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Four alkaloids (Sanguinarine, 6-Methoxyl-dihydro-chelerythrine, Cryptopine and β-Allocryptopine) were isolated from aerial parts of Macleaya microcarpa (Maxim) Fedde using bioassay-guided isolation method, and the inhibitory activity of ethanolic extract, various fractions and these four alkaloids against four fish pathogenic bacteria ( Aeromonas hydrophila, Aeromonas salmonicida, Vibrio anguillarum and Vibrio harveyi) was assessed in vitro using the agar dilution method and the microdilution assay method respectively. A. hydrophila was the most sensitive strain to all the tested compounds. Minimum inhibitory concentration ( MIC) values were lower for sanguinarine against all tested Gram-negative strains than other three alkaloids, with MIC values of 12.5 mg L−1 for A. hydrophila and 50 mg L−1 to other pathogenic bacteria. Followed by 6-methoxyl-dihydro-chelerythrine, which showed considerable antibacterial activity with MIC values of 80 mg L−1 for A. hydrophila, 100 mg L−1 for V. harveyi, and 125 mg L−1 for both V. anguillarum and A. salmonicida. Cryptopine and β-allocryptopine revealed similar inhibitory activity with MIC values of 100 mg L−1 for A. hydrophila and 200 mg L−1 for other three bacterial species. These finding provided evidence that extract, as well as isolated compounds from M. microcarpa might be potential sources novel antibacterial agents for the treatment of fish infectious diseases. [ABSTRACT FROM AUTHOR]

Infectious haematopoietic necrosis virus ( IHNV) is a serious pathogenic threat to rainbow trout ( Oncorhynchus mykiss) and other salmonids. Major histocompatibility complex ( MHC) polymorphisms have been closely linked to disease susceptibility. In this study, polymerase chain reaction-single-strand conformation polymorphism, cloning and sequencing were used to examine MHC class II β chain gene ( DAB) polymorphisms and analyse their association with IHNV in rainbow trout. The DAB exon 2 was amplified from 104 resistant and 91 susceptible fish. Forty-five different alleles were identified, 30 of which were novel. Individuals possessed between one and four alleles, indicating that the genome harbours at least two closely related DAB exon 2 loci. The percentages of amino acid mutations in the peptide binding region ( PBR) and non- PBR were 66.67% and 45.28% respectively. The rate of non-synonymous substitutions occurred at a significantly higher frequency than synonymous substitutions, suggesting the existence of balancing selection for maintenance of polymorphisms at the DAB exon 2 locus. The alleles Onmy-DAB*0201 ( P < 0.001), Onmy-DAB*0904 ( P < 0.001) and Onmy-DAB*1102 ( P < 0.01) were associated with susceptibility to IHNV, while Onmy-DAB*0103, Onmy-DAB*0601 and Onmy-DAB*1402 were associated with resistance ( P < 0.001). These alleles could be used as molecular markers for IHNV resistance breeding in rainbow trout. [ABSTRACT FROM AUTHOR]

Abstract: Dactylogyrus intermedius, an oviparous monogenean parasite, is regarded as a devastating pathogen in freshwater aquaculture and ornamental fish trade, and accounts for significant economic losses worldwide. The study was undertaken to determine the differential expression of immune-related genes TNFα1, TNFα2, IL-1β2, TGFβ, iNOSa and iNOSb in goldfish gills during D. intermedius infection by real-time quantitative PCR. The results show that the expression of the pro-inflammatory cytokines (IL-1β2, TNFα1 and TNFα2) and the anti-inflammatory cytokine (TGFβ) were up-regulated at day 7 p.i. (post infection). The mRNA levels of these cytokines returned to normal levels or were down-regulated at day 21 p.i. In the cases of iNOSa and iNOSb, a significant up-regulation in iNOSa transcription levels were seen at day 14 p.i. while the expression of iNOSb gene showed a distinct up-regulation at day 7 p.i. Additionally, this study was conducted to investigate the expression of immune-related genes in different degrees of goldfish experimentally infected with the monogenean D. intermedius. The results indicated that D. intermedius infection might regulate the fish immunity by showing differential expression levels of immune-related gene. The study confirms goldfish gill acts as an important source of inflammatory molecules, as well as an active modulator of local inflammation after initially infected with D. intermedius. Moreover, the results obtained in this study could be useful towards understanding the susceptibility of goldfish to D. intermedius and mechanisms involved in protection of goldfish to ectoparasitic infections. [Copyright &y& Elsevier]