Commonly known as the Pacific oyster, the Crassostrea gigas (C. gigas) is the most widely farmed oyster in the world. There are two reasons for this: it’s easy to grow and can tolerate different environmental conditions. However, over the last decades sustainable production of this commercially important shellfish has been threatened globally by an infectious disease caused by Ostreid herpesvirus 1 (OsHV-1). Scientists supported by the EU-funded VIVALDI project have now identified genetic differences in some Pacific oyster families that show resistance to OsHV-1. Since these families had better survival rates against the disease, selecting individuals from them to spawn the next generation of C. gigas oysters could help improve survival against an OsHV-1 outbreak.
The virus in action
OsHV-1 is a highly contagious viral disease associated with increased mortality of Pacific oysters. Although adult oysters are also susceptible (with a mortality rate of 10-30 %), the most affected are juvenile oysters, whose mortality can reach 100 %. According to an article posted on ‘The Fish Site’, “OsHV-1 virus can infect several other bivalve species – including blue mussel, European flat oyster, wedge clam and king scallop – demonstrating the robustness and adoptability of OsHV-1 in wide range of hosts, and making it highly threatening once detected in a system.” The research team used samples taken from a C. gigas oyster population after a natural outbreak of the disease caused by OsHV-1 in the sea. In order to identify the genetic markers that affect the bivalves’ survival against the virus, tissue samples of both dead and surviving oysters were obtained in equal numbers. “The selected shellfish were genotyped using a 40,000 single-nucleotide polymorphism (SNP) array (Thermo-Fisher, AXIOM),” the article states. “The data (survival phenotype and genotype) were analysed to detect SNP markers and/or quantitative trait loci (QTLs) associated with the survival against OsHV-1, which led to the detection of two significant genomic regions.” Two genetic markers were found to explain about 50 % of the genetic variation for survival against the OsHV-1 virus and can therefore help the industry to improve Pacific oyster survival through better selection. Genetic markers identified against cardiac and pancreatic diseases in farmed Atlantic salmon have now been adopted as QTL products in the salmon fishing industry. In the same way, “the QTL markers identified for survival against OsHV-1 have a strong potential for the Pacific oyster industry,” write article authors Dr M. Luqman Aslam of VIVALDI project partner Nofima (Norway) and Dr Jean-Baptiste Lamy of project coordinator Ifremer, France’s national institute for ocean science. Dr Lamy believes that “the results of this study on genetic variation, and the QTL-findings which explain large proportions of the genetic variance, will convince oyster breeding companies to implement more carefully designed breeding programmes, and test advanced – but relatively capital intensive and efficient – solutions, such as marker assisted and/or genomic selection.” VIVALDI (Preventing and mitigating farmed bivalve diseases) was carried out by a consortium of 21 partners from 10 countries. The 4-year project ended in February 2020. For more information, please see: VIVALDI project website
VIVALDI, Pacific oyster, oyster, Crassostrea gigas, herpesvirus, OsHV-1, genetic marker