The control region of mitochondrial DNA (mtDNA) in sturgeon contains one to seven tandem nucleotide repeats 78-83 bp in size. Some sturgeon species are homoplasmic by the D-loop size (Acipenser nudiventris, A. oxyrinchus, A. sturio), some are mildly heteroplasmic (A. fulvescens, Huso huso) and some are markedly heteroplasmic (A. brevirostrum, A. medirostris, A. mikadoi, A. naccarii, and A. transmontanus). This work presents a comparison of the D-loop sequences associated with the termination of mtDNA replication in fish and the conservative sequences determining the termination of replication (TAS) in these organisms. It is proposed that the D-loop heteroplasmy in sturgeon may be associated with variation in the number of tandem repeat sequences, which can form stable spatial structures during mtDNA replication. In most sturgeon species with pronounced heteroplasmy, the energy levels required for the folding of tandem repeats containing variable number of repeated units differ minimally.