The hot-water extract of leaves of noni, Morinda citrifolia, promotes the immunocompetence of giant freshwater prawn, Macrobrachium rosenbergii.

The hot-water Morinda citrifolia leaf extract (HMLE) was prepared for in vitro assessment on phenoloxidase (PO) activity, respiratory bursts (RBs), and phagocytic activity (PA). Furthermore, the HMLE was administrated in the diet at 0.6, 3, and 6 g (kg diet)(-1) for Macrobrachium rosenbergii, and the potential effects on the immunocompetence of prawns were evaluated. PO activity, RBs, and PA in hemocytes incubated with the HMLE at 140, 20, 20, and 140 mg l(-1) significantly increased. The immune parameters of the total hemocyte count (THC), differential hemocyte count (DHC), RBs, PO activity, superoxide dismutase (SOD) activity, PA, transglutaminase (TG) activity and hemolymph clotting time were evaluated before and after 1, 3, 5, 7, and 9 weeks of the feeding trial. During 9 weeks of the feeding trial, higher THCs, DHCs, RBs, PO, and TG as well as accelerated clotting times were observed in prawns fed HMLE-containing diets at 0.6 g kg(-1). The mRNA expressions of prophenoloxidase, TG, crustin, and lysozyme of prawns fed HMLE-containing diets at 0.6 g kg(-1) for 9 weeks of the feeding trial significantly increased. The susceptibility of prawns fed the HMLE at 0.6 g kg(-1) to Lactococcus garvieae infection significantly decreased, and the relative survival percentage was 23.1%. We therefore found that HMLE administrated through the diet at 0.6 g kg(-1) was capable of enhancing the immunity and resistance against L. garvieae in M. rosenbergii.