Effects of different levels of dietary wakame (Undaria pinnatifida) on growth, immunity and intestinal structure of juvenile Penaeus monodon

This experiment was conducted to investigate the effects of dietary wakame on growth, immunity and intestinal structure of Penaeus monodon. Seven formulated diets with seven different levels (0%, 1%, 2%, 3%, 4%, 5%, and 6%) of wakame were fed to triplicate groups of juvenile Penaeus monodon (mean initial weight 0.69 ± 0.03 g) for 56 days. After the 56-day trial, results showed that weight gain (WG) and specific growth rate (SGR) were firstly increased and then decreased with increasing dietary wakame levels; the maximum values of WG and SGR were found in 2% wakame diet treatment and showed significant differences with other diet treatments (P < 0.05). Feed conversion ratio (FCR) was firstly decreased and then increased with increasing dietary wakame levels (P < 0.05), the minimum value of FCR was 1.13 in 2% wakame diet treatment. Protein efficiency ratio (PER) and protein retention (PR) were also firstly increased and then decreased with increasing dietary wakame levels; the maximum values of PER and PR were found in 2% wakame diet treatment and showed significant differences with other diet treatments (P < 0.05). Whole body protein content of shrimp fed 3% wakame diet was significantly higher than that of shrimp fed 0% and 1% wakame diets (P < 0.05) but without significant difference with shrimp fed other diets (P > 0.05). Whole body lipid contents of shrimp fed 3% and 4% wakame diets were significantly higher than that of shrimp fed other diets (P < 0.05). Superoxide dismutase (SOD) activity of shrimp fed 0% wakame diet was significantly lower than that of shrimp fed 6% wakame diet (P < 0.05) but without significant difference with shrimp fed other diets (P > 0.05). The higher phenoloxidase (PO) activities were found in shrimp fed 2%-6% wakame diets and showed no significant difference among them. The highest values of the intestinal folds height and width were found in shrimp fed 1% and 3% wakame diets, respectively. Second-degree polynomial regression of WG and protein retention indicated that the optimum supplement of dietary wakame should be 2.17%-2.87%.