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CRITTER: Meet ulua kihikihi, the threadfin jack

Many of our Hawaiian salt water fish look very different when they are babies as opposed to being adults. The threadfin jack is so unusual looking as a baby that when divers see one, they usually have no idea what they are looking at!

Adult ulua kihikihi grow to be about 4-feet long and they look very similar to our large ulua that are such a prized fish to catch in shallow water. But the threadfin jack usually lives in water deeper than 200 feet or up in the northwest Hawaiian Island chain. I have only seen two adults in over 3,000 dives I have done in Hawaii and they were off of Ke’e Beach on Kaua‘i’s North Shore.

The baby ulua kihikihi are just bizarre looking and they look much like a man-o-war jellyfish. The body of the fish may only be 4 inches long, but their dorsal and pectoral fins look like long threads and are up to a foot long. These super interesting looking fish are very hard to get a picture of because their body shines like a mirror and they swim right below the surface where they blend in with the sun’s rays. I have only seen several of these super rare jacks and this last summer a pair of them hung out at Koloa Landing in Kaua‘i for several months. I dove with them for hours trying to get a good video clip of the pair and finally got one where you can at least see the fish clearly.

We still know so little about many of our fish species because they can live in deep water and their babies live in a totally different part of the sea than the adults do. In old Hawai‘i, the adult ulua kihikihi were more than likely never seen because they live so deep, but the babies were seen from time to time and given a descriptive name. Kihikihi means to “zigzag” and the threadfin jack does just that. It changes direction so quickly that it is super hard to follow one while diving. The moorish idol is also called kihikihi because it does the same kind of zigzag pattern when it swims and the hammerhead shark is called mano kihikihi for the same reason.

The Hawaiian Island chain is so long that it has different water temperatures in the northern region, then it does off of Hawai‘i Island. Some species prefer cooler water so they live in the northwest or in deep water off of the main Hawaiian islands and other species like warmer water, so they are more plentiful in shallow waters off of the eastern part of the chain. Kaua‘i and Ni‘ihau have both the cooler water species and the warmer water species, so it is the best place to find some of the more rare specimens. As scientists, we are starting to use more underwater drones that can shoot video down to about 300 feet, so hopefully we will see what lives there that we rarely ever get to see.

You can watch ulua kihikihi in action in my underwater marine life educational series on my website at www.underwater2web and all of my new underwater, beach and surf movies on my YouTube at Underwater2web. If you subscribe to the YouTube channel, you will be the first to see what we find with our deep water drones. All of my movies are “kid friendly” and produced to be used in school educational programs.

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Terry Lilley is a marine biologist living in Hanalei Kaua‘i and co-founder of Reef Guardians Hawai‘i, a nonprofit on a mission to provide education and resources to protect the coral reef. To donate to Reef Guardians Hawaii go to www.reefguardianshawaii.org.
Source: The Garden Island

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