GENETICS PARAMETERS FOR PERFORMANCE TRAITS OF THE PACIFIC OYSTER Crassostrea gigas

The Pacific oyster is one of the most important global aquaculture species due to its high growth potential and tolerance of a wide range of environmental conditions; however, most farmers use seed from wild, non-domesticated stocks for production. In this study we estimated genetic parameters for performance traits of oyster from the Molluscan Broodstock Program (MBP), a family-based selective breeding program to improve yields of Pacific oysters on the West Coast, USA. Covariance components were obtained using AIREMLF90, a multiple-trait animal model. A total of 15,249 records were analyzed from five generations of selectively bred oysters collected over a period of nearly 20 years.

Heritability estimates for initial weight at planting and field traits at harvest (yield, survival and mean individual weight) were all positive over the five analyzed generations (Figure 1); however, heritabilities for survival and yield declined in the 4^th and 5^th generations, perhaps as a result of changing environmental conditions due to greater hypoxic and acidified seawater conditions occurring on the West Coast, USA. Genetic correlations among traits were mainly positive within generations, ranging from -0.31 to 0.95. Correlations between yield and survival, individual weight and initial weight were 0.41, 0.90 and 0.36 respectively. Correlations between survival and individual weight and initial weight were 0.27 and 0.16, respectively.

Low-to-medium (mean 0.16, range -0.05 to 0.40) correlations between initial weight at planting and performance traits at harvest suggest that improvement of yields based selection of initial weight at plant out will be ineffective in improving harvest yields; however, positive medium-to-high genetic correlations between harvest traits suggest that indirect gains in yield can achieved by selection for either higher growth or survival. Estimated moderate-to-high heritabilities for harvest traits indicate that these traits are under a high degree of genetic control and gains in yield would be expected as a result of selective breeding.