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This study evaluated the probiotic potential of B. velezensis JW through experimental and genomic analysis approaches. Strain JW showed antimicrobial activity against a broad range of fish pathogenic bacteria including Aeromonas hydrophila, Aeromonas salmonicida, Lactococcus garvieae, Streptococcus agalactiae, and Vibrio Parahemolyticus. Fish (Carassius auratus) were fed with the diets containing 0 (control), 10, and 10 cfu/g of B. velezensis JW for 4 weeks. Various immune parameters were examined at 1, 2, 3, and 4 weeks of post-feeding. Results showed that JW supplemented diets significantly increased acid phosphatase (ACP), alkaline phosphatase (AKP), and glutathione peroxidase (GSH-PX) activity. The mRNA expression of immune-related genes in the head kidney of C. auratus was measured. Among them, the interferon gamma gene (IFN- γ) and tumor necrosis factor-α (TNF-α) showed higher expression after 3 and 4 weeks of feeding (P < 0.05). The expression of interleukin-1 (IL-1) only being significantly upregulated by 10 cfu/g of JW after 1 week of feeding (P < 0.05). The upregulation of interleukin-4 (IL-4) increased over time from 1st to 4th week. The expression of interleukin-10 (IL-10) and interleukin-12 (IL-12) showed an opposite expression pattern with IL-10 significantly upregulated and IL-12 significantly downregulated by JW containing diets at 2, 3, and 4 weeks of post-feeding (P < 0.05). Moreover, fish fed with JW supplemented diets showed significantly improved survival rate after A. hydrophila infection. The analysis of the genome of JW revealed several features aiding host health and being relevant to the GIT adaptation. Four bacteriocins, three Polyketide Synthetase (PKS), and five Nonribosomal Peptide-Synthetase (NRPS) gene clusters were identified in the genome. In summary, the above results clearly proved that B. velezensis JW has the potential to be developed as a probiotic agent in aquaculture.

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The ciliate Ichthyophthirius multifiliis is one of the most pathogenic parasites of fish maintained in captivity. In this study, effects of crude extracts, fractions, and compounds from the leaves of Macleaya cordata against I. multifiliis were investigated under in vitro conditions by bioactivity-guided isolation method. The dried ethanol extract of M. cordata was extracted successively in a separating funnel with petroleum ether, ethyl acetate, chloroform and n-butanol. Among them, only the chloroform extract showed promising activity and therefore, was subjected to further separation and purification using various chromatographic techniques. Four compounds were isolated from chloroform extract, but only one compound showed potent activity. The structure of the active compound was elucidated as sanguinarine by hydrogen, carbon-13 nuclear magnetic resonance spectrum and electron ionization mass spectrometry. In vitro antiparasitic efficacy tests exhibited that sanguinarine was 100% effective against I. multifiliis at a concentration of 0.7 mg l(-1), with LC(50) and LC(90) values of 0.437 and 0.853 mg l(-1) after 4 h of exposure. In vivo antiparasitic efficacy tests showed that the number of I. multifiliis on the gills in the treatment group (in 0.9 mg l(-1) sanguinarine) was reduced by 96.8%, in comparison to untreated group at 25°C for 48 h. Mortality of fish did not occur in the treatment group during the trail, although 40% of untreated fish died. Our results indicate that the studied plant extracts, as well as sanguinarine might be potential sources of new antiparasitic drug for the control of I. multifiliis.