Stimulatory effects of seaweed Laminaria digitata polysaccharides additives on growth, immune-antioxidant potency and related genes induction in Rohu carp (Labeo rohita) during Flavobacterium columnare infection

Stimulatory effects of dietary supplementation of large brown alga, Laminaria digitata polysaccharides (LDPs) at doses of 0, 100, 200, and 300 mg/kg diets were assessed on growth, hemato-biochemical, and antioxidant-immune variables as well as related genes expression in Indian rohu carp (Labeo rohita) during Flavobacterium columnare infection. Fish growth indices were significantly (P < 0.05) influenced by dietary LDPs and bacterial infection but not their interaction. However, growth indices of rohu carp in normal unchallenged (NuC) increased pointedly at treatments of 200 or 300 mg/kg diets with no significant difference between them. In normal challenged bacterial (NbC) groups, highest fish growth was observed at the treatment of 300 mg LDPs/kg diets. Feed intake and FCR values were significantly (P < 0.05) affected by dietary LDPs, bacterial infection, and their interaction. The highest feed intake accompanied with lowest FCR value was observed in the treatment of 200 mg LDPs/kg diets. No mortality was seen in NuC groups but lowest fish survival was observed in NbC groups fed with 0.0 and 100 mg LDPs/kg diets. Highest values of white blood cell, total protein, albumin, and globulin found in NuC fish groups administrated with 200 or 300 mg/kg diets with no differences between them. Feeding NbC fish groups on 300 mg LDPs/kg diet recovered the adverse effects of bacterial infection. It is noted that levels of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and reduced glutathione (GSH) were significantly (P < 0.05) affected by dietary LDPs, bacterial infection, and their interaction. The values of antioxidant indices were significantly (P < 0.05) higher in NuC fish groups received 200 or 300 mg LDPs/kg diets with no significant (P > 0.05) differences between them. In NbC fish groups, values of antioxidant indices were significantly (P < 0.05) lower that those in NuC fish groups. Malondialdehyde (MDA) was significantly influenced by dietary LDPs alone and its lowest values were observed in both NuC and NbC fish groups fed with 200 or 300 mg/kg diets with no differences between them. Phagocytic activity, alternate complement pathway, lysozyme, respiratory burst, peroxidase, complement C3, and immunoglobulin M values improved significantly (P < 0.05) in both NuC and NbC fish groups fed with 200 or 300 mg/kg diets with no differences between them. The mRNA manifestation of hepatic SOD, CAT, and GPx genes were significantly (P < 0.05) upregulated in both NuC fish groups fed on 200 and 300 mg LDPs/kg diets but feeding NbC fish on 300 mg LDPs/kg diets enhanced their mRNA expression. The HSP70, HSP90, TNF-alpha, IL-1 beta, and IL-8 mRNA expression in the NuC fish groups showed no significant (P > 0.05) differences due to dietary supplementation of LDPs to ruho carp, but their expressions were significantly (P < 0.05) higher in NbC fish groups; particularly at the treatment of 100 mg LDPs/kg diets. The mRNA expression of IL-10, IgM, hepcidin, and Mx1 genes were significantly (P < 0.05) upregulated in NuC fish group fed with 200 or 300 mg LDPs/kg diets. The bacterial infection downregulated their expressions but the dietary LDPs recovered the adverse effects of bacterial infection especially at 200 or 300 mg LDPs/kg diets. These results shown that the use of LDPs (200 or 300 mg/kg diets) has a valuable role in enhancing the growth, antioxidant-immune status, and inflammatory responses in rohu carp during F. columnare infection.