Biochemical and Metabolic Characterization of the Manila Clam Ruditapes philippinarum in Response to Different Frozen Concentrated Microalgal Diets

This study evaluated the effects of different frozen concentrated microalgal feeds and their mixtures on the growth, digestive enzyme activity, biochemical composition, and metabolomic profiles of adult Manila clams, Ruditapes philippinarum, aiming to optimize feeding strategies for clam aquaculture. Clams were fed four diets: single species of Chlorella pyrenoidosa, Isochrysis galbana 3011, or Chaetoceros muelleri, and a mixed combination. Results showed that clams fed with C. muelleri exhibited the highest specific growth rate (p < 0.05). Digestive enzyme activities varied significantly, with the highest lipase activity observed in the I. galbana group and the highest amylase activity in the C. muelleri group (p < 0.05). Biochemical composition analysis indicated that C. muelleri supported higher glycogen storage (p < 0.05), while I. galbana increased free fatty acid content (p < 0.05). Metabolomic profiling revealed that different microalgae influenced metabolic networks, particularly lipid, amino acid, and energy-related pathways. Under the experimental conditions, C. muelleri appeared to be a more effective single-species diet for supporting growth and nutritional status in adult clams, providing useful insights for developing practical bivalve feeding strategies.