Rice husk (RH) contains abundant silica such that RH silica (RHS) may be useful for possible industrial exploitation. Here, amorphous silica nanoparticles with multiple pore structures were acquired from RH by simple thermochemical processes. RHS antimicrobial activity and effects on zebrafish innate immunity against pathogen infections were evaluated. A toxicity assay showed that zebrafish exposed to an RHS dose lower than 200 μg/mL did not exhibit damage to zebrafish embryonic development or juvenile survival. RHS showed a wide spectrum of bacteriostatic activity against a variety of pathogens including antibiotic-resistant pathogens, implying its potential application as an antimicrobial agent in diverse industries. Fish exposed to 20 or 200 μg/mL RHS exhibited significantly increased mRNA expression of immune-related genes, including IL-1β, IL-6, IL-15, TNF-α, COX-2a, TLR-4a, lysozyme, and complement C3b. RHS-treated zebrafish exhibited a higher cumulative survival compared to that in control fish after infecting with Aeromonas hydrophila and Streptococcus iniae. The present results showed that a safe RHS dose enhanced innate immunity against infections without toxic effects in healthy fish, suggesting that RHS may be developed as an immunostimulant for improving health status in aquaculture.

Several studies of marine bioactive compounds have been carried out using seagrass. Enhalus acoroides is a type of seagrass that has bioactive compounds including alkaloids, flavonoids, tannins, steroids, and saponins that have potential as an antibacteria. The aim of study is to investigate the phytochemical compound contained in the crude extract of Enhalus acoroides and its antibacterial activities of Enhalus acoroides against Staphylococcus aureus. The seagrass was collected, washed, dried, grind and exposed to extraction by vacum rotary evaporator at temperature of 40°C and was analyzed for their phytoconstituents. Further, the crude extract was tested against pathogenic bacterial at different concentrations using disc diffusion method to determine the effect of bioactive compounds in E. acoroides to bacteria. In the present study, qualitative test of phytochemical from ethanol extract of Enhalus acoroides leaves contained phytochemical compound of alkaloids, flavonoids, tannins, steroids and saponins, while the extract of roots contained all of compounds except saponins. Based on research can be concluded, that Enhalus acoroides also has antibacterial activity against Staphylococcus aureus that showed by the presence of inhibition zone. The present finding suggests that the extract of seagrass Enhalus acoroides can be used an antibacterial agent from marine.