NUTRITIONAL-VALUE OF A SPRAY-DRIED FRESH-WATER ALGA, SPONGIOCOCCUM-EXCENTRICUM, FOR PACIFIC OYSTER (CRASSOSTREA-GIGAS) SPAT

The nutritional value of a spray-dried freshwater alga (Spongiococcum excentricum) for Pacific oyster (Crassostrea gigas) spat was assessed in two growth experiments. In Experiment 1, spat were fed for 28 days on mixtures of a live diatom, Chaetoceros muelleri, and rehydrated S. excentricum. Growth rates were positively correlated with the amount o f live algae in the diet. However, neither the dry weight nor the ash free dry weight (AFDW) of spat fed a 100% C. muelleri (100%C) diet wer e significantly higher than those of spat fed an 80% C. muelleri: 20% S. excentricum (80%C:20%S) diet. The protein, lipid and carbohydrate c ontent of spat also increased with a higher percentage of live C. muel leri in the diet, but again there were no significant differences betw een spat fed 100%C and spat fed an 80%C:20%S diet. The nutritional con tribution of S. excentricum was furthermore indicated by the significa ntly higher AFDW of spat fed 80%C:20%S compared to spat fed an 80% rat ion of C. muelleri alone. S. excentricum could therefore potentially s ubstitute a live algal diet at a 20% replacement level. In Experiment 2, S. excentricum was supplemented with either 5 or 20 mg kaolin l(-1) . The growth of C. gigas spat did not improve significantly at either level of supplementation with kaolin compared with spat fed S. excentr icum alone.