Research on the mechanism for early development of shellfish, such as body plan, shell formation, settlement and metamorphosis is currently an active research field. However, studies were still limited and not deep enough because of the lack of genomic resources such as genome or transcriptome sequences. In the present research, de novo transcriptome sequencing was performed for Crassostrea angulata, the most economically important cultured oyster species in China, at eight early developmental stages using the 454 sequencing technology. A total of 555,215 reads were produced with an average length of 309 nucleotides that were then assembled into 10,462 contigs. As determined by GO annotation and KEGG pathway mapping, functional annotation of the unigenes recovered diverse biological functions and processes. Six unique sequences related to settlement, metamorphosis and growth were subsequently analyzed by real-time PCR. Given the lack of whole genome information for oysters, transcriptome and de novo analysis of C. angulata from the eight different developing phases will provide important and useful information on early development mechanism and help genetic breeding of shellfish.

Aquaculture is one of the world's fastest‐growing and most traded food industries, but it is under the threat of climate‐related risks represented by global warming, marine heatwave (MHW) events, ocean acidification, and deoxygenation. For the sustainable development of aquaculture, selective breeding may be a viable method to obtain aquatic economic species with greater tolerance to environmental stressors. In this study, we estimated the heritability of heat tolerance trait of Pacific abalone Haliotis discus hannai, performed genome‐wide association studies (GWAS) analysis for heat tolerance to detect single nucleotide polymorphisms (SNPs) and candidate genes, and assessed the potential of genomic selection (GS) in the breeding of abalone industry. A total of 1120 individuals were phenotyped for their heat tolerance and genotyped with 64,788 quality‐controlled SNPs. The heritability of heat tolerance was moderate (0.35–0.42) and the predictive accuracy estimated using BayesB (0.55 ± 0.05) was higher than that using GBLUP (0.40 ± 0.01). A total of 11 genome‐wide significant SNPs and 2 suggestive SNPs were associated with heat tolerance of abalone, and 13 candidate genes were identified, including got2,znfx1,l(2)efl, and lrp5. Based on GWAS results, the prediction accuracy using the top 5K SNPs was higher than that using randomly selected SNPs and higher than that using all SNPs. These results suggest that GS is an efficient approach for improving the heat tolerance of abalone and pave the way for abalone selecting breeding programs in rapidly changing oceans.

To characterize the composition of the intestinal bacterial flora in cage-cultured adult small abalone, Haliotis diversicolor, we used both culture-dependent and culture-independent approaches. In addition, in order to investigate the presence of probable pathogens, the intestinal bacterial community structures of healthy and diseased adult abalones were compared using the denaturing gradient gel electrophoresis (DGGE) fingerprinting technique. Bacteria isolated from the healthy abalone intestine belonged to the genera Vibrio, Flammeovirga, Shewanella, Persicobacter and Paraferrimonas. From the 16S rRNA gene clone library analysis, the intestinal bacterial community comprised two groups: the Proteobacteria and Tenericutes. Betaproteobacteria (18.48%), Deltaproteobacteria (30.43%) and Mollicutes (35.87%) were the most dominant components in the clones and the Mollicutes were mainly Mycoplasma-affiliated clones. The DGGE band pattern demonstrated that more bands appeared in the healthy abalones (H group) than in the diseased abalones (D group). Although few potential pathogens were detected from the D group, a clustering dendrogram indicated that individuals of the H and D groups (except for D6) formed two separate clusters. An unidentified Deltaproteobacteria species and Mycoplasma sp. were the dominant components in the intestine of both the H and the D group.Hi-Tech Research and Development (863) Program of China [2006AA10A407]; Earmarked Fund for Modern Agro-industry Technology Research System [nycytx-47]; Innovative Platform for Science and Technology, Fujian Province [2008N2004