In this study, the dicer gene (designated as cidicer) was identified and characterized from grass carp Ctenopharyngodon idella. The complementary DNA (cDNA) of cidicer contained an open reading frame (ORF) of 5646 nucleotides (nts) encoding a putative protein of 1881 amino acids (aa). The deduced Dicer protein contained all known functional domains identified in other organisms. Tissue tropism analysis indicated that cidicer is abundantly expressed in brain, gill, head kidney, liver, spleen, heart, muscle and intestine. In the C. idella kidney (CIK) cells, messenger RNA (mRNA) expression of cidicer was significantly up-regulated at 24 h (6·36-fold, P < 0·01) after grass carp reovirus (GCRV) infection, and its transcriptional expression level was also transiently induced to a high level (6·54-fold, P < 0·01) at 2 h post-stimulation of synthetic double-stranded polyinosinic-polycytidylic potassium salt [poly(I:C)]. In vivo analysis further showed that the expression of cidicer mRNA in the liver was induced to a significantly high level at 12 h (8·46-fold, P < 0·01), and then dropped to normal level at 72 h post-challenge with GCRV. The transcriptional expression pattern of cidicer in the spleen tissue was similar to that of liver tissue upon GCRV challenge. These results collectively implied that the identified cidicer was an inducible gene responding to viral infection both in vitro and in vivo, and the data would shed light on the interaction between RNA interference (RNAi) antiviral pathway and aquareovirus infection.

Oriental river prawn, Macrobrachium nipponense, is a commercially important freshwater prawn species in China, Japan, Korea and Vietnam. Due to overfishing for food, the wild stocks M. nipponense are endangered. Twenty microsatellite loci were isolated from the M. nipponense. Twelve of these loci were polymorphic (seven to 16 alleles per locus), with expected heterozygosity ranging from 0.68 to 0.86 (n = 48). These polymorphic loci provide a valuable tool for assessing genetic diversity of wild and cultured populations.

Triangle sail mussel (Hyriopsis cumingii) is the most important mussel species commercially exploited for freshwater pearl culture in China. Its genetic diversity was studied among populations from the five largest freshwater lakes of China, Poyang Lake (PY), Dongting Lake (DT), Taihu Lake (TH), Hongze Lake (HZ), and Chaohu Lake (CH), by the polymorphism of the inter-simple sequence repeats (ISSRs). Polymerase chain reaction (PCR) detections showed that a total of 62 loci were amplified from eight primers; of those, 31.88%, 31.15%, 31.03%, 27.27% and 26.92%, respectively, were polymorphic in each of the five populations across all genotypes tested. The average heterozygosities were 0.4747, 0.3274, 0.2366, 0.2099 and 0.2018 in each of these populations from PY, TH, DT, CH and HZ, respectively. Phylogenic analyses showed that PY and TH populations clustered with CH and HZ and formed a group, while the DT population on its own formed a separated branch. The smallest distance (0.0404) was scored between PY and TH populations, indicative of their closest relationship; the biggest distance (0.2438) was found between PY and DT populations, suggesting their greatest divergence. The present study provided genetic basis for managing mussel stocks from these lakes separately to best preserve the genetic diversity of H. cumingii. On the other hand, since the population in PY displayed the highest genetic diversity, it may be used preferably in future selective breeding to improve pearl yield and quality.

The oriental river prawn (Macrobrachium nipponense) is an important freshwater prawn species in China. We reported the isolation and characterization of 24 novel polymorphic microsatellite loci isolated from genomic DNA in this species enriched by (CA) 15 and (CT) 15 probes. The variability of these microsatellites were tested on 60 individuals collected from Hongze Lake (China). The average allele number was 15.2 per locus, ranging from 9 to 25. The observed heterozygosity was from 0.1333 to 0.9667 and the expected heterozygosity was from 0.8391 to 0.9570. 9 of the 24 microsatellites did not conform to Hardy-Weinberg equilibrium, whereas all the microsatellite loci have shown a high degree of polymorphism information content (PIC [ 0.5). These microsatellites can be used to study economic traits of QTL position, population genetic diversity and the construction of the genetic mapping for Macrobrachium nipponense in the future.

ABSTRACT. Aeromonas hydrophila, a widespread bacterium in the aquatic environment, causes hemorrhagic septicemia in fish. In the last decade, the disease has caused mass mortalities and tremendous economic loss in cultured fish. The complement component C7 is a terminal component of complement that interacts in a sequence of polymerization reactions with other terminal complement components to form a membrane attack complex. The formation of the membrane attack complex creates a pore in the membranes of certain pathogen that can lead to their death. The objective of this study was to identify single nucleotide polymorphisms (SNPs) in the C7 gene and to assess their association with A. hydrophila resistance in grass carp. A resource population consisting of 186 susceptible and 191 resistant grass carp was constructed. We sequenced a total of 7826 bp of the C7 gene and identified 6 SNPs that were genotyped in the resource population. The SNP -1575 A>C was positioned in the promoter region of the gene. The SNP 425 C>T identified in the coding exon was a synonymous substitution in the fourth exon. Statistical analysis showed that SNP 425 C>T was associated with the incidence of hemorrhagic septicemia. The SNPs -1575 A>C, -688 T>C, and -266 A>C were highly linked together (r 2 > 0.85). No haplotypes generated with these 3 SNPs were associated with resistance to A. hydrophila in grass carp. These findings suggest that the 425 C>T polymorphism in C7 gene may be a significant molecular marker for resistance to A. hydrophila in grass carp.