Multiple dietary administrating strategies of water hyacinth (Eichhornia crassipes) on enhancing the immune responses and disease resistance of giant freshwater prawn,Macrobrachium rosenbergii

The different products of Eichhornia crassipes leaves including dried E. crassipes powder (DEP), hot-water treated E. crassipe (HTE), hot-water extract of E. crassipe (ECE) and dreg of hot-water extract of E. crassipe extract (dECE) were produced and incorporated into the diet of the prawn, Macrobrachium rosenbergii, as an immunostimulant. Results showed that prawn fed the HTE-, ECE- and dECE-containing diets for 4 months had increased total haemocyte count, different haemocyte count, phenoloxidase activity, respiratory bursts, superoxide dismutase activity, glutathione peroxidase activity especially in HTE and ECE treatments. The phagocytic activity and clearance efficiency against Lactococcus garvieae of prawn fed the HTE- and ECE-containing diets were significantly higher than those of prawn fed the control diet at 2–4 months. The relative percentage survival of prawn fed the DEP-, HTE-, ECE- and dECE-containing diets for 4 months following 144 h challenging with L. garvieae were 19.0%, 38.1%, 38.1% and 33.3%. It was concluded that E. crassipes leaves containing an active component which was easily extracted by hot water can enhance innate immunity and resistance against pathogen of M. rosenbergii by dietary long-term administration, and the administration of HTE in the diet was the best strategy due to the availability and convenience.