Confirmation of hilsa shad (Tenualosa ilisha) in Vietnamese waters: a morphological and genetic analysis

One specimen of tropical shad was caught from the Giang Thanh River, Kien Giang province, Vietnam in a survey on 16 October 2022. We identified the specimen as the hilsa shad, Tenualosa ilisha Hamilton, 1822 using morphological analysis, and further validated by its cytochrome oxidase subunit I (COI) sequence. The specimen was 418 mm long, 1428 g in weight, with a head length of 29.0% and pectoral fin length of 31.1% of its standard length. Notably, the presence of 34 scutes, a higher gill raker count and a caudal fin length within the moderate range for Tenualosa species distinguished it from T. macrura, T. toli and T. reevesii. The COI sequence of the sample matched closely to the T. ilisha. The results confirm that T. ilisha still endures Vietnamese water, where it was thought to be extinct. Climate change and Indo-Pacific Ocean currents may introduce expansion of distribution area of the T. ilisha. Further studies on distribution of the T. ilisha and other Tenualosa species and their dynamics are needed.