Can dietary Dictyota dichotoma powder affect performance, serum, and mucus immune parameters, and antioxidant defense in Zebrafish (Danio rerio)?

The present study was performed to study possible effects of Dictyota dichotoma which is a brown macroalgae on whole body extract (WBE) and skin mucus immune parameters, antioxidant enzyme activities as well as expression of growth, immune, and antioxidant related genes in zebrafish (Danio rerio). Zebrafish with an average weight of 0.3 ± 0.08 g were supplied and stocked in 12 aquariums. They were fed with different levels (0 %, 0.25 %, 0.5 %, and 1 %) of D. dichotoma powder for eight weeks. At the end of the trial, results revealed skin mucus immune parameters in fish treated with 1 % D. dichotoma were remarkably higher than control (P < 0.05). Similar results were obtained following evaluation of WBE total Ig and lysozyme activity (P < 0.05). Also, the activity of Superoxide dismutase (SOD) and glutathione S transferase (GST) were significantly increased (P < 0.05) when fish fed with 0.5 % and 1 % D. dichotoma supplemented diets. However, no significant alteration was noticed in the case of CAT (P > 0.05). The gene expression study revealed significant up-regulation of immune-related genes (LYZ and IL-1β) in fish fed D. dichotoma supplemented groups compared to the control group (P < 0.05). Regarding growth-related genes, D. dichotoma significantly increased GH and IGF1 expression in a dose-dependent manner (P < 0.05). Evaluation of SOD and CAT genes expression showed significant differences between the control group and treatments (P < 0.05). The highest increase was observed when zebrafish was fed 1 % macroalgae. In conclusion, the present findings suggested that adding 0.5–1 % of D. dichotoma powder to the zebrafish diet can positively affect fish antioxidant defense and immune system.