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Three species of Ammodytes
spp. are observed around the Japanese archipelago.

1. Ammodytes japonicus
Inhabits the Seto Inland Sea, Ise Bay, Wakasa Bay, Mutsu
Bay, Sanriku Coast, and around Hokkaido
2. Ammodytes heian
Inhabits Mutsu Bay, Sanriku Coast, and around Hokkaido
3. Ammodytes hexapterus
Inhabits around Ishikari Bay and Wakkanai around Hokkaido
(does not inhabit Mutsu Bay)
Before
2015, 1 and 2 were classified as Ammodytes personatus, but DNA analysis
results showed that two species were mixed. They can only be distinguished by
DNA analysis.
The distinction between Ammodytes hexapterus and 1-2 can be roughly made
by the spawning season and the number of soft dorsal fins, but in practice,
distinguishing by its external appearance is almost impossible. DNA analysis is
ideal for this species as well.
Since 2015, A. personatus has inhabited the Pacific Coast of California
from the Bering Sea and no longer inhabits the waters around Japan (Orr et al.,
2015).
There is also a confusingly-named Japanese fish, the "Shiwa-ikanago".
However, the scientific name of this species is Hypoptychus dybowskii
and it is a member of the sub-order Gasterosteoidei.