lysozyme, and nitric oxide activities compared to controls, alongside elevated protease activities across all treatments (P < 0.05). Additionally, mucus IgM levels rose in the 5 and 10 g kg−1 PM groups (P < 0.05). Administering PM at 5 g kg−1 notably increased serum CAT and SOD activities (P < 0.05). Mucus CAT levels rose in the 5 and 10 g kg−1 groups, while SOD increased in the 5 g kg−1 group (P < 0.05). The PM 5 g kg−1 group exhibited elevated mmp9, lyz, col1α1, tn-c, fgf2, and tgfb3 compared to controls and lower doses, while PM 10 g kg−1 increased LYZ and tn-c (P < 0.05). gal-3 expression showed no changes (P > 0.05). These results suggest that PM leaf extract enhances growth performance, serum and mucosal immune responses, skin gene expression, and antioxidant capacity in O. mykiss, with the 5 g kg−1 group exhibiting the most pronounced effects.