Moi: The Pacific Threadfin of Hawaiian Shores

Pronunciation: Moi, approximately “moy,” rhyming with “boy.”

Meet the Moi

A silvery fish moving through the surge along a sandy shoreline may not look especially unusual at first. Look beneath its pectoral fins, however, and the moi reveals its signature feature: six long, thread-like filaments extending from the base of each fin.

Known in English as the Pacific threadfin or six-fingered threadfin (Polydactylus sexfilis), moi is closely associated with Hawaiian shores and has a long connection to fishpond aquaculture. It offers a different view of marine life from the brightly colored fish found around coral heads.

How to Identify Moi

Hawaiʻi’s Division of Aquatic Resources describes moi as dusky above and silvery along the sides and belly, with numerous narrow, wavy horizontal lines. Its fins have black tips, and its snout extends over the mouth.

• Color: A darker back above silvery sides and belly.
• Pattern: Narrow, wavy lines running along the sides.
• Snout: An overhanging profile.
• Fin filaments: Six long threads extending from the base of each pectoral fin.

The filaments are particularly helpful for identification. Rather than looking for ordinary whiskers on the chin, notice where these structures begin: they extend from the pectoral-fin area on each side of the body.

A Fish with “Many Fingers”

The genus name Polydactylus comes from Greek for “many fingers,” according to Hawaiʻi’s Department of Land and Natural Resources. The six filaments on each side explain the English name six-fingered threadfin as well.

Those “fingers” give the fish a memorable silhouette. They are a useful reminder that a small anatomical detail can be more informative than color when learning to recognize a species.

Where Moi Live

Moi are generally found in sandy holes along rocky shorelines or beside sandy beaches in areas with wave surge. They occur in schools rather than being described as solitary shoreline residents.

This habitat matters when searching for them. Instead of focusing only on coral structure, pay attention to the meeting places between rock, sand, and moving water. A fish guide is not a reason to enter rough conditions: shoreline waves and currents deserve respect regardless of which species might be present.

What Do Moi Eat?

Moi feed primarily on crustaceans. Hawaiʻi’s state fish manual records feeding during both daylight and nighttime hours, so they are not limited to a single daily feeding window.

This makes them different from algae grazers such as Manini and Lauʻipala. Comparing their diets reveals different ways fish find food around Hawaiian shores.

A Life That Can Include Sex Change

Moi are among the Hawaiian fishes that can change sex as they grow, developing from males into females. DLNR identifies this transition as part of the species’ biology.

Not every fish follows the same reproductive pattern. Learning about moi alongside species with different life histories shows why assumptions based on familiar land animals do not always translate neatly to marine life.

Moi and Hawaiian Fishponds

The Waikīkī Aquarium describes moi as an esteemed food fish historically raised in Hawaiian fishponds for royalty. Its aquaculture exhibit connects that history with modern captive breeding and efforts to supplement wild populations.

That connection gives moi a place in the story of Hawaiian aquaculture, not just in a list of shoreline species. Its significance comes from both the living fish and the long history of people raising and caring for it.

Young Moi Along the Shore

The state fish manual records small moi, or moi-liʻi, occurring in schools along beaches and in sheltered coves during the summer months. These observations offer another reason to learn juvenile names as well as adult fish names.

Observe schools without disturbing them, and leave fish handling and collection out of an identification outing. This guide focuses on natural history rather than current fishing rules.

Meet the Fish Behind the Cards

Our Hawaiian Reef Fish Playing Cards pair watercolor illustrations with Hawaiian and English names. Explore the full deck to bring marine discovery to the table and keep getting to know the fish of Hawaiʻi, one hand at a time.

Sources

Hawaiʻi Division of Aquatic Resources: Fishing in Hawaiʻi, A Student Manual, for identification, habitat, feeding, schooling, and juvenile observations.

Waikīkī Aquarium: Ocean Aquaculture, for historical fishpond use and modern aquaculture context.

Hawaiʻi DLNR: Moi Species Background, for the fin filaments, genus name, and male-to-female transition. Historical fishing-season information in this announcement is not used as current regulatory guidance here.