Microgeographic differences in growth, mortality, and biochemical composition of cultured Pacific oysters (Crassostrea gigas) from San Quintin Bay, Mexico

Changes in shell height, tissue dry weight (TDW), mortality, and biochemica l composition of Crassostrea gigas were evaluated at two commercial sites i n San Quentin Bay (SQB), Mexico, during the first 9 mo post-settlement. She ll growth rates were 1.5x higher at the mouth (0.36 mm d(-)1) than the head of SQB (0.23 mm d(-1)). Tissue dry weight was also 7- to 8-fold]higher in oysters From the mouth (2.1-2.16 g TDW oyster(-1)) than the head of SQB (0. 23-0.33 g TDW oyster(-1)) at the end of the 9-mo experiment. Market size (9 cm) was reached after 9 mo at the mouth and at an estimated age of 13 mo a t the head of the bay. Highest mortality occurred within the first month po st-settlement (50%-60%) and reached approximately 63% to 87% throughout the whole study period. Proteins (48%-64%) and lipids (2%-9%) were the most ab undant biochemical components during early spat development. When oysters r eached a size between 48 and 55 mm (shell height) in the fall, glycogen (1% -22% replaced lipids as the main energy depot. The changeover occurred earl ier in oysters at the mouth than in oysters from the head of the bay. it is suggested that between-site differences in growth and biochemical composit ion in oysters are the result of longer immersion/feeding period experience d by oysters at the mouth of SQB.