Here, we investigated marine thraustochytrid Schizochytrium limacinum SR21 for its ability to convert waste oil, mixture of commercial oils (mCOs) and volatile fatty acids i.e., acetic acid and butyric acid into ?-3 fatty acid docosahexaenoic acid (DHA). Metabolic insights through whole cell transcriptomic aid in tracing the route of substrate assimilation. Overall design: SR21 was cultivated in Glucose, waste cooking oil (WCO), mixture of commercial oils (mCOs), acetic acid and butyric acid with concentration 20 g/L each. Total RNA was extracted from cells harvested after entire carbon was consumed i.e., 72 hr for glucose, WCO and mCOs and 96 hr for acetate and butyrate.