Use of laboratory assays to predict subsequent growth and survival of Pacific oyster ( Crassostrea gigas) families planted in coastal waters

Selective breeding programs for improving Pacific oyster ( Crassostrea gigas) stocks are expensive, labor-intensive, and typically rely on lengthy field trials in which selection for survival is compromised by inherent stochasticity of outbreaks of “summer mortality syndrome.” Reliable laboratory assays that identify and eliminate poor-performing families prior to planting could improve selection efficiency. We tested the hypotheses that juvenile survival after heat shock and/or gene transcription before or after heat shock predicts adult weight and survival at harvest for full-sib families of the Pacific oyster. We heat-shocked (41 °C for 1 h) juveniles from each of 46 families, monitored their survival for 6 d and classified families with > 69% survival as high-surviving and those with < 31% survival as low-surviving. We also deployed replicated groups of unstressed siblings from all 46 families at one subtidal and one intertidal site in Yaquina Bay, Newport, OR for two years. At harvest, we estimated family-specific average survival (%) and average individual weight (g). We found no significant family-level correlations between juvenile survival after heat shock and subsequent survival or average individual weight at the subtidal site or the intertidal site ( P > 0.05). In a separate experiment, we heat-shocked (39 °C, 1 h) another 25 juveniles from four low-surviving and four high-surviving families from the same cohort, extracted mRNAs from whole bodies collected before and at 6 h and 24 h after heat shock, and measured the mRNA concentrations of 14 candidate ESTs relative to a housekeeping gene ( elongation factor 1) using real-time quantitative PCR. The mRNA concentration of galectin was greater in low-surviving families before heat shock, whereas that of cystatin B at all sampling times and of glutathione S-transferase omega at 24 h after heat shock were greater in high-surviving families. The pre-stress differences in transcription between the family types suggest that survival of stress may be related to both constitutive differences in transcription between family types as well as induced responses to heat shock. The concentrations of heat shock protein 27, catalase, prostaglandin E receptor, gpox, and superoxide dismutase mRNA in juveniles were significantly correlated with adult survival, final individual weight or both. Additionally, mRNA concentrations of galectin and a gene with no match in Genbank, BQ426658, were correlated with average we