Rice Husk Silica Enhances Innate Immune in Zebrafish ( Danio rerio ) and Improves Resistance to Aeromonas hydrophila and Streptococcus iniae Infection

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.