Growth of juvenile Ostrea edulis L. fed Chaetoceros gracilis Schütt of varied chemical composition

Abstract

The chemical composition of Chaetoceros gracilis Schütt was altered by varying the nutrient conditions of the culture. The protein content of cells cultured in the complete f/2 nutrient medium (control) and the silicate-limited medium was similar, but cells from the nitrogen-limited medium contained ≈ 60% less protein. There was little change in amino-acid composition of cells from the three culture regimes. The lipid content of silicate-limited cells was more than twice that of either the control or the nitrogen-limited cells. The predominant fatty acids in the cells from all three nutrient treatments were 14:0, 16:0, 16:1ω 7, and 20:5ω3. The content of the essential fatty acid, 22:6ω3, in the control, silicate-limited, and nitrogen-limited cells was 0.23, 0.08, and 0.10 μg · (10 6 cells) −1, respectively. The carbohydrate levels of the silicate-limited and nitrogen-limited cells were, respectively, 1.6- and 3.2-fold higher than the control. The growth responses of Ostrea edulis (L.) juveniles fed the three cultures of Chaetoceros gracilis were a function of feeding ration. At high feeding ratios the highest oyster growth rates were obtained with the control C. gracilis diet. The relatively high level of the 22:6ω3 fatty acid in this diet is suggested as a possible explanation. At the lowest feeding rations, C. gracilis grown under silicate-limited conditions yielded the highest oyster growth rate of all three diets. When the growth responses of juvenile oysters fed various mixtures of the three C. gracilis cultures were examined, the highest oyster growth rates were obtained when 25% of the control algal cells was replaced with an equal number of nitrogen-limited cells. The results indicate that higher oyster growth rates are possible with additional carbohydrate, provided that adequate protein and essential fatty acids are supplied.