Optimizing growth and pigment content of promising green microalgae and application of living microalgal cells as a sole practical diet for white shrimp larvae

Microalgae are promising feed sources for aquaculture species as they contain high levels of pigments, which can help develop proper coloration. This study aimed to economically produce living microalgal cells and apply them as practical diets for white shrimp larvae. Among the strains screened, a halotolerant Chlorella sp. SHP isolated from shrimp culture pond was selected, as it contains the highest chlorophyll and carotenoid contents of 11.14 ± 1.15 and 4.89 ± 0.21 mg/g-cell, respectively. To reduce production costs, cheap fertilizer containing nitrogen, phosphorus, and potassium (NPK) was utilized as a nutrient source for microalgae cultivation. The optimal ratio of NPK fertilizer for microalgae cultivation was 1:0.25:0.25. Optimization using response surface methodology revealed that the optimal nitrogen and salt concentrations were 1.75 g/l and 1%, respectively. The optimal light intensity was 3,000 lux. The maximum microalgal biomass obtained was 1.45 ± 0.01 g/l with improved chlorophyll and carotenoid contents up to 24.51 ± 0.03 and 11.29 ± 0.28 mg/g-cell, respectively. Scaling up the process in an 8-l tank photobioreactor with the optimal aeration rate of 0.1 air volume per liquid volume per min (vvm) increased the biomass production up to 1.72 ± 0.06 g/l. The use of living microalgal cells as a practical diet for shrimp larvae not only improved the color of the shrimp but also increased dissolved oxygen and reduced sediments in the shrimp culture pond. These strategies may contribute greatly to the aquaculture sector as they are cost-effective and can help promote ecosystem balance and minimize waste.