Elovl5 elongase is a critical enzyme involved in the highly unsaturated fatty acid (HUFA) biosynthesis. There is very little information on the evolution and functional characterization of Elovl5-a and Elovl5-b genes in common carp (Cyprinus carpio var. Jian). In the present study, the genomic sequences and structures of two putative Elovl5-like elongase genes in the common carp genome were obtained. The mRNA expression patterns of Elovl5-a and Elovl5-b in tissues, hatching carp embryos, and juveniles under nutritional regulation were investigated. The results show that the two Elovl5 elongase genes have similar organization, coding 8 exons of high identity and introns of distinct size and sequence composition. They are not allelic variants of a single gene. Both Elovl5 elongase genes are highly expressed in liver, intestine (pyloric caeca) and brain. Elovl5-a and Elovl5-b mRNAs showed increased expression from newly hatched to 20 days after hatching. The regulation of Elovl5-a and Elovl5-b in response to dietary fatty acid composition was determined in liver, brain and intestine (pyloric caeca) of common carp fed with diets: (i) fish oil (FO) rich in n-3 HUFA, (ii) corn oil (CO, 18:2n-6) or (iii) linseed oil (LO, 18:3n-3). Also the differential expression of Elovl5-a and Elovl5-b genes in liver, brain and intestine in common carps fed with different oil sources was studied. Further work aimed at the determination of the mechanisms of differential expression of the Elovl5-a and Elovl5-b in different tissues and the roles of transcription factors in regulating HUFA synthesis is in progress.