Evaluation of macroalgal detritus as food source for juvenile Manila clam, Ruditapes philippinarum : Effects on growth, amino acid content and fatty acid composition

Abstract

Sufficient high-quality microalgae are required for indoor nursery of juvenile Ruditapes philippinarum. However, culturing numerous microalgae to support clam feeding is a heavy burden on many hatcheries. The effects of detritus from the macroalgae Ulva pertusa, Chondrus ocellatus and Undaria pinnatifida on the growth, amino acid content and fatty acid profile of R. philippinarum were assessed as potential substitute diets. The green microalga Tetraselmis cordiformis served as comparative diet. Results revealed that the clams ingesting distinct diets presented no significant differences in growth of soft tissues, but the nutritional component of these clams differed dramatically. The clams fed with Undaria + Tetraselmis had the highest content of essential amino acids and proteins. In addition, the clams fed with single macroalgal diets and mixed macroalgal detritus and Tetraselmis showed significantly higher or statistically equal levels in n-3/n-6 ratio and docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio with respect to Tetraselmis diets. The relative percentages of EPA and DHA in clams fed with Undaria were 28% and 63% higher than those fed with Tetraselmis, and the arachidonic acid abundances in clams ingesting Undaria + Tetraselmis and Tetraselmis were significantly higher than those in clams ingesting other diets. Together, the diets containing single Undaria or mixed Undaria + Tetraselmis produced Manila clams with nutritional advantages in terms of essential amino acids and polyunsaturated fatty acids. Thus, the detritus of macroalgae, especially Undaria, is an appropriate substitute diet, at least partially, for culture of nutrition-improved R. philippinarum.