A Novel Coelastrella tenuitheca Isolate Enhances Growth, Immunity, and Gene Expression in Whiteleg Shrimp

In this study, the freshwater microalga Coelastrella terrestris NIOF17/005 was utilized as a feed additive for the Pacific whiteleg shrimp (Litopenaeus vannamei). Coelastrella terrestris was characterized morphologically, phylogenetically (using 18s rRNA), and biochemically. Shrimp diets were supplemented with C. terrestris at 0, 1, 2.5, and 5 g/kg. After a 56-day feeding trial, the biochemical analysis of C. terrestris revealed a composition of 38.12% protein, 37.82% lipids, and 15.75% carbohydrates, with valuable bioactive compounds including polyunsaturated fatty acids and antioxidant substrates. The supplementation of 2.5 g/kg C. terrestris significantly improved the growth performance of L. vannamei (10.23 g final weight), survival rate (92.67%), and feed conversion ratio (1.71). The whole-body composition analysis of L. vannamei indicated enhanced protein content (59.74%) and lipid content (7.92%) in the algal-supplemented groups in comparison to the control. Digestive enzyme activities of amylase and lipase increased significantly, with peak activities observed at 2.5 g/kg supplementation (49.55 and 60.06 IU/L, respectively). Nonspecific immunity parameters, including lysozyme (4.47 µg/mL), superoxide dismutase (SOD; 10.77 IU/g), and catalase (CAT; 10.47 IU/g) activities, were substantially elevated in shrimp-fed C. terrestris-supplemented diets, with optimal levels at 2.5 g/kg. The gene expression analysis showed that both studied growth-related genes and immunity-related genes were upregulated. These genes reached their maximum expression at a supplementation level of 2.5 g/kg, with the expression levels being approximately 2–3 times higher in the supplemented group in comparison to the control group. In conclusion, these findings suggested that the inclusion of C. terrestris NIOF17/005 (2.5 g/kg) into shrimp feed formulations could enhance productivity, improve shrimp health, and potentially increase the sustainability of shrimp farming operations.