Water hyacinth Eichhornia crassipes extract as a novel immunostimulant for mangrove crab Scylla serrata

Integrating immunostimulants into the diet is the most efficient intervention in preventing the devastating effect of disease in aquaculture. For crustaceans, immunostimulants prime the innate immune response to prepare for the attack of infectious agents. In this study, the most common enzyme and gene expression markers of immunostimulant activity among crustaceans were screened to determine the most efficient marker to evaluate immune system stimulation in Scylla serrata by the dietary administration of 2.5 g/kg Eichhornia crassipes hot-water extract. Of the four markers tested in this study, two are recommended for use as markers of immunostimulation in S. serrata by E. crassipes. These were the oxidative stress-related enzyme catalase (CAT) and gene expression of the enzyme pro-phenoloxidase (Pro-PO). The significant CAT activity and Pro-PO expression have resulted from the introduction of β-glucan to the crab’s immune system which then triggered a cascade of immune defense mechanisms. The other oxidative stress-related enzyme superoxide dismutase (SOD) and gene expression of membrane-related protein toll-like receptor (TLR) were detected. However, they did not show differences in activity or expression between the control and experimental diet. Variation in activity was attributed to the absence of an infecting agent to stimulate the TLR signaling pathway further. Water hyacinth-fed juvenile mangrove crabs had the highest percentage weight gain of 32% between all dietary treatments. This suggests that the eight-day feeding duration was sufficient to exhibit substantial growth and immunostimulation in juvenile crabs. This also indicates that the water hyacinth can be an alternative source of immunostimulants for Scylla serrata