The taxonomy of Hysterothylacium genus remains incomplete and unclear in Turkish waters. In the present study, H. adumcum larvae were morphologically identified from Merlangius merlangus euxinus in the Black Sea, Turkey. The nuclear ribosomal ITS regions (ITS-1, 5.8S subunit, ITS-2) and the small subunit of the mitochondrial ribosomal RNA (rrnS) gene of H. aduncum were amplified and sequenced. The BLAST analysis indicated that present ITS sequences of H. aduncum were identical to that of the reference sequence of H. aduncum (accession no JX413596) recorded previously from the Black Sea, Turkey. The present rrnS gene of H. aduncum from the Black Sea, Turkey (MK886768) showed 97.94 to 99.56% identity with isolates of H. aduncum from the Mediterranean Sea (MF000685-MF000691) and the Chinese waters (MF140344). Moreover, pairwise comparison between the rrnS sequences of the H. aduncum from the Black Sea, Turkey (MK886768) and others H. aduncum isolates from the Mediterranean Sea (MF000685-MF000691), the Chinese waters (MF140344) showed differences ranged from 0.2 and 1.7%. With the present study, H. aduncum from the Black Sea was characterized for the first time by sequencing of the mitochondrial rrnS gene.