The purpose of this experiment was to assess the effects of the green macroalgae (Ulva intestinalis) on growth performance, immune parameters of serum and mucus, liver enzymes and the expression of genes related to growth (GH and IGF-1), and immunity (IL1-β and Lyz) in common carp (Cyprinus carpio). The test was carried out in eight weeks with the treatments supplemented with 0 (control), 0.25%, 0.5%, and 1% macroalgae and three replications for each group. At the end of the course, growth indices, serum and mucus total protein, total immunoglobulin, lysozyme, and liver enzymes including alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase were evaluated. Additionally, the expression of growth (GH and IGF-1) and Immunity (IL1-β and Lyz) genes was evaluated using real-time PCR in the brain, liver, and intestine. Based on the results, a significant difference was observed in the levels of total protein, total immunoglobulin, and mucus lysozyme in the fish that received 1% U. intestinalis compared to the control group (P<0.05). In addition, the amount of total protein, total immunoglobulin, and lysozyme in the control group and the other treatments represented a significant difference (P<0.05). Although the initial weight did not show a significant difference among the treatments (P>0.05), the final growth parameters significantly varied in different treatments, with the highest final weight observed in fish fed with 0.25% algae (P<0.05). The results of the expression of immune genes lysozyme (Lyz) and interleukin-1 (IL-1) indicated a significant difference with the control group (P<0.05), representing an increasing pattern with the rising percentage of macroalgae (P<0.05). The supplement was also found effective in promoting the expression of growth hormone (GH) and insulin-like growth factor (IGF-1) compared to the control fish (P<0.05), revealing an increasing pattern for the IGF-1 gene with the elevated level of the supplement. In general, according to the results of the present study, U.intestinalis can be recommended in carp aquaculture, most preferably at the level of 1% of daily feed, as it could significantly enhance the growth and innate immunity of fish.
