- Summer mortality of farmed Pacific oysters causes financial losses for shellfish growers, and selective breeding to improve survival of offspring is a promising way to reduce losses. This dissertation has two objectives to assist the development of tools for use in selective breeding programs.
Objective 1: Identify candidate genes for selection and use in predictive assays by examining the transcriptome response to heat shock in gill of heat-shocked (40°C, 1 h) oysters and comparing gene transcription between families with high (>65%) or low (<30%) survival after heat shock (43°C, 1 h) by using a cDNA microarray and real-time quantitative polymerase chain reaction (RT-QPCR). The mRNA concentrations of heat shock protein 27, peroxinectin, galectin, S-crystallin, collagen, and of two ESTs with no match in Genbank, BQ426658 and BQ426884, were greater overall or at individual time points in low-surviving families than in high-surviving families. The mRNA concentration of cystatin-B was greater in high-surviving families at 24 h after heat shock than in low-surviving families. These genes can be considered as candidate genes for use in selection programs and predictive assays.
Objective 2: Test for correlations between survival of heat shock as spat and field performance of adults at harvest at two growout sites, compare candidate gene transcription in whole bodies of four low-surviving and four high-surviving families, and test for correlations between candidate gene transcription in spat and field performance of adults at harvest. The correlations between survival of juveniles exposed to heat shock (41°C, 1 h) and survival, yield, or average body weight of adults at harvest were not significant. The mRNA concentration of galectin was significantly greater in low-surviving families before heat shock, and the mRNA concentrations of cystatin B at each sampling time and of glutathione s-omega at 24 h after heat shock were greater in high-surviving families. The correlations between mRNA concentrations of heat shock protein 27, catalase, superoxide dismutase, and prostaglandin E receptor 4 in juveniles and survival of adults at harvest were significant. The correlations between mRNA concentrations of galectin, BQ426658, heat shock protein 27, glutathione peroxidase, and prostaglandin E receptor 4 and weight of adults at harvest were significant. The correlations between mRNA concentrations of galectin, BQ426658, BQ426884, heat shock protein 68, glutathione peroxidase, and prostaglandin E receptor 4 with yield of adults at harvest were significant. These results demonstrate that field performance can be predicted using gene transcription assays.