The Role of Salinity Gradient in Regulating Biomass Yield and Lipid Biosynthesis of Chlorella vulgaris for Biofunctional Feed

Salinity is a pivotal abiotic factor influencing microalgal physiology, with direct implications for biomass productivity and biochemical composition. This study investigated the effects of four salinity gradients (25, 28, 31, and 34 ppt) on the growth performance, biomass yield, chlorophyll content, and lipid accumulation of Chlorella vulgaris under controlled laboratory conditions. Cultures were maintained for seven days in a completely randomized design with three replicates per treatment. Results revealed significant (p < 0.05) differences among treatments, with the highest cell density (110.5 × 10⁶ cells/mL), biomass yield (10.25 g), chlorophyll-a concentration (3.38 mg/L), and lipid content (43.07%) observed at 34 ppt, closely followed by 31 ppt. Increased salinity within this optimal range appeared to induce moderate osmotic stress, enhancing photosynthetic pigment synthesis and redirecting metabolic flux toward lipid biosynthesis without severely compromising growth. Water quality parameters remained within optimal limits across treatments, ensuring that salinity was the primary driver of observed physiological differences. The parallel enhancement of biomass quantity and lipid quality under higher salinity conditions underscores the potential of salinity modulation as a cost-effective strategy for improving the nutritional and commercial value of C. vulgaris biomass. These findings provide a robust foundation for the development of optimized cultivation protocols in aquaculture and biofunctional feed production, particularly in saline or brackish water systems, contributing to sustainable microalgal biotechnology and the circular bioeconomy. Future applications of this research could further enhance large-scale production techniques, offering a sustainable alternative feed source for aquaculture while reducing dependency on costly ingredients, such as fish oil.