The Chinese sturgeon (Acipenser sinensis), a representative ancient species of Acipenseriformes, is a basal branch that diverged early from modern teleostei fishes. It shows morphological traits of both cartilaginous and bony fish, highlighting its important role in fish evolution. This study focused on the catalytic functions and expression patterns of key LC - PUFA biosynthesis enzymes, namely fatty acyl desaturases (Fads) and elongation of very long - chain fatty acids (Elovls) proteins. Previous research showed that Chinese sturgeon Fads1 and Fads2 have more similarities with those in cartilaginous and ancient bony fish. Here, we identified three crucial LC - PUFA biosynthesis elongases (Elovl2, Elovl5a, and Elovl5b) and found they are more evolutionarily related to bony fish elongases. Using the Saccharomyces cerevisiae expression system, we discovered that Elovl5a and Elovl5b can elongate C18 and C20 substrates, with a stronger preference for C18, while Elovl2 mainly elongates C20 and C22 substrates. The spatio - temporal distribution of the three elovls genes was similar to that of fads1 and fads2. All six genes had distinct tissue - specific expression patterns, but the liver had the highest expression. Temporally, their expression increased from 0 to 103 hours post - fertilization and from 0 to 20 days post - hatching. Molecular evolution, functional, and spatio - temporal expression analyses indicated that Chinese sturgeon's key enzymes have unique features compared to those in cartilaginous and modern bony fish. This study offers vital information on the LC - PUFA biosynthesis pathway in Chinese sturgeon and new insights into the Acipenseriforme lineage.