Combined effects of diet and stocking density on growth and biochemical composition of spat of the Cortez oyster Crassostrea corteziensis at the hatchery

The interactive effects of diet and stocking density on growth and biochemical composition of hatchery-reared Crassostrea corteziensis spat were investigated. Specimens were maintained for 21 days in upwelling chambers with continuous flow-through of seawater containing feed. The diets were: (1) A 1:1 combination of the microalgae Isochrysis galbana and Chaetoceros mulleri, (2) A 50/50 mixture of the two microalgae and cornstarch, and (3) A 50/50 mixture of the two microalgae and wheat flour. Experimental densities of specimens per upwelling cylinder were: low (5714), medium (11,428), and high (17,142). Changes in growth of spat (shell height, total wet weight, and total volume) and biochemical composition of the meat (carbohydrates, proteins, and lipids) were measured. The diet of microalgae (firstly) and microalgae with cornstarch (secondly) led to faster growth of spat under low stocking density conditions. In contrast, spat grew significantly less in shell height, wet weight, and total volume at medium and high density when fed the microalgae/wheat flour diet. Highest protein, carbohydrate, and lipid content occurred with the diet containing only microalgae, regardless of density. Glycogen content did not vary significantly between diets 1 and 2. Our results confirm that microalgae continue to be the main food source for meeting nutritional needs of C. corteziensis spat. However, it is feasible to replace microalgae by < 50% with some smaller proportion of cornstarch without significantly affecting the nutritional balance of the diet or the biochemical composition of spat.