A growth trial was conducted over 10 weeks to measure the effects of dietary Silybum marianum seeds on “growth
performance, feed utilization, blood parameters, antioxidant enzymes activities and gene expression of Nile
tilapia Oreochromis niloticus fingerlings”. Five isonitrogenous and isoenergetic experimental diets were formulated to contain five levels of S. marianum seeds on the dry weight basis at 0 (control), 2.5, 5, 7.5 and
10 g kg−1 diet. The results showed that the highest weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER) and apparent protein utilization (APU) were obtained by fish fed diet supplemented with 7.5
and 10 g kg−1 S. marianum. In addition, the total serum protein concentration as well as albumin and globulin
protein fraction contents were obviously higher in fish fed either 7.5 or 10 g S. marianum seeds kg−1 diet than
other diets. The lowest level of aspartate and alanine aminotransferase was recorded in fish fed diet supplemented with 10 g kg−1 diet S. marianum. Results also showed that, the highest total antioxidant enzyme activity
of superoxide dismutase (SOD) and catalase activity (CAT) was obtained by fish fed diet supplemented with
10 g kg−1 S. marianum. The highest transcripts accumulation of growth hormone was detected in pituitary of fish
fed diet supplemented with 10 g kg−1 diet S. marianum, but the highest expression of immunoglobulin M-2 (IGM-
2) was detected in liver of fish fed diet supplemented with 7.5 g kg−1 diet S. marianum. The highest up-regulated
expression of SOD and CAT were detected in fish fed diet supplemented with 10 g kg−1 diet S. marianum seeds.
These results suggested that the best dietary S. marianum level in the diet of Nile tilapia, O. niloticus fingerlings
was 7.5 g or 10 g kg−1 diet (92.25 and 123 mg kg−1 silymarin) as a feed additive to promote growth, enhance
the immune responses, increase antioxidant activity and gene expression.