Food consumption and growth of the larvae of the Pacific oyster (Crassostrea gigas)

approved: The food consumption and growth of Pacific oyster larvae were studied in three experiments making use of a constant flow apparatus. The apparatus maintained a continuous flow of various densities of algae through test chambers containing different numbers of larvae in a factorial design. Three additional experiments were conducted in which a flow of algae was not used. These standing water experiments were conducted to study the effects of temperature, larval size, and algal density on the food consumption rate of oyster larvae. Dichromate wet oxidations were conducted on samples of oyster larvae to establish the relationship between shell length and caloric content of the larvae. These data were used to estimate the total caloric content of test populations of larvae. The constant flow experiments showed that larval growth rates increased as the density of algae flowing into the test chambers increased up to an optimum density. Subsequent increases in algal inflow density caused the larval growth rate to decline. Larval food consumption in the three standing water experiments was measured as cells consumed per larva per hour and as an instantaneous coefficient of food consumption called grazing rate. Grazing rate is essentially a measure of the proportion of the algal population that is removed by the larvae. The standing water experiments showed that larval food con sumption increased rapidly with increases in temperature from 10°C to 24°C. Grazing rate more than doubled with each increase of 5°C. In other experiments, the grazing rate of Pacific oyster larvae was found to increase exponentially with increases in larval shell length and linearly with increases in the caloric content per larva. A'third experiment showed that larval grazing rate was inversely related to algal density (i. e. , grazing rate declined with increased algal density). The number of algal cells consumed per larva per hour, on the other hand, was found to be directly related to the algal density. The possible application of a constant flow feeding system to an oyster hatchery is discussed. Food Consumption and Growth of the Larvae of the Pacific Oyster (Crassostrea gigas) by Robert Edward Malouf