Effects of the medicinal herb Houttuynia cordata on growth performance, antioxidant capacity, immune response and immune-related gene expression in the red swamp crayfish Procambarus clarkii

Houttuynia cordata (HC) has antitumor, antileukemic, antioxidant, antiviral and other biological activities. However, despite the emergence of severe diseases, few studies have explored the effects of HC on crustaceans. We evaluated the effects of HC on growth performance, antioxidant capacity, the immune response, immune-related gene expression and disease resistance in red swamp crayfish ( Procambarus clarkii ). A total of 1800 healthy crayfish were randomly divided into six groups: the basal diet group (0%), HC10 (1.0%) group, HC15 (1.5%) group, HC20 (2.0%) group, HC25 (2.5%) group, and HC30 (3.0%) group. The feeding experiment lasted for 8 weeks. Compared with the crayfish fed the control diet, the crayfish in all the groups fed HC-supplemented diets exhibited no increase in final body weight (FBW), specific growth rate (SGR) or weight gain (WG) and exhibited a decrease in the feed conversion ratio (FCR) (P < 0.05). The total antioxidant capacity (T-AOC) and catalase (CAT), total superoxide dismutase (T-SOD), glutathione peroxidase (GPx), lysozyme (LZM), acid phosphatase (ACP) and alkaline phosphatase (AKP) activities were significantly greater and the reactive oxygen species (ROS) and malondialdehyde (MDA) contents were lower in the hemolymph and hepatopancreas of the crayfish fed a diet supplemented with 1.5% to 3.0% HC than in those of the crayfish fed the control diet. The phenoloxidase (PO) content increased in the hemolymph of the crayfish fed a diet supplemented with 1.5% to 3.0% HC compared with that in the hemolymph of the crayfish fed the control diet (P < 0.05). Furthermore, dietary supplementation with 1.5% to 3.0% HC upregulated Rab5, Rab6, pro-phenoloxidase (proPO), crustin 1, ferritin and metallothionein expression (P < 0.05). In addition, dietary supplementation with 1.5% to 3.0% HC decreased crayfish mortality from white spot syndrome virus (WSSV) infection. These findings indicate that dietary HC supplementation at an optimum dose of 2.0% to 2.5% may effectively improve the immune response and immune-related gene expression in crayfish.