Genomic selection has been widely used in terrestrial animals but has had limited application in aquaculture due to relatively high genotyping costs. Genomic information has an important role in improving the prediction accuracy of breeding values, especially for traits that are difficult or expensive to measure. The purposes of this study were to (i) further evaluate the use of genomic information to improve prediction accuracies of breeding values from, (ii) compare different prediction methods (BayesA, BayesCπ and GBLUP) on prediction accuracies in our field data, and (iii) investigate the effects of different SNP marker densities on prediction accuracies of traits in the Portuguese oyster (Crassostrea angulata). The traits studied are all of economic importance and included morphometric traits (shell length, shell width, shell depth, shell weight), edibility traits (tenderness, taste, moisture content), and disease traits (Polydora sp. and Marteilioides chungmuensis). A total of 18,849 single nucleotide polymorphisms were obtained from genotyping by sequencing and used to estimate genetic parameters (heritability and genetic correlation) and the prediction accuracy of genomic selection for these traits. Multi-locus mixed model analysis indicated high estimates of heritability for edibility traits; 0.44 for moisture content, 0.59 for taste, and 0.72 for tenderness. The morphometric traits, shell length, shell width, shell depth and shell weight had estimated genomic heritabilities ranging from 0.28 to 0.55. The genomic heritabilities were relatively low for the disease related traits: Polydora sp. prevalence (0.11) and M. chungmuensis (0.10). Genomic correlations between whole weight and other morphometric traits were from moderate to high and positive (0.58–0.90). However, unfavourably positive genomic correlations were observed between whole weight and the disease traits (0.35–0.37). The genomic best linear unbiased prediction method (GBLUP) showed slightly higher accuracy for the traits studied (0.240–0.794) compared with both BayesA and BayesCπ methods but these differences were not significant. In addition, there is a large potential for using low-density SNP markers for genomic selection in this population at a number of 3000 SNPs. Therefore, there is the prospect to improve morphometric, edibility and disease related traits using genomic information in this species.

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Mortalities of bivalve larvae and spat linked with Vibrio spp. infection have been described in hatcheries since 1959, causing potential development of resistant bacteria. A reliable and sustainable solution to this problem is yet to be developed. Potential treatment of bacterial infection with bacteriophages is gaining interest in aquaculture as a more sustainable option for managing Vibrio spp. infection. This study assessed the effectiveness of bacteriophages (Φ-5, Φ-6, and Φ-7) against pathogenic Vibrio isolates (USC-26004 and USC-26005). These phage isolates were found to belong to the Myoviridae viral family. A total of 212 ORFs of Φ-5 were identified and annotated. The genome of this phage contained putative thymidine kinase and lysin enzyme. During infections with phages, the OD values of the isolates USC-26005 and USC-26004 remained stable at a much lower reading compared to the control after 9 h of incubation. Mortality rate of oyster (Saccostrea glomerata) larvae was 28.2 ± 3.5% in the bacteriophage treatment group, compared to 77.9 ± 9.1% in the bacterial treatment group after 24 h incubation. Findings of this study indicate that lytic phages might be utilized as potential bio-control agents of luminescent bacterial disease in oyster hatcheries.