Dietary supplements of guanosine improve the growth, non-specific immunity of sea cucumber, Apostichopus japonicus Selenka, and its resistance against Vibrio splendidus

The growth response, non-specific immune activities and disease resistance were measured in sea cucumber, Apostichopus japonicus Selenka (initial average weight 6.80 +/- 0.10g), when fed diets supplemented with graded levels of guanosine from the guanosine-5'-monophosphate disodium (GMP) at 0 (control), 0.3, 0.6 and 1.2g/kg for 8weeks. The results showed that GMP supplemented at 0.6 and 1.2g/kg significantly enhanced the growth of sea cucumber. Sea cucumber fed a diet with 0.6g/kg of GMP had significantly higher intracellular superoxide anion production, nitric oxide synthase activity, lysozyme activity and the total superoxide dismutase (T-SOD) activity than those in control group (p<.05). Increased lysozyme activity and T-SOD activity were also found in sea cucumber fed GMP at 1.2g/kg. Moreover, there was significantly lower cumulative mortality after the disease challenge in sea cucumber fed the diets with 0.6 and 1.2g/kg GMP than that in control and 0.3g/kg GMP groups (p<.05), and no significant difference was observed between 0.6 and 1.2g/kg GMP groups. These results suggested that feeding GMP at a dose of 0.6g/kg could enhance growth, non-specific immunity of sea cucumber as well as its resistance against Vibrio splendidus.