Taxonomic notes: Synonym = Hippocampus japonicus Kaup, 1856.

Confirmed distribution: Japan, Suspected distribution: Cambodia, China, Thailand, Viet Nam (Lourie et al. 2004).

Follow the link below for map of the known range of H. mohnikei.

No research has focused on the in situ ecology of adult H. mohnikei. One study has examined planktonic juveniles of the species that range in size from 6.0–65.3 mm (standard length (SL) as measured from the tip of the tail to the dorsal margin of the opercular opening and from this point to the tip of the snout) (Kanou and Kohno 2001). These juveniles were found in plankton tows from May–January. Young from 15–34 mm SL showed high gut fullness and had consumed small prey including Oithona davisae and Penilia avirostris. In contrast, large planktonic individuals ≥35 mm showed low gut fullness, preying on larger but less abundant prey items such as species of Brachyura.

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The entire genus Hipppocampus is listed on Appendix II of the CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora), effective May 2004. H. mohnikei is listed (as H. japonicus) as Vulnerable in the 1994 Viet Nam Red Data Book (Lourie et al. 2004).

• 5.4.1 International level
• 2.1 Site/area management
• 5.1.1 International level
• 4.3 Awareness & communications
• 4.2 Training

For this species, a large portion of its putative range has not been confirmed. There is no information on densities from these areas or natural/anthropogenic activities that may impact natural populations. Therefore, it is not possible to assess trends in species numbers. However, its known habitats, a) Zostera seagrass beds in inlet water (Masuda et al. 1984), and b) estuaries (Viet Nam) (Lourie et al. 1999), are both coastal zones subject to intense fishing, boating and habitation pressure in areas of Asia such as Cambodia, China, Thailand and Viet Nam where the species is thought to occur. Common sense suggests that threats are likely to exist and that populations may be under pressure. There is no evidence for a dried trade in this species at present.

• Kanou, K. and Kohno, H. 2001. Early life history of a seahorse, Hippocampus mohnikei, in Tokyo Bay, Japan. Icthyological Research 48: 361–368.
• Kuiter, R.H. 2000a. Seahorses, Pipefishes and their Relatives. A Comprehensive Guide to Syngnathiformes. TMC Publishing, Chorleywood, UK.
• Lourie, S.A., Foster, S.J., Cooper, E.W.T. and Vincent, A.C.J. 2004. A Guide to the Identification of Seahorses. Project Seahorse and TRAFFIC North America, University of British Columbia and World Wildlife Fund, Washington D.C.
• Lourie, S.A., Pritchard, J.C., Casey, S.P., Ky, T.S., Hall, H.J. and Vincent, A.C.J. 1999. The taxonomy of Vietnam's exploited seahorses (family Syngnathidae). Biological Journal of the Linnean Society 66: 231–256.
• Masuda, H., Amaoka, K., Araga, C., Uyeno, T. and Yoshino, T. 1984. The fishes of the Japanese Archipelago. Tokai University Press, Tokyo, Japan.